mri of rectal cancer

Role Of MRI In Assessment Of RectalNeoplasms

AnEssay

Submitted for Fulfillment of the Master Degree in

Radio Diagnosis

By

Abd El-Fattah Reda El-Sayeh

M.B. B.Ch.

Under Supervision

Prof. Dr.Medhat Mohammed RefaatProfessor and Head Of Radio-Diagnosis

Faculty Of Medicine, Benha University

Dr. Islam Mahmoud ElshazlyLecturer of Radio-Diagnosis

Faculty of Medicine, Benha University

2015

AcknowledgementFirst and foremost, i would like to express my deepest gratitude

and thanks to Prof.Dr. Medhat Mohammed Refaatprofessor &head of radiodiagnosis, Faculty of medicine, Bnha-

University, for his support, guidance and care; he is my very

special and dear professor.

Words could not express my great appreciation and respect to

Dr. Islam Mahmoud Elshazly lecturer of Radiodiagnosis,

Faculty of medicine, Bnha-University, for his assistance and

concern throughout this work, providing this thesis with his

scientificexperience and constructive supervision.

Last, but not least, I would like to express my appreciation and

thanks to my family for their understanding, patience and

encouragement.

List of tablesTable number and title Page No

Table (1) Illustration of modified duke's staging. 15

Table (2) Illustration of TNM staging. 17

Table (3) Comparison between TNM & Dukes staging systems. 18

Table (4)Illustration of T-stage of rectal cancer. 44

Table (5)Illustration of N-stage of rectal cancer. 65

List of Contents

Title page

Introduction and Aim of the Work 1

Anatomy of the Rectum 3

MRI Anatomy 10

Pathology of Rectal Cancer 14

Clinical review of rectal cancer……………………………..19

Imaging Modalities of Rectal Carcinoma …………………23

Techniques of MR Imaging 26

MR Imaging Manifestations of Rectal Cancer 41

Summary and Conclusion 84

References 86

Arabic Summary

List of abbreviationsCRC Colorectal Cancer

CRM Circumferential Resection Margin

CT Computed Tomography

FDG 18F-FluoroDeoxyGlucose

FOV Field Of View

HRT Hormone Replacement Therapy

IMV Inferior Mesenteric Vein

MRI Magnetic Resonant Imaging

MRF Mesorectal Fascia

PET/CT Positron Emission Tomography

TME Total Mesorectal Excision

TNM Tumor, lymph Nodes, distant Metastasis

TRUS Transrectal Ultrasound

US Ultrasound

List of figures

LIST OF FIGURES

1- Coronal illustration of rectum & anal canal anatomy. 3

2- Coronal illustration of arterial supply, venous & lymphatic drainage 6of the rectum and anal canal.

3- Axial T2-weighted sequence shows normal rectal wall anatomy 10

4- Axial T2 weighted image shows Rectum is surrounded by 11mesorectal fat within the mesorectal fascia.

5- Coronal turbo spin-echo T2-weighted MR image shows the normal 12anatomy of the rectum

6- Normal anatomy of the mesorectum 13

7- Diagrammatic illustration of T stage 16

8- Coronal illustration of the rectum with a tumor extending through 22the rectal wall into the mesorectal fat and with some lymph nodes.

9- Transverse plane of endorectal US exam of rectal 23carcinomashowing a mass lesion and LN deposit

10- Oblique coronal CT reformatted image perpendicular to the tumor 24axis shows mesorectal fasciaspeculations extending into the peri-rectal fat

11- Axial and sagittal fused PET/CT images of the pelvis showed 25increased FDG uptake of recurrent rectal carcinoma after resection& chemoradiotherapy

12- Axial T1-weighted image of pelvis at level of sacro-coccygeal 28junction in patients with (a) and without (b) administered rectal gas.Measurements from rectal wall to mesorectal fascia aredemonstrated

List of figures13- Rectal adenocarcinoma. Sagittal turbo spin-echo T2-weighted MR 29

image obtained with a high-resolution phased-array surface coil showsa stenosing lesion (arrow) of the rectal lumen (*). This lesion is outsidethe potential field of view of endorectal US and endorectal coil MRimaging

14- (a,b) (a) Endorectal coil. (b) T2 weighted image using the 31endorectal coil. The bowel wall layers are shown but there is

insufficient detail from the surrounding mesorectum to adequatelystage rectal tumors

15- The sagittal T2 weighted scans are used to plan thin-section axial 32oblique scans. It is important to ensure the scans are obtained in a

plane orthogonal to the tumour to prevent over-estimation of tumourspread

16- For tumours arising below the origin of the levator muscle, scans are 33obtained in a coronal or paracoronal plane as shown

17- Scan planes used for assessing mesorectal lymph nodes. The 33mesorectum can be assessed for lymph nodes by planning a block ofcoronal slices that run parallel to the sacrum

18- Overview of the applied sequences on a whole-body magnetic 36resonance protocol for a 32-receiver channel scanner (MagnetomAvanto; Siemens Medical Solutions, Erlangen, Germany). Totalscan time is 55minutes

19- Poor coil positioning. The images shown (top left and right) have 37been obtained with the lower edge of the pelvic coil placed at thelevel of the symphysis pubis. Consequently there is poor signal tonoise ratio from the lower rectum and anal sphincter region.Repositioning the coil restores adequate signal to noise ratio

20- It is important to centre the coil correctly to the whole rectum. Thus 37the lower edge of the coil needs to be placed so that it lies at least10cm below the symphysis pubis in order to ensure adequate signalis obtained from the lower rectum and anorectal junction. The

List of figuresuppermost limit for coil placement is the sacral promontory

21- 38

A T1 weighted image has been obtained with a high spatialresolution but the bowel wall layers cannot be distinguished

22- 39

T1 fat saturated image with contrast enhancement. The bright fatsignal intensity from perirectal fat (asterisk) has been suppressedand is of low signal intensity, there is florid enhancement of theentire bowel wall (arrow) and perirectal vessels (arrowheads) whichwould not be readily distinguishable from tumor if it were present

23- 40

Motion artifact. (a) This characteristically produces a series of bandsthat degrade the image. (b)This can often be overcome by ensuringthe patient is not in discomfort, by repositioning the patient andensuring adequate abdominal compression and repeating thesequence again after swapping phase and frequency directions

24-

Sagittal turbo spin-echo T2-weighted MR image obtained with a 41high-resolution phased-array surface coil shows a stenosing lesion(arrow) of the rectal lumen

25- Rectal carcinoma. Coronal turbo spin-echo T2-weighted MR image 41shows a stage T1 tumor (*) of the rectum

26- High-resolution T2-weighted image demonstrating a T1 polypoid 43carcinoma (arrow). There is partial preservation of the submucosallayer (short arrow) seen as a thin rim of high signal intensity deepinto the tumor. The tumor does not extend into the muscularispropria layer

27- Axial T2-weighted FSE MR image demonstrating a semiannular 44plaque of tumor with central ulceration (arrowhead) and raised

List of figuresrolled edges (arrows)

28- Stage T1 rectal carcinoma. Coronal turbo spin-echo T2-weighted 45MR image shows a huge pedunculated tumor (T) on the left lateralrectal wall.

29- Stage T1 rectal carcinoma. Coronal turbo spin-echo T2-weighted 46MR image shows the tumor (T) invading the rectal wall withoutinfiltrating the perirectal fat (arrow)

30- Stage T1 rectal carcinoma.Axial turbo spin-echo T2-weighted 46MR image shows a polypoid tumor (T) on the right lateral aspectof the rectal wall protruding into the rectal lumen.

31- Stage T2 rectal carcinoma. Coronal T2-weighted MR image shows 47a stenosing neoplastic lesion

32- Stage T2 rectal carcinoma. Unenhanced T2-weighted fast spin- 47echo image shows mesorectal fascia (arrowheads) as fine linearhypointense structure enveloping mesorectum.

33- Stage T3 rectal cancer .Transverse contrast material-enhanced T1- 48weighted turbo spin-echo MR image shows rectal tumor (blackarrow) with transmural stranding (arrowheads) in mesorectal fat.Mesorectal fascia (white arrows) is clearly depicted

34- T2-w image of a stage T3 rectal tumor ) (a) Axial high-resolution 49T2-w image showing a tumor with a pushing edge. . (b) Axial T2 -w FSE image showing nodular extension with ill-defined margins.The tumor is spreading into the perirectal fat at its leading edge

35- Drawing illustrates the relationship between the CRM and rectal 50

List of figurestumors of various stages

36- CRM is safe if distance of tumor to mesorectal fascia is >6mm 51

37- Transverse T2-w image of the distance of tumor to mesorectal fascia 52

38- .Stage T3 tumor with involvement of the mesorectal fascia. 53

39- Extramural vein invasion 54

40- AxialT2-w image of tumor extending into an extramural vein 54

41- Stage T4 tumor. Axial turbo spin-echoT2-weighted MR image 55shows a neoplastic rectal lesion (arrow) disrupting the mesorectalfascia.

42- (a) Paraxial T2-weighted FSE sequence and (b) sagittal T2-weighted 55FSE sequence of a T4 cancer located in the upper third of the rectuminvading the uterus (arrows)

43- Sagittal T2-w turbo spin-echo MR image in same patient clearly shows 56that tumor originates from the rectum (black arrows).

44- (a): Transverse gadolinium-enhanced T1-w image of tumor with 57enhancing spiculations

(b):Transverse gadolinium-enhanced T1-w image in a patient withenhancing spiculations(c)Coronal T2-w FSE image of rectal tumor with pattern nodularinfiltration

45- Transverse T2-w image of bulky rectal tumor causing mass effect 58

46- Coronal FSE T2-w image of a tumor of the rectal ampulla infiltrating 59the sphincteral plane

47- Staget 3 rectal mucinous adenocarcinoma. Transverse T2-weighted 60turbo spin-echo MR images show hyperintense rectal tumor

(arrowheads) extending to mesorectal excision plane on anterior and

List of figuresleft lateral sides (arrow

48- Axial T2-w FSE MR image demonstrating a mucinous tumor 60characterized by very high signal intensity

49- (a): Axial FSE T2-w image of a mucinous tumor(b): Axial T1-w 61image (c): Coronal T2-w image

50- (a):Sagittal FSE T2-w image of a false-positive diagnosis of 63mucinous carcinoma

(b):Coronal FSE T2-w image51- Axial T2-w image shows lymph node in the region of the middle 64

rectal artery52- Axial T2-weighted FSE sequence. Inguinal lymph node metastases 64

(arrows) in a patient with low rectal cancer

53- Rectal adenocarcinoma with metastatic lymphadenopathy. Coronal 66turbo spin-echo T2-weighted MR image demonstrates a rectaltumor (*) and two enlarged lymph nodes within the mesorectal fat(arrowhead)

54- False-negative diagnosis of a regional LN 66

55- (a): T2-w FSE transverse MR image through the upper portion of 67the rectum. A node with an irregular border(b): T2-w FSE transverseMR image through the middle portion of the rectum. A high-signal-intensity node with smooth borders

56- Identification of lymph nodes at transverse T2-weighted MR 68imaging. Axial image shows two intermediate-signal-intensitylymph nodes

57- Rectal cancer with involved lateral node outside mesorectum. 69Transverse T2-weighted turbo spin-echo MR image shows enlarged,round, hyperintense lymph node (arrowheads) in left hypogastric........................... region in, suggestive of a metastatic node.

58- T2-w FSE transverse MR image shows a node of mixed signal 69

List of figuresintensity with a low-signal intensity rim (arrow head). A focus oflow signal intensity (arrow) is demonstrated within thepredominantly intermediate-signal intensity node

59- (a)Coronal T1 image of the liver in a patient under consideration for 73metastectomy showing typical hypointense hepatic metastasis(arrow). (b)Axial T1-w image. (c)Axial T2-w image,

60- (a)T1-w transverse scan with fat suppression. The hepatic 74metastasis at segment V is hypointense (arrow).

(b)Post-contrast transverse scan at arterial phase shows ahyperintense ring-like enhancement of the lesion (arrow), which iscentrally hypovascular.

(c)Post-contrast transverse scan at portal venous phase illustrateswashout of the peripheral enhancement of the metastasis

61- (a) Axial T2WI showed slight focal thickening of rectal 75wall(b)Axial DWI of the same plane demonstrated focalhyperintense area

62- Sagittal fast spin-echo T2-w image of a T3 rectal cancer (b): 76Sagittal diffusion-weighted image (c): Fused image superimposingsagittal T2-w image and color-coded map

63- (a):Sagittal T2-w FSE MR images obtained before administration of 81chemoradiotherapy to tumor with small volume(b): Sagittal T2-wFSE MR image obtained after administration of chemoradiotherapyto tumor

64- (a):: Prechemoradiation image of rectal tumor with invasio MRF and 83left Seminal vesicle

(b): Postchemoradiation image

INTRODUCTION

IntroductionColorectal cancer is the third most common cancer worldwide. Around

30-40% of colorectal cancers are located in the rectum, accounting for

5% of malignant tumors, and ranking as the fifth most common cancer in

adults. Murray T.et al. (2005).

Rectal cancer is defined as a tumor whose distal margin measured with

the rigid rectoscope is 16 cm or less from the anocutaneous line.

The prognosis of rectal cancer is influenced by several factors, such as

local tumor extent, involved lymph nodes, and the presence of distant

metastases. Among these, the presence and extent of extramural tumor

spread influence both long-term survival and the risk of local recurrence.

With the more widespread acceptance of neoadjuvant concepts, there is

an increasing need for preoperative imaging methods to aid adequate

management because treatment strategies need to be individualized

according to the depth of tumor invasion and the status of the regional

lymph nodes, while previously patients were considered for surgery

without undergoing preoperative cross-sectional pelvic imaging. Accurate

preoperative assessment is an important first step in assigning patients to

one of the available treatment strategies.Jemal A.et al. (2005).

1

INTRODUCTION

Aim of the workThe aim is to detect the role of MRI in diagnosis and staging of

rectal neoplasms preoperative&postoperatively

2

Anatomy of the Rectum

SURGICAL ANATOMY

The rectum is the part of the gastrointestinal tract extending from the upper end of

the anal canal to the rectosigmoid junction.Iafrate F. and Laghi A. (2006).Both proximal and distal limits of the rectum are controversial: the rectosigmoid

junction is considered to be at the level of the third sacral vertebra by anatomists

but at the sacral promontory by surgeons, and likewise, the distal limit is regarded

to be the muscular anorectal ring by surgeons and the dentate line by anatomists.

Herold A. et al. (2008), Beck D.E. and Roberts P. L. (2009).

Fig (1)Coronal illustration of the rectum & anal canal anatomy.Max Lahaye.et al.(2010).Recognition of the lower limits of the rectum is important because determining the

distance between a neoplastic lesion and the levator ani muscle is vital to surgical

planning. The lower end of the rectum is characterized by the insertion of the

levator ani muscle onto the rectal muscular layer. The rectum forms an acute

anorectal angle with the anal canal as it is pulled forwards by the sling formed by3


the puborectalis muscle forming a U -shaped sling.Iafrate F. and Laghi A.(2006),Salerno G.et al. (2006).

The rectum measures approximately 12-15 cm in length. Anatomically, the rectum

can be divided in to three segments: the lower third, the middle third, and the upper

third. These segments correspond (measuring from the anal verge) to the first 7-

10cm, the next 4-5cm, and the last 4-5cm.Klessen C.et al. (2007).The lower third of the rectum can be considered on anatomical and imaging

features as the area of rectum and mesorectum below the origin of the levator ani

where the mesorectum tapers sharply.Salerno G. et al. (2006).The rectum has three lateral curves: the upper and lower are convex to the right

and the middle is convex to the left. These curves correspond intraluminally to the

folds or valves of Houston. The two left-sided folds are usually noted at 7-8 cm

and at 12-13 cm, respectively, and the one on the right is generally at 9-11 cm.

The middle valve is the most consistent in presence and location and corresponds

to the level of the anterior peritoneal reflection, they can vary in number or even be

absent.Alvin C. S.et al. (2006), Beck D.E. and Roberts P. L. (2009).The rectum is characterized by its wide, easily distensible lumen, and the absence

of taeniae, epiploic appendices, haustra, or a well-defined

mesentery.Beck D.E. and Roberts P. L. (2009).

Mesorectum & mesorectal fascia

The mesorectal fascia (fascia propria of the rectum) is a connective tissue sheath

that encloses the rectum and the perirectal tissue (mesorectum), including lymph

nodes and lymphatic vessels down to the pelvic floor and acts as a natural barrier

for tumor spread.Klessen C.et al. (2007).

4


Peritoneal coverings

The upper third of the rectum is anteriorly and laterally invested by peritoneum,

the middle third is covered by peritoneum on its anterior aspect only, while the

lower third of the rectum is entirely extraperitoneal.Beck D.E. and Roberts P. L.(2009).

Anal canal

The anatomical anal canal extends from the perineal skin to the linea dentata.

Surgically, the anal canal extends from the perineal skin to the anorectal ring; this

is the circular upper border of the puborectal muscle and lies approximately 1-1.5

cm above the linea dentata.Tonino S. and Smithuis R. (2009).Prediction of sphincter involvement is important in choosing the appropriate

treatment. The anal sphincter is comprised of three layers

1. Internal sphincter: continuance of the circular smooth muscle of the rectum. At

the level of the top of the anal sphincter, fibers from the puborectalis sling join

those of the outer muscle coat and together these form the conjoint longitudinal

coat, which forms a thin muscular layer between the internal anal sphincter and the

external anal sphincter.

2. Intersphincteric space.

3. External sphincter: voluntary striated muscle, divided in three layers that

function as one unit. These three layers are continuous cranially with the

puborectal muscle and levator ani.Tonino S. and Smithuis R. (2009),Salerno G.etal. (2006).

5


Blood supply of the rectum

• The superior rectal artery: Terminal branch from the inferior mesenteric artery.

Contributing more than 80% to the rectal blood supply.HeroldA .et al. (2008).

• The middle rectal arteries: Arises from the internal iliac arteries. They are

inconstant and bilaterally present in only 10 %.

• The inferior rectal artery: Arises from the internal pudendal arteries Herold A.etal. (2008). Skandalakis L.J.et al. (2009).

Fig (2) Coronal illustration of arterial supply, venous & lymphatic drainage of the rectum andanal canal McGraw-Hill.(1983)

Venous Drainage of the Rectum

• The superior rectal veins; which enter the inferior mesenteric veins (IMV) and

drain into the portal system.

6


• The middle rectal veins,

• Inferior rectal veins; both enter the internal iliac vein and thus drain into the

systemic circulationSkandalakis L.J.et al. (2009).

This helps explain the two distinct hematogenous metastatic patterns of rectal

cancer. In the absence of liver metastases, rectal cancer can manifest with lung

metastases when a distal tumor is drained by the systemic venous system and the

inferior vena cava to the pulmonary capillary bed. However, liver metastases are

more commonly formed by way of the IMV and portal venous system or by means

of endolymphatic spread along the course of the IMV, which is the usual pathway

for the rest of the gastrointestinal tract.Alvin C. S.et al. (2006).

Lymphatic Drainage of the Rectum

Similar to the blood supply the main lymphatic drainage of the rectum is achieved

by intramural lymphatic vessels passing initially to mesorectallymph nodes, which

shows:

Upward spread along the ascending branch of the inferior mesenteric vein to

inferior mesenteric lymph nodes.

Lateral lymphatic drainage along the middle rectal artery into the internal

iliac lymph nodes.

Low rectum and anal canal shows downward spread to the perineum and

inguinal lymph nodes.Herold A.et al. (2008).

Pelvic tumors usually metastasize first to regional lymph nodes, which are specific

groups of nodes for each tumor, and are classified as N-stage disease. If tumor

spreads to a lymph node outside the defined regional nodes, this is considered M-

7


stage disease. Para-aortic nodes and Inguinal nodes are non-regional, and spread to

these nodes constitutes M1 (stage IV) disease.McMahon J.C.et al. (2010).

Nerve Supply of the Rectum

The rectum and upper anal canal are supplied by autonomic nerves, theautonomicnerves are at risk during rectal resection, and the lower anal canaland the anusreceive a somatic input via the pudendal nerves.HeroldA.etal.(2008

8

MRI ANATOMY

MRI anatomy

Therectal wall consists of three different layers thatcan be recognized at MR

imaging. T2-weighted MR imaging sequences are the mostsuitable for depicting

the rectal wall anatomy.

MR imaging can help distinguish an inner hyperintenselayer, which represents the

mucosa andsubmucosa(no differentiation is possible betweenthese two

components); an intermediate hypointense layer, which represents the muscularis

propria;and an outer hyperintense layer, which representsthe perirectal fat tissue.

Fig(3)Axial T2-weighted sequence shows normal rectal wall anatomy. Innermost

hypointense layer: mucosa(arrow). Middle, hyperintense layer: submucosa(small

arrow). Outer hypointense layer: circular and longitudinal muscle (arrowhead). WinterL.et al. (2007)

10

MRI ANATOMY

The mesorectal fascia can also be identified as a thin, low-signal intensitystructure

that envelops the mesorectumand the surrounding perirectal fat. The

mesorectalfascia is clearly visible on the posterolateralview, although it is difficult

to differentiate thisentity from the Denonvillier fascia in the anterior wall.

Fig (4)Axial T2 weighted image shows: Rectum is surrounded by mesorectal fat within

the mesorectal fascia (red arrows). P: prostate and V: seminal vesicles. On MRI the

mesorectal fat has high signal intensity on T1- and T2-weighted images. The mesorectal

fat is bounded by the mesorectal fascia, which is seen as a fine line of low signal intensity

(red arrows).Max Lahaye.et al. (2010).

The anal canal is also visualized during MRimaging of the lower rectum. Even if

the spatialresolution is low compared with endoanal coil imaging all of the major

anatomic structures(Levator ani muscle, puborectal muscle, internaland external

11

MRI ANATOMY

anal sphincters, anal canal) can easilybe evaluated with a phased-array surface

coil.FrancoIafrate. et al. (2006)

Fig (5)Coronal turbo spin-echo T2-weighted MR image shows the normal anatomy of the

rectum. The white line indicates the lower limit of the rectum at the insertion of the levator ani

muscle (arrows) on the rectal wall. The levator ani muscle forms the ceiling of the ischiorectal

fossa. Franco Iafrate. et al. (2006)

Indeed, phased-array surface coil MR imaging allows optimal visualization of the

analsphincter complex. The anal canal is seen as a cylindric structure that extends

from the insertion of the levator ani muscle onto the rectum to theexternal anal

margin. The most important componentof the anal sphincter complex is the

puborectalmuscle. This muscle inserts into the funnel shapedlevator ani muscle,

which in turn anchors the sphincter complex to the internal portion of the

pelvis.Franco Iafrate. et al. (2006).

12

MRI ANATOMY

Fig (6)Normal anatomy of the mesorectum (A) Axial turbo spin-echo T2- weighted MR imageshows the mesorectal fascia as a thin, hypointense layer(white arrowheads) surroundinghyperintense mesorectal fat. On the anterior aspect, the mesorectal fascia appears more thickenedand is difficult to differentiate from the Denonvillier fascia (black arrowheads).

(B) Photograph of a section of the explanted rectum shows perirectal fat surrounded by themesorectal fascia.

(C) Coronal turbo spin-echo T2-weighted MR image obtained with a phased-array surface coilshows a normal anal sphincter complex. The levator ani muscle (straight arrows) appears as afunnel-shaped muscular layer that extends from the obturator ani muscle to the anal canal. Thepuborectalis muscle (arrowheads) is depicted at the insertion of the levator ani muscle onto theanal canal. The external (curved arrows) and internal (*) sphincter muscles are also seen .FrancoIafrate. et al. (2006).

13

Pathology

Macroscopic pictureNon-exophytic (ulcerated) tumors tend to be more locally advanced. Exophytic

(polypoidal) tumors: have a pronounced protuberant appearance with the tumor mass

projecting into the lumen. A number of studies have observed that such polypoidal

lesions are often of a relativelylow-grade malignancy.

Morphology was not shown to be an independent predictor of outcome aftertumor

excision.McCourt M. et al. (2009), Martling A.et al. (2003).

Microscopic picture(A)Epithelial tumors:

1- Adenocarcinoma

2-Other types:

Mucinous adenocarcinoma, signet ring adenocarcinoma, squamous cell carcinoma,adenosquamous carcinoma, undifferentiated carcinoma, unclassified carcinoma,Carcinoid tumors

(B)Nonepithelial tumors:

Leiomyosarcomas, hematopoietic and lymphoid neoplasms

Adenocarcinomas account for the vast majority (98%) of rectal cancer.

Other rectal tumors are relatively rare and include carcinoid tumors

(0.1%)lymphoma (1.3%), and gastrointestinal stromal tumors (1%).Iafrate F.et al.(2006).

14

Pathology

Colloid or mucinous adenocarcinomas are defined by the large amountsof

extracellular mucin retained within the tumor (The amount of mucinrequired to

warrant a diagnosis of mucinous carcinoma, as set by the World

Health Organization, is at least ≥ 50% of the mucin pool occupying thetumor

mass).They have been associated with a higher incidence of lymph node metastases

and poorer prognosis and that they are also poor candidatesfor local excision even if

confined to the muscularis propria. The productionof mucus under pressure allows

the cancers to separate tissue planes in thebowelwall and thus to more frequently

gain access to the peritoneal cavity. In addition, the fluid produced by these tumors

is taken up by lymphaticswhich helps propel the tumor into the regional lymph

nodes.McCourt M. et al. (2009),Kim M-J.et al. (2003).

StagingStaging is the method of summarizing the anatomical extent of a malignant tumor,

thereby communicating information regarding prognosis.Smith N. and Brown G.(2008).

Stage classifications

I. Dukes Classification

This system divided tumor classification into 3 stages, as follows

Table

(1)illustration of modified duke's staging. Aspinall and Taylor-Robinson,

(2001)

15

Pathology

Dukes A: Tumor limited to the rectal wall

Dukes B: Tumor extended through the rectal wall into extra-rectal tissues

Dukes C: Metastases to regional lymph nodes.Hassan I. (2009).

This system was modified by others to include subdivisions of stages B and C, as

follows

Stage B was divided into

B1; tumor penetration into muscularis propria

B2; tumor penetration through muscularis propria

Stage C was divided into

C1; tumor limited to the rectal wall with nodal involvement

C2; tumor penetrating through the rectal wall with nodal involvement

Stage D was added to indicate distant metastases.Hassan I. (2009).

Fig (7) Diagrammatic illustration of T stage.Cancer Research UK (2003)

16

Pathology

II. TNM classification:

Primary tumor (T)

TX: Primary tumor cannot be assessed

T0: No evidence of primary tumor

Tis: Carcinoma in situ: intraepithelial or invasion of the lamina propria.

T1: Tumor invades submucosa.

T2: Tumor invades muscularis propria.

T3: Tumor invades through the muscularis propria into the subserosa, or into the

nonperitonealized perirectal tissues

T4: Tumor directly invades other organs, structures or the visceral Peritoneum.

Table (2) illustration of TNM staging.Alamo City Cancer Council (2001).

17

Pathology

Regional lymph nodes (N)

NX: Regional nodes cannot be assessed

N0: No regional lymph node metastasis

N1: Metastasis in 1-3 regional lymph nodes

N2: Metastasis in 4 or more regional lymph nodes

Distant metastasis (M)

MX: Presence of distant metastasis cannot be assessed

M0: No distant metastasis

M1: Distant metastasis

Table (3) Comparison between TNM & Dukes staging systems.Zampino M.et al. (2009)

CLINICAL REVIEW

Incidence:

Colorectal cancer (CRC) is the third most common cancer in both sexes

combined worldwide, after prostate and breast cancer. Around 30% of all

CRCs are diagnosed in the rectal anatomic site (accounting for 5% of

malignant tumors, and ranks as the fifth most common cancer in

adults).Valentini V. et al. (2008). Rectal cancer is more prevalent in the elderly population with a greater than

10-fold increase in the incidence beyond 65 years old. A decreasing trend in

the age incidence has been observed in the last decade, with a higher

incidence among males. Valentini V.,et al. (2008).Kirke R.,et al. (2007).KooB.C.,et al. (2006).

Risk factors:

The key risk factors identified for rectal cancer are:

1. Dietary components (e.g. meat, fat, and selenium), obesity, alcohol, some

medical therapies like Non-Steroidal Anti-inflammatory drugs(NSAIDs),

Hormone Replacement Therapy(HRT), statins and oralcontraceptives,

medical conditions (inflammatory bowel diseases, diabetes).Valentini V. etal. (2008).Herold A.et al. (2008).

2. Genetic factors: Individuals with a first degree relative with colorectal

cancer have approximately a twofold risk of developing colorectal cancer.

Familial adenomatous polyposis, hereditary non-polyposisare at increased

risk of developing rectal cancer.Valentini V. et al. (2008).Herold A.et al.(2008).

19

CLINICAL REVIEW

3. Synchronous lesions: Approximately 5% of colorectal cancers demonstrate

multiple lesions at diagnosis. In 35% of patients diagnosed with a primary

colorectal carcinoma, an adenomatous polyp is present elsewhere in the

colon or rectum. Second tumors are likely to be overlooked.Valentini V. etal. (2008), HassanI. (2009).

4. Irradiation: Patients with Previous irradiation to the pelvis is known to

increase the incidence of rectal cancer.Valentini V. et al. (2008).Herold A.etal. (2008).

5. Precancerous lesions:

Most rectal cancers are thought to primarily develop from

adenomatous polyps over a period of 10-15 years, known as the

adenoma-carcinoma sequence. The incidence of polyps increases with

age and the risk of malignant transformation of a polyp markedly

increases with its diameter.

The rate of malignant transformation is about 1% for polyps less than

1 cm in diameter, but 10% for larger ones.Klessen C.et

al(2007).

Prognosis:•Despite advances in the diagnosis and treatment of rectal cancer, five-year

survival rates continue to hover around the 50% mark. For cancers limited to the

bowel wall, the survival rate climbs to 83%-90%, and drops to less than 10% if

there are distant metastases, highlighting the importance of early detection and

treatment.Jemal A. et al. (2005),Alvin C. S.et al. (2006).•The prognosis of rectal cancer is directly related to a number of factors:

1. Depth of tumor invasion (local tumor extent) (T stage).Wieder H.A.et al. (2007).2. Tumor involvement in the circumferential resection margin (CRM).

20

CLINICAL REVIEW

The presence of a positive CRM has been shown to correlate with an increasing

incidence of local recurrence, systemic failure and poor survival.Burton S. et al(2006).3. Extramural venous invasion. It has been shown to be an independent poor

prognostic factor in colorectal cancer.Burton S. et al (2006).4. The number of metastatic lymph nodes (N stage).Wieder H.A.et al. (2007).

5. Distant metastases (M stage).Kim C.K., et al. (2007).6. Higher grade and mucinous adenocarcinomas show worse prognosis,

specifically with signet ring histology.Lahaye M.J.et al. (2005).

Clinical picture:

• The most common presenting symptoms in rectal cancer are altered bowel habit,

tenesmus (a feeling of incomplete evacuation) together with mucus discharge and

fresh rectal bleeding.

Rarely complete rectal cancer may present with large bowel obstruction or profuse

rectal bleeding.Herold A. et al. (2008).

• The differential diagnosis of rectal cancer includes almost all common

proctological conditions, particularly haemorrhoids, anal fissure, solitary rectal

ulcer, benign polyps, rectal prolapse and inflammatory bowel disease. In addition it

is important to distinguish carcinoma of the anal canal. Herold A. et al. (2008).

Treatment:Traditionally rectal cancer surgery consisted of excision of the tumorwith amargin of surrounding perirectal fat

21

CLINICAL REVIEW

This however resulted in high local recurrence rates up to 40%.

In 1982 the surgeon Richard John Heald introduced the total mesorectal excision.

After many years TME was widely accepted, which caused a drop in local

recurrence rates from 40% to 11%.Max Lahaye.et al. 2010.

Total mesorectal excision

Total mesorectal excision (TME) is the best surgical treatment for rectal cancer

provided that the resection margin is free of tumor. In TME the entire mesorectal

compartment including the rectum, surrounding mesorectal fat, perirectal lymph

nodes and its envelope, i.e. the mesorectal fascia is completely removed. This

minimizesthe chance of tumor remnants in the surgical bed.

Fig (8) Coronal illustration of the rectum with a tumor extending through the rectal wall into themesorectal fat and with some lymph nodes, mesorectal fascia is not involved TME can beperformed Notice the anal verge (blue arrow).Max Lahaye.et al. (2010

22

IMAGING MODALITIES

Endorectal ultrasound

Fig (9) Transverse plane of endorectal US exam of rectal carcinoma showing a mass lesion

(measured) and LN deposit (labeled). Kasr el-ainy hospital- general surgery department (2013).

• Endorectal or transrectal ultrasonography (TRUS) has a major role in rectal

cancer with up to 95% accuracy for determining trans-mural penetration and up to

74% accuracy for determining perirectal node status. TRUS is very accurate for

staging of superficial rectal tumors but is not useful for staging advanced rectal

cancer.Zampino M.et al. (2009), Beets-Tan R.G.H. and Beets G.L. (2004).

• In the imaging work up of patients with rectal metastases, abdominalUS is highly

efficient in helping to distinguish between two groups of patients with liver

metastases: the group of patients with diffuse metastases who are no longer eligible

for curative treatment and the group with no metastases or a very limited number

of them. The patientsin the latter group require CT, MR imaging, or FDG PET for

the selectionof appropriate therapeutic approaches.Bipat S. et al. (2005).

23

IMAGING MODALITIES

Computed tomography (CT)

• The advances in CT technology such as multiplanar reformatting have raised

interest for the potential role of CT for the detection and staging of rectal cancer.

However, MRI is the most reliable technique to determine the local staging of

rectal cancer because of inherently high soft tissue contrast resolution in MRI.

While CT is still primarily used for detection of metastatic disease.Kim C.K. et al.(2007).

Fig (10) Oblique coronal CT reformatted image perpendicular to the tumor axis shows

mesorectal fascia (Arrow-heads( speculations extending into the peri-rectal fat (arrows) indicates

stage T3 disease. Sinha R.et al.(2006).

Perfusion CT can have a role in staging and restaging of patients after

chemoradiotherapy. CT colonography is a potential alternative to conventional

colonoscopy for colorectal cancer screening and can be performed after incomplete

colonoscopy to assess for synchronous lesions and metastases.Zampino M.et al(2009).

24

IMAGING MODALITIES

Positron emission tomography (PET) and PET/CT

Fig (11) axial and sagittal fused PET/CT images of the pelvis showed increased FDG uptake of

recurrent rectal carcinoma after resection & chemoradiotherapy. M.Fouad Alpha scan radiologycenter (2013).

• FDG-PET (18F-fluorodeoxyglucose positron emission tomography) and

FDG-PET/CT has mainly been used for M-staging of rectal cancer to assess

hepatic metastatic disease. Bipat S.et al. (2005).

Current Uses:

Detection of residual/recurrent disease.

Staging of rectal cancer using PET/CT colonoscopy.

Radiotherapy planning; by the detection of occult nodal or distantmetastases,

change in radiation dose or intention of treatment, anda change in tumor target

volume delineation.

Predicting response to neoadjuvant chemoradiation

25

IMAGING MODALITIES

Future uses:

Markers for response assessment to targeted therapies.Valentini V. et al.(2008).

Magnetic resonance (MR) imaging

MR imaging of the rectum may be performed with either an endorectal coil

or a phased-array surface coil. In terms of patient preparation, pulse sequences, and

plane acquisition, the imaging protocols are identical (Iafrate et al., 2006).

Patient preparation

No special patient preparation is required.

Few papers report rectal cleansing 2 hours before the MRI examination with

rectal suppositories.( Chun et al.,2006). A full bladder is unnecessary and is uncomfortable with the compression from

the body coil.( Klessen et al.,2007).

Premedication

A spasmolytic agent (e.g.butylscopolamine at a dose of 20-40 mg) to

prevent artifacts caused by peristalsis of the small intestine and to distend the

sigmoid and rectum. The agent has a short half-life and is therefore injected

intramuscularly immediately before MRI(Brown et al.,2005).

Another opinion is that small bowel movement is not a problem and

therefore antiperistaltic agents are not indicated(Klessen et al.,2007).

26

IMAGING MODALITIES

Contrast medium

IV contrast medium: Current data in the literature suggests that IV contrastmedium administration does not improve staging of rectal tumors by MRI.Overstaging as a result of desmoplastic tumor reaction still occurs, andidentification of the individual rectal wall layers, particularly the submucosal layer,can still be difficult after contrast enhancement. The gadolinium-enhanced MRsequences can therefore be omitted, thus saving acquisition time and examinationcosts and avoiding potential allergic reactions(Vliegen et al.,2005).

Enteral contrast medium: Some authors recommended administration of a

positive or negative (e.g. warm water administered with a balloon-tipped rectal

tube about 150-400 ml) enteral contrast medium, to aid visualization of the primary

tumor, with the intention of improving local T staging(Klessen et al.,2007). However, this seems not to be necessary as suggested by current data in the

literature; it is increasingly recognized that local T stage may be less informative in

terms of preoperative management than the distance between the tumor and the

mesorectal fascia. In particular, T3 tumors, although penetrating through the rectal

wall by definition, may variously be several millimeters away from the mesorectal

fascia or involve it directly, with the result that preoperative treatment is variable

despite identical T staging. Also, T2 tumors located at the anorectal junction come

very close to the resection margin despite not penetrating the bowel wall (Slater etal.,2006).

In this point of view any procedure that impairs accurate measurement of the

distance between the tumor and the mesorectal fascia should be avoided as rectal

overdistension significantly reduces the distance between the rectal wall and the

mesorectal fascia (fig.32), this effect would be more pronounced to anterior rectal

27

IMAGING MODALITIES

cancer, presumably because there is a greater depth of tissue anterior to the

presacral fascia(Kim et al.,2004).

Figure (12):(a,b) Axial T1-weighted image of pelvis at level of sacro-coccygeal junction in patients with

(a) and without (b) administered rectal gas. Measurements from rectal wall to mesorectal fascia are

demonstrated(Slater et al.,2006).

Patient position

The patient is positioned comfortably on the back. Phased-array surface coil is placed on the pelvis in such a way that the lower

edge of the coil comes to lie well below the pubic bone(Klessen et al.,).

Hardware

Magnet

A 1.0 T/1.5 T system can be used. The main consequence of using a 1.0T/1.5 T magnet is the longer image acquisition times. Using 1.5 T magnet, the totalexamination time required for good image resolution is about 45-65 minutes, thisproblem can be overcome with a 3 T MRI system because the increase in signal-to-noise ratio (SNR) at 3 T can decrease the number of signals averaged, so theexamination time is quite a bit shorter ranging from 19 to 22 minutes. In addition,

28

IMAGING MODALITIES

the higher SNR can improve spatial resolution and allow acquisition of thinnersections. However, SNR is not solely determined by magnetic field strength, thusoptimization of the imaging parameters and improvement of phased-arrayradiofrequency coils are important for maximal SNR in body imaging(Chun etal.,2006). (Brown et al.,2005).

Coil choice :

Conventional external body coils are unable to provide adequate bowel wall

assessment, having similar overall accuracies to CT (Brown et al.,2005).

Phased array coils :

Rectal MR imaging with a phased-array surface coil yields high-spatial-

resolution images, thereby providing a full evaluation of the rectal wall layers, and

has the additional advantage of a large field of view. Moreover, the use of a

phased-array surface coil improves patient comfort compared with the use of an

endorectal coil. Finally, stenosing lesions and tumors at the rectosigmoid junction

can be evaluated in all cases, and the mesorectal fat and mesorectal fascia can be

visualized (Figure 33) (Laghi et al., 2002).

29

IMAGING MODALITIES

Figure (13): Rectal adenocarcinoma. Sagittal turbo spin-echo T2-weighted MR image obtained with a high-resolution phased-array surface coil shows a stenosing lesion (arrow) of the rectal lumen (*). This lesion isoutside the potential field of view of endorectal US and endorectal coil MR imaging (Laghi et al., 2002).

Endorectal coils:

Surface coils, such as the endorectal coil (fig.34), are designed to maximize

signal return from the small area being imaged. These coils comprise an oval

receive only loop coil mounted on the inner surface of an inflatable balloon and

have the advantage of placement against the surface of the tissue being imaged

such as the rectal wall. A gap of several millimeters is present between the surface

of the coil and the surface of the lesion and the balloon needs to be distended in

order to maintain the position of the loop coil close to the primary tumor(Brown etal.,2005).

The coil design permits improved SNR, allowing image acquisition using a

smaller field of view and thinner slices. Thus endorectal MRI provides high-

resolution images that depict bowel wall layers fully, however, clear differentiation

between mucosa and submucosa is still difficult. Studies comparing endorectal

MRI and transrectal ultrasound for staging superficial tumors have shown the two

techniques to have comparable accuracy(Brown et al.,2005).

30

IMAGING MODALITIES

Limitations:

There are limitations related to the use of any endoluminal technique in

which stenosis, stricturing, pain and discomfort, bowel wall motion, difficulty

placing the probe in the upper rectum and coil migration all hamper image

acquisition.

Small volume of sensitivity; The area that can be imaged using such coils

amounts to a total distance of one coil diameter away from the coil with a very

rapid drop in signal intensity beyond the immediate vicinity of the coil. Reports

have showed poor resolution of pelvic structures surrounding the rectum, such as

mesorectal fat, mesorectal fascia, and lymph nodes outside the field-of-view.

These are significant limitations of using an endoluminal technique and

therefore such devices are not recommended in the routine staging of rectal

cancer(Brown et al.,2005)

31

IMAGING MODALITIES

Figure(14): (a,b) (a) Endorectal coil. (b) T2 weighted image using the endorectal coil. The bowel walllayers are shown but there is insufficient detail from the surrounding mesorectum to adequately stage

rectal tumors(Brown et al.,2005).

Pulse sequences

The initial sagittal T2 scans are used to plan the thin section weighted

oblique axials (Figure 35) (Brown, 2005).

Figure (15): The sagittal T2 weighted scans are used to plan thin-section axial oblique scans. It is important toensure the scans are obtained in a plane orthogonal to the tumour to prevent over-estimation of tumour spread

(Brown, 2005).

For tumours arising below the level of the levator origins (<6 cmfrom theanal verge), it is essential to undertake high resolutioncoronal or paracoronalimaging (Figure 36) and to evaluatethe sagittal images carefully, as well as thestandard obliqueaxial sections, in order to avoid the common pitfall of

overestimating betumour spread into the levator muscles. In addition, care musttaken to plan scans orthogonal to the rectal wall in orderto avoid problems withpartial voluming(Brown, 2005)

32

IMAGING MODALITIES

Figure (16): For tumours arising below the origin of the levator muscle, scans are obtained in a coronal orparacoronal plane as shown (Brown, 2005)

To adequately assess the nodal status, scans must include themesorectum

above the tumour, as nodal spread will be in a cranialdirection within the

mesorectum. Inadequate coverage will leadto understaging. For the lower third

rectal tumours, the restof the mesorectum can be staged for nodes by planning a

block (Brown,of paracoronal slices that run parallel to the sacrum (Figure37)

2005)

33

IMAGING MODALITIES

Figure (17): Scan planes used for assessing mesorectal lymph nodes. The mesorectum can be assessed forlymph nodes by planning a block of coronal slices that run parallel to the sacrum (Brown, 2005).

High-resolution T2-weighted TSE sequence with a small FOV and a slice

thickness of 3 mm. It is mandatory to place the slices perpendicular to the

longitudinal axis of the tumor or the intestinal lumen in the vicinity of the tumor.

With this sequence, it is possible to precisely evaluate the tumor, mesorectal fascia

and mesorectal lymph nodes(Klessen et al.,2007). For visualization of more distant lymph nodes a T1 to proton-density-weightedtwo-dimensional (2D) TSE sequence in axial orientation with a slice thickness

5 mm which covers the entire area up to the aortic bifurcation can be used.

Alternatively, a T1-weighted 3D gradient-echo sequence can be used for this

purpose, allowing for the reconstruction of thinner slices(Klessen et al.,2007). Since differentiation with the T2-weighted sequences is based on the contrast

between the high-signal-intensity mesorectal fatty tissue and the rather low signal

intensity of the tumor, spectral fat suppression techniques are not needed. The

duration of the MRI protocol as just outlined is about 25-30 min, including

planning (Brown et al.,2005). 3D MR imaging cannot replace 2D MR imaging for local staging of rectal

cancer. High-resolution 2D T2-weighted MR images yielded superior results with

regard to rectal wall layer visibility and prediction of muscularis propria invasion

compared to 3D T2-weighted MR imaging, (3D)-data sets are time consuming, and

sensitive for motion and susceptibility artifacts. Perirectal tissue invasion was

adequately visualized with both 2D and 3D techniques with almost similar results.

3D MR imaging can be used for visualization of the complex pelvic anatomy for

treatment planning purposes(Futterer et al.,2008).

34

IMAGING MODALITIES

Whole-body MRI: The recent introduction of powerful whole-body MRI systems

enables imaging of the whole body in a single session through repeated table movement.

Several studies have already demonstrated the benefit of this approach for a variety of

diagnostic queries in oncologic patients. This technique may be used for rectal cancer

staging in the future allowing for local staging and whole-body staging in a single

session(Schmidt et al.,2005).

Major disadvantages of whole-body MR coverage in the past have been long

examination times caused by time-consuming patient repositioning processes and

changing of the array configuration. In addition, it was difficult to integrate the

different anatomic regions to be examined into a single comprehensive scan.

Recent improvements in hard- and software, had substantially reduced the

individual scan times, resulting in shorter overall examination times without

compromising spatial or temporal resolution. Now, dedicated assessment of

individual organs by sequences with various soft tissue contrast, image orientation,

spatial resolution, and contrast media dynamics can be combined with whole-body

anatomic coverage(Schmidt et al.,2005).

35

IMAGING MODALITIES

Figure.(18): Overview of the applied sequences on a whole-body magnetic resonance protocol for a 32-receiver channel scanner (Magnetom Avanto; Siemens Medical Solutions, Erlangen, Germany). Total

scan time is 55minutes (Schmidt et al., 2005).

Potential factors that may impair the quality of images

Coil positioning

In order to prevent poor signal to noise ratio from the anorectal junction, it is

important that the phased array coil is centered optimally from the level of the

sacral promontory to below the symphysis pubis

(Brown et al., 2005).

36

IMAGING MODALITIES

Figure(19):Poor coil positioning. The images shown (top left and right) have been obtained with thelower edge of the pelvic coil placed at the level of the symphysis pubis. Consequently there is poor signalto noise ratio from the lower rectum and anal sphincter region. Repositioning the coil restores adequate

signal to noise ratio (Brown et al.,2005

Figure (20): It is important to centre the coil correctly to the whole rectum. Thus the

37

IMAGING MODALITIES

lower edge of the coil needs to be placed so that it lies at least 10cm below the symphysis pubis in orderto ensure adequate signal is obtained from the lower rectum and anorectal junction. The uppermost limit

for coil placement is the sacral promontory (Brown et al., 2005).

Choice of sequences

T1 weighted imaging:

Although the availability of short repetition time/echo time (TR/TE) volumeimaging can provide images of high spatial resolution, images obtained fail to

depict either tumor or the layers of the bowel wall due to similar relaxation rates oftumor and bowel wall.(Brown et al.,2005)

Figure (21): A T1 weighted image has been obtained with a high spatial resolution but the bowel wall

layers cannot be distinguished (Brown et al., 2005).

Fat saturation and contrast enhancement:

A contrast enhanced technique requires the high signal from surrounding perirectal

fat on T1 weighted images to be suppressed to permit visualization of high signal

enhancement of tumor. This results in a further reduction in signal to noise ratio and

potential overstaging of tumors due to enhancement of adjacent non-tumor tissue

namely vessels, desmoplastic reaction and normal nodes (Brown et al., 2005).

38

IMAGING MODALITIES

Figure(22):T1 fat saturated image with contrast enhancement. The bright fat signal intensity fromperirectal fat (asterisk) has been suppressed and is of low signal intensity, there is florid enhancement ofthe entire bowel wall (arrow) and perirectal vessels (arrowheads) which would not be readily

distinguishable from tumor if it were present(Brown et al.,2005).

Tumor not seen on initial sagittal sequences:

On occasion, lack of clinical detail or the presence of a small tumor prevents

the tumor being seen on the sagittal images. In these instances, tumor may only be

visible on the high resolution images. In order to ensure that the tumor has not

been missed it will be necessary to perform high resolution scans along the entire

length of the rectum(Brown et al.,2005).

Patient unable to tolerate long scan:

Some patients (5%), either due to co-existing medical conditions or

claustrophobia, find the scan impossible to tolerate; a combination of

patient discomfort, excessive motion of the anterior abdominal wall may

result in motion artifact. This is seen as horizontal bands across the image. Of all of

39

IMAGING MODALITIES

the sequences the oblique high resolution scans are the most important. The sagittal

views can be shortened by altering the parameters; the large field of view axials are

performed last and may even be omitted if the patient is inconsiderably

discomfort(Brown et al.,2005).

Figure(23):(a,b) Motion artifact. (a) This characteristically produces a series of bands that degrade theimage. (b)This can often be overcome by ensuring the patient is not in discomfort, by repositioning thepatient and ensuring adequate abdominal compression and repeating the sequence again after swapping

phase and frequency directions(Brown et al.,2005).

Magnetic resonance imaging has inherent limitations with foreign bodies that areMRI incompatible. Foreign bodies that are compatible, such as surgical clips, mayalso obscure images (Skandadajah et al., 2006)

Has been shown to be mandatory in preoperative local staging.

40

IMAGING MODALITIES

Fig (24) Sagittal turbo spin-echo T2-weighted MR image obtained with a high-resolution

phased-array surface coil shows a stenosing lesion (arrow) of the rectal lumen (*).FrancoIafrate.et al. (2006).

41

Imaging Manifestations

MR Imaging Manifestations of RectalCancer

The identification and staging of rectal cancers at MR imagingis largely based

on differences in T2 signal intensity betweenthe tumor, the mucosa and submucosal

layers, the muscular layer,the perirectal fat, and the mesorectal fascia. The perirectal

fat has high signal intensity on turbo spin-echo T2-weighted images and surrounds the

low-signal-intensity muscularis propria.The tumor itself has an intermediate signal

intensity betweenthe high signal intensity of the fat tissue and the low signal

intensity of the muscular layer. Furthermore, its signal intensity is higher than that of

the mucosal and submucosal layers (Figure 25) (Iafrate et al., 2006).

Figure (25): Rectal carcinoma. Coronal turbo spin-echo T2-weighted MR image shows a stage T1 tumor (*)of the rectum. The tumor has an intermediate signal intensity between the high signal intensity of the fattissue (jagged line) and the low signal intensity of the muscular layer (black arrow). The inner layer of therectal wall (white arrow) consists of mucosal and submucosal layers and has high signal intensity (Iafrate etal., 2006)

42


The mesorectal fascia appears as a thin, hypointense line surroundingthe

hyperintense perirectal fat. However, the spatial resolutionof phased-array surface

coil MR imaging is not adequate to allowdifferentiation between the mucosal

and submucosal layers ofthe inner layer (Iafrate et al., 2006).

MR tumor radiological appearance

Exophytic or polypoidal tumors are shown as intermediate signal intensity,

rounded, protuberant mass lesions that project into the lumen. The surface of these

polypoidal tumor mass lesions often shows high signal intensity clefts

corresponding to mucinous fluid on the tumor surface(Martling et al.,2003).

Figure(26): High-resolution T2-weighted image demonstrating a T1 polypoid carcinoma (arrow). Thereis partial preservation of the submucosal layer (short arrow) seen as a thin rim of high signal intensity

deep into the tumor. The tumor does not extend into the muscularis propria layer(Martling etal.,2003).

43


Rectal tumors are most commonly demonstrated as an elevated plaque of

intermediate signal that projects into the lumen forming a U-shaped thickened disc

corresponding to an annular or semiannular plaque of tumor on histologic

sections(Martling et al.,2003).

Figure(27):Axial T2-weighted FSE MR image demonstrating a semiannular plaque of tumor with centralulceration (arrowhead) and raised rolled edges (arrows) (Martling et al.,2003).

T staging criteria on MR imaging:

T0:Normal rectal wall layers, no visible tumor.

T1:Mucosa and submucosa affected, no extension beyond the

hypointense layer of muscularis propria.

T2:Hypointense layer of muscularis propria invaded, no extension to serosal and

perirectal fat.

T3:Invaded perirectal fat.

T4:Tumor signal intensity extends into an adjacent structure or viscus(Donmez etal.,2008).

44


In T1, the tumor signal intensity is confined to the submucosal layer and has

relatively low signal intensity compared with the high signal intensity of the

surrounding submucosa(Klessen et al.,2007

Figure (28): Stage T1 rectal carcinoma. Coronal turbo spin-echo T2-weighted MR image shows a hugepedunculated tumor (T) on the left lateral rectal wall. The integrity of the muscular layer (arrow) appearsnot to be disrupted. The mesorectal fat (*) has a homogeneous appearance without tumoralinvolvement.The mesorectal fascia (arrowheads) is also well depicted (Iafrate et al., 2006)

Table (4) illustration of T-stage of rectal cancer.Max Lahaye. et al. (2010).

45


Figure (29): Stage T1 rectal carcinoma. Coronal turbo spin-echo T2-weighted MR image shows the tumor(T) invading the rectal wall without infiltrating the perirectal fat (arrow). In this imaging plane, thedistance of the tumor from the plane of the levator ani muscle (L) and from the anal sphincter complex (A)can easily be evaluated (Iafrate et al., 2006)

Figure (30): Stage T1 rectal carcinoma.Axial turbo spin-echo T2-weighted MR image shows a polypoidtumor (T) on the right lateral aspect of the rectal wall protruding into the rectal lumen. It is difficult todetermine whether the muscular layer (arrow), which appears thinned, is infiltrated or spared (Iafrate et al.,2006).

46


In T2, the tumor signal intensity extends to the muscle layer, leading to

irregularity or thickening of the muscle layer, but without perirectal tissue

invasion, the outermost margin of the muscularis propria will remain intact with

stage T2 tumors or less (Klessen et al.,2007).

Figure (31):Stage T2 rectal carcinoma. Coronal T2-weighted MR image shows a stenosing neoplasticlesion (*) of the rectal lumen involving the mucosal, submucosal, and muscular layers. The muscularlayer is visible as a continuous hypointense line, and no neoplastic spread into the mesorectal fat (arrow)is seen. The major criterion for differentiating between stage T2 and stage T3 tumors is the presence of

neoplastic tissue within the mesorectal fat(Iafrate et al 2006).

Figure (32): Stage T2 rectal carcinoma. Unenhanced T2-weighted fast spin-echo image Showsmesorectal fascia (arrowheads) as fine linear hypointense structure enveloping mesorectum. Tumor

(T) is revealed as being confined in muscularis propria(mp) Akasu et al., 2005).47


The major criterion for differentiating between stage T2 and stage T3tumors is the presence of neoplastic tissue within the mesorectal fat. In

differentiating isbetween stage T2 and stage T3 tumors, the crucial criterioninvolvement of the perirectal fat, which is characterizedby the in ability tovisualize the interface between the muscularlayer and the perirectal fat, with arounded or nodular advancing margin (Iafrate et al., 2006).

In stage T3 tumors, the muscularis propria is totallydisrupted and cannot beclearly distinguished from the perirectal 2fat (Figure 33 ) (Iafrate et al., 006).

Figure (33): Stage T3 rectal cancer .Transverse contrast material-enhanced T1-weighted turbo spin-echoMR image shows rectal tumor (black arrow) with transmural stranding (arrowheads) in mesorectal fat.Mesorectal fascia (white arrows) is clearly depicted (Beets et al.,2001).

In T3, the tumor signal intensity extends through the muscular layer into the

perirectal tissue, or angiolymphatic tumor invasion (irregularly thickened strands)

present in the mesorectum. The appearances of nodules (figure(34), an interruption

of the outer wall of the rectum or an irregularly thickened spiculations(Klessen etal .,2007).

48


(b) (a)

Figure(34)(a,b) (a) Axial high-resolution T2-w image showing a tumor with a pushing edge. Theadvancing edge of the tumor has a well-circumscribed margin with a sharp border between the advancingedge of the tumor and the perirectal fat. This is the most common pattern of tumor spread. (b) Axial T2-wFSE image showing nodular extension with ill-defined margins. The tumor is spreading into the perirectal

fat at its leading edge(Martling et al.,2003).

fine spiculations which cannot be considered as a reliable sign for the

presence of extramural invasion as it can be caused by fibrosis, are considered to

be indicators of the T3 stage on MRI. A further feature that may lead to incorrect

diagnosis is that of small interruptions of the outer contour of the muscle coat,

which may incorrectly stage the tumour as T3 (Chun et al.,2006).

Any isolated tumor deposit in the immediate perirectal space, measured to

be within 3mm of the bowel wall and with the same MRI signal as the primary

tumor, can be interpreted as extramural spread.

49


Tumor deposits further than 3mm from the bowel wall can be assumed to

represent metastatic spread. Tumor deposits of more than 3mm in size are

considered as involved lymph nodes even if no lymphoid tissue was present.

For T3 tumors with disease-free circumferential margins, it was shown that

> 5 mm spread of tumor beyond the bowel wall predicts a significantly poorer

survival than < 5 mm spread (54% compared to 85% respectively)

(Matthhew,2008)

Circumferential resection margin (CRM):

The most important predictor of local recurrence is CRM infiltration and

tumor mesorectal fascia distance. The actual T staging system does not

differentiate between tumors with a wide CRM and those with a narrow

CRM(Iafrate et al.,2006).

Figure(35). Drawing illustrates the relationship between the CRM and rectal tumors of various stages.The actual T staging system does not differentiate between tumors with a wide CRM (T3⌂) and thosewith a narrow CRM (T3*). Of these stage T3 tumors, the latter poses a higher risk for recurrence. At MRimaging, it is important to be able to identify patients with infiltrating tumors that have a narrow CRM

50


or that infiltrate the mesorectal fascia who might benefit from neoadjuvant treatment. T1 = stage T1tumor, T2 = stage T2 tumor, T4 =stage T4 tumor, Ves = vesicle(Iafrate et al.,2006).

The expected CRM can be described as involved if tumor invasion of the

mesorectal fascia is visible or the tumor has a proximity of 1 mm or less to the

mesorectal fascia. Actually there has been a debate whether the distance of CRM

‘≤ 1mm’ or ‘≤ 2mm’ should be regarded as the involved CRM. In recent years, ≤

2mm definition of CRM became widely accepted. A tumor-free CRM can be

assumed with a high degree of accuracy if the shortest distance from the maximum

tumor extension, a mesorectal tumor deposit or a suspect lymph node in the

mesorectum is more than 6 mm(Klessen et al 2007).

Figure(36):CRM is safe if distance of tumor to mesorectal fascia is >6mm(Smith and Brown2008)

51


Histological analysis demonstrated that a tumor-free resection margin of

2 mm was predicted if the distance between tumor and mesorectal fascia measured

by MRI was at least 6 mm. Tumors that extend towards the mesorectal fascia to a

distance of less than 5 mm on MR images remains controversial(Kim et al.,2008).

Figure(37):Transverse T2-weighted MR image of the middle of the pelvis. The tumor (double-headedarrow) in the right lateral anterior aspect of the rectum shows extramural extension, with a minimumdistance to the mesorectal fascia (white arrows) of 5mm(Beets-Tan and Beets 2003).,

MR imaging is a highly accurate and reliable techniquefor the prediction of

CRM infiltration and thus represents anoninvasive tool for identifying those patients

who may benefit whofrom preoperative chemotherapy or radiation therapy and those

should undergo TME (Iafrate et al., 2006)

CRM is closely related to a high recurrence rate aftersurgery (Figure 38)

(Brown, 2004).

52


Figure (38): Stage T3 tumor with involvement of the mesorectal fascia. Coronal turbo spin-echo T2-weightedMR image shows a neoplastic rectal lesion infiltrating the mesorectal fat and involving the mesorectalfascia(arrowheads), which appears thickened. The mesorectal fascia represents the surgical resectionmargin. Patients with this kind of tumor benefit from preoperative neoadjuvant therapy to reduce thepostoperative local recurrence rate (Brown , 2004).

Vascular invasion of a rectal carcinoma is associated with an increased rate

of local recurrence and is considered as an important independent prognostic

factor. The typical appearance on MRI, which is the only imaging modality that

has been shown to demonstrate extramural vascular invasion (EMVI) in rectal

cancer is that of discrete serpiginous or tubular projections of intermediate signal

intensity into perirectal fat, following the course of a visible perirectal vessel

(usually a vein). The sensitivity and specificity of MRI for detecting EMVI was

62% and 88% respectively. Some patients with microscopic vascular invasion

could not be resolved on MRI, while others with very obvious EMVI on the pre-

operative images had false-negative histo-pathology due to obliteration of normal

53


venous architecture which makes it difficult for the pathologist to recognize that a

tumor deposit lies within the course of a vessel, something which may be more

readily appreciated on serial MR images((Smith and Brown 2008).,

Figure(39):Extramural vein invasion(Jemal et al.,2007).

Figure(40): rectal carcinoma with EMVI.AxialT2 weighted image showing tumor extending into anextramural vein. There is serpiginous extension of the tumor into the perirectal fat (arrow) following a

presumed vessel that was shown histologically to be thick-walled extramural venous invasion(Burtonet al 2006).

54


In stage T4 tumors, the signal intensity of the tumor is seeninfiltrating

surrounding structures (ie, other organs and muscularstructures of the pelvic wall

(Figure 60) (Iafrate et al., 2006)

Figure (41): Stage T4 tumor. Axial turbo spin-echoT2-weighted MR image shows a neoplastic rectallesion (arrow) disrupting the mesorectal fascia. Tumoral infiltration of the seminal vesicles (*) is alsoevident Iafrate et al., 2006).

Figure(42):(a,b) (a) Paraxial T2-weighted FSE sequence and (b) sagittal T2-weighted FSE sequence ofa T4 cancer located in the upper third of the rectum invading the uterus (arrows) (Klessen etal.,2007).

55


Figure(43):Sagittal T2-w turbo spin-echo MR image in same patient clearly shows that tumor originatesfrom the rectum (black arrows). Although tumor extends on the dorsal wall to the presacral fascia (arrowheads), on the ventral wall it is limited to the rectal wall. Hypointense line (white arrows) between tumorand uterus is a composition of uterine wall, peritoneum, mesorectal fascia, and rectal wall and indicatesthat tumor has not yet invaded the uterine body( Beets et al., 2004).

Pitfalls :

Poor differentiation between T1 and T2 tumors, however, in most casesthese tumors are both treated with TME-surgery, so it is not necessary to make thedifference. In a minority of cases a T1 tumor is treated with local excision, in thesecases endorectal US is accurate for staging these superficial tumors(Lahaye et al.,2010).

Differentiation between T2 and T3 tumors may be difficult with MRI andover-staging is often caused by perirectal desmoplastic reactions which do notcontain tumor cells(Lahaye et al., 2010).)

To be on the safe side and to avoid understaging, it is advised to stage

tumors with perirectal stranding as T3 tumors. For therapeutic purposes it does not

have any consequences to differentiate accurately between a T2 CRM- and a T3

CRM- tumor, both tumors will be treated with a preoperative low dose

56


radiotherapy followed by TME. Understaging can also occur due to microscopic

invasion of perirectal fat(Chun et al .,2006).

Figure(44)(a,b,c) Difficulty in interpretation of tumor penetration of rectal wall. (a) On this transverseGd-enhanced T1-w image, enhancing spiculations (arrows) are seen in mesorectal fat, suggesting tumorpenetration of rectal wall (stageT3). However, histologic examination showed that these spiculationsconsisted of fibrosis without tumor cells (stageT2). (b) On this transverse gadolinium-enhanced T1-wimage in a different patient, enhancing spiculations (arrows), indistinguishable from those in a, are seen inmesorectal fat. In this case, spiculations consisted of fibrosis and tumor cells (stageT3). Spiculationsconsisting of fibrosis either with or without tumor cells cannot be discriminated on non enhanced orgadolinium-enhanced MR images. (c) Clear invasion of mesorectal fat. Coronal T2-w TSE MR of tumorwith pattern of nodular infiltration (arrows) of mesorectal fat in a different patient. Nodular advancingtumor margin is highly predictive for tumor penetration of rectal wall, as opposed to margin consisting ofspiculations (a, b)(vliegen et al.,2005).

in low bulky tumors, the fat plane between the tumor and the adjacentstructures can be obliterated because of the mass effect of the tumor. In these

57


circumstances, it can be difficult to distinguish compression of adjacent organs(posterior vaginal wall (fig64), seminal vesicles, prostate, bladder from tumorinvasion into these organs Vliegen et al.,2005).

Fig.(45).Transverse T2-weighted TSE MR image of bulky (voluminous) low anteriorly located tumor.This tumor (T) causes a mass effect on surrounding pelvic structures (arrow heads indicate vagina) andstretches fat plane in-between these structures. When surrounding pelvic organs have normal signalintensity, it can be difficult to differentiate compression from tumor invasion. In this case, histologic

Vliegen et al.,2005). )examination showed invasion of vagina. B=bladder

Assessment of sphincter involvement :

MRI showed 98% specificity and 100% sensitivity for the assessment of

sphincteral involvement. The prediction of a tumor free anal sphincter allowed to

successfully planning a sphincter saving surgery in most patients. The sphincter ani

cannot be saved with less than 1cm minimal distance between the tumor and

dentate line(Winter et al.,2007).

Conversely, the knowledge of the depth of sphincteral involvement did not

influence treatment because there is a policy is to resect all tumors with sphincteral

infiltration by means of abdomino-perineal resection, irrespective of the extent of

infiltration. However, in such a case others proposed an intersphincteric resection

with colo-anal anastomosis provided that the striated sphincters are not

infiltrated(Ferri et al.,2005).

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Figure(46).Rectal adenocarcinoma with involvement of the sphincter. Coronal FSE T2-w MR imageshows a tumor (T) of the rectal ampulla causing stenosis of the rectal lumen and infiltrating thesphincteral plane, which is composed of the internal muscular sphincter (*) and the external sphincter

(ES). The levator ani muscle (L) is also evident and appears to be uninvolved(Iafrate et al.,2006).

mucinous carcinoma

On T2-w images, rectal carcinomas appear as wall lesions exhibiting signalintensity slightly higher than the muscularis propria but lower than the submucosa.High signal intensity of the tumor on T2-w images higher than that of thesubmucosa suggests the presence of mucinous carcinoma (parts of the mucouslakes) that is isointense to fluid within the layers of the rectal wall, and the layerscan typically show high signal intensity expansion (fig.66) (Klessen et al.,2007).

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Figure (47): Staget3 rectal mucinous adenocarcinoma. Transverse T2-weighted turbo spin-echo MRimages show hyperintense rectal tumor (arrowheads) extending to mesorectal excision plane on anteriorand left lateral sides (arrows). The hyperintense nature of the lesion on T2-weighted images is

characteristic of mucinous tumor ( Beets et al.,2004).

Figure(48):Axial T2-w FSE MR image demonstrating a mucinous tumor characterized by very high

signal intensity (high water content). The tumor (asterisk) infiltrates the bowel wall without destroying

the boundaries between the individual layers, resulting in accentuation (thickening) of the bowel

wall(Klessen et al.,2007).

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It is suggested that MRI can help distinguish between mucinous and non mucinous

carcinomas (fig.49).

In some cases where the tumor extended outside the rectal wall, its

extrarectal components were composed largely of mucin pools. Moreover, this

perirectally extended mucin-containing tumor would be difficult to observe during

surgery if it had not been noticed preoperatively, which may contribute to the

relatively high rates of local failure compared with nonucinous tumors. (Kim et al.,

2003)

Figure(49).(a,b,c) 57-year-old woman with a mucinous carcinoma. (a)The axial FSE T2-w image depicts

a large area of hyperintensity extending to the perirectal space, ssuggestive of a mucin pool (arrow).(b)On the axial T1-weighted image, the tumor shows signal intensity similar to the normal rectum or

muscles. (c)CoronalT2weighted image show the tumor extending into the perirectal fat plane(Kim etal.,2003).

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Possible causes of false diagnosis can result from the false positive

interpretation of areas of high signal intensities mimicking mucin pools

innonumcinous carcinomas, such as intratumoral congestion, abscess, necrosis, and

mural edema (fig.69) in the adjacent rectal wall or entrapped fluid between the

tumor and the adjacent rectal wall. These areas are relatively small and scarce

within the tumor or located mainly outside of the tumor, or can result from false

negative diagnosis due to ignoring small mucin pools that were deemed to be

insignificant. The portion of the mucin pools that was missed at MRI or the high

signal intensity that was falsely interpreted as a mucin pool usually comprised only

a small portion of the tumors (Kim et al, 2003)

Additional use of gadolinium enhanced sequences may improve radiologists

ability to different between a mucin pool and edema, necrosis, or abscess because

the tumor mucin pool may be enhanced, whereas the others do not enhance.

However, studies show that unenhanced images alone showed high accuracy for

the differentiation of mucinous and nonmucinous tumors (Kim et al., 2003)

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Figure(50).(a,b) 70-year old woman with a nonmucinous carcinoma. Sagittal (a) and coronal (b) FSET2-w images. The areas of the high signal intensity of submucosal edema in the adjacent rectal wall canbe misinterpreted as a mucin pool (arrow heads) and render a false-positive diagnosis of mucinouscarcinoma. Correct identification of a nonmucinous tumor narrowing a segment of the rectum (arrows)

can be made if the extratumoral location of the high signal intensity was correctly identified(Kim etal.,2003).

N staging :

The majority of involved lymph nodes in patients with primary rectal cancer, as

depicted on preoperative MRI are located at tumor height or above, in the

dorsolateral compartment of the mesorectum (fig.70). Involved nodes distal to the

tumor are not common. Involved extramesorectal nodes are also not common

(fig.71) and occur mainly in patients with distal rectal cancer with nodal metastases

in the mesorectum (Engelen et al.,2008).

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Figure(51):.Axial T2-weighted fast spin-echo MR image. There is a large lymph node located outside

the mesorectal compartment (white arrow), in the region of the middle rectal artery. The node is located

at same height as the tumor(R). There are also nodes located in the mesorectum (black arrows).U=

uterus(Engelen et al.,2008).

Figure.(52)Axial T2-weighted FSE sequence. Inguinal lymph node metastases (arrows) in a patient with

low rectal cancer(Klessen et al.,2007).

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N staging criteria on MR imaging:N0: <5mm, of any number.

N1: >5mm, less than 4 in number, in perirectal area.

N2: >5mm, more than 4 in number, in perirectal area.

N3: metastases in any node along the course of a vascular trunk or in apical

node(Donmez et al.,2008).

Table (5) Illustration of N-stage of rectal cancer.Max Lahaye. et al. (2010).

Diagnostic criteria on MR imaging

1- SIZE :

Lymph node size is not a reliable criterion for metastatic involvement

(fig.72). There is no consensus as to the exact cut-off size, some authors regard any

visible node in the perirectal fat as positive, while others employ size criteria with

cutoff values for nodal positivity that range from 3 to 10 mm(Brown et al.,2003).

65


Figure (53): Rectal adenocarcinoma with metastatic lymphadenopathy. Coronal turbo spin-echo T2-weighted MR image demonstrates a rectal tumor (*) and two enlarged lymph nodes within themesorectal fat (arrowhead) (Kim et al., 2004).

Figure(54):.False-negative diagnosis was made in a 57-year-old man with microscopic tumor cells in aregional LN. A T2-W axial image shows a shallow ulcero-infiltrative lesion (black arrow) in theposterior rectal wall. The depth of invasion is confined to the muscular layer. A 3-mm peritumoral LN

(white arrow) is seen in the 5-o’clock direction(Koh et al.,2004).

2- Border :

nodal involvementdetermined on the basis of irregular borders and signal

intensityor characteristics. They concluded that the presence of spiculated

66


indistinct node borders and a mottled heterogeneous signalintensity pattern

might help predict nodal involvement (Figure 74) (Kim et al., 2004)

It is well recognized that partial or complete nodal replacement with

a tumor results in gross distortion, and extranodal extension in incompletely

involved nodes leads to irregularity of the surrounding capsule. The high spatialresolution of the MR imaging technique in assessing this feature, combined withthe heterogeneity of the intranodal signal intensity, produces a powerful predictorof lymph node status that shows good reproducibility between observers and isindependent of, and greatly superior to lymph node size(Brown et al.,2003).

a

Figure(55):.(a,b) (a) T2-w FSE transverse MR image through the upper portion of the rectum. A nodewith an irregular border (arrow) located close to the right lateral mesorectal margin contains mixed signalintensity.

(b)T2-w FSE transverse MR image through the middle portion of the rectum. A high-signal-intensitynode with smooth borders (arrow) of homogeneous signal intensity is demonstrated close to the rightposterolateral border of the mesorectum. Corresponding histologic examination revealed benign

node(Brown et al.,2003).

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3- Signal Intensity :

Internal morphology of normal nodes is best demonstrated on T2-weightedimages. It is a common misconception that all lymph nodes of high signal intensitycontain fat. While fat replacement of nodes is well recognized in the axilla andinguinal nodes, the presence of intranodal fat is not a feature of perirectal lymphnodes. The high signal intensity is presumed to represent fluid within lymphoidfollicles, and are surrounded by a low-signal-intensity capsule(Brown et al.,2003).

The demonstration of intranodal heterogeneity of signal intensity (ie mixedsignal intensity) is shown to be a highly specific discriminant. However, if usedalone as a marker for nodal involvement it results in a low sensitivity(Brown etal.,2003).

Evaluation of intranodal signal intensity homogeneity requires high-quality imagesthat are free of movement artifacts, also and because these qualities are difficult toobtain in small nodes, we do not feel able to make this assessment in nodes lessthan 3 mm(Brown et al.,2003)

Figure(56):.Identification of lymph nodes at transverse T2-weighted MR imaging. Axial image showstwo intermediate-signal-intensity lymph nodes (arrows) in right mesorectum. Vessels are readily

distinguished from nodes as low-signal-intensity tubular structures (arrow heads) (Koh et al.,2004).

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Figure (57): Rectal cancer with involved lateral node outside mesorectum. Transverse T2-weighted turbospin-echo MR image shows enlarged, round, hyperintense lymph node (arrowheads) in left hypogastricregion in, suggestive of a metastatic node. This node is located outside the mesorectum, and with standardTME it would be left behind. Such nodal involvement can be a risk for local recurrence ( Beets et al.,2004).

Figure(58)T2-w FSE transverse MR image shows a node of mixed signal intensity with a low-signalintensity rim (arrow head). A focus of low signal intensity (arrow) is demonstrated within thepredominantly intermediate-signal intensity node. Histologic slice shows low-signal-intensity rim tocorrespond to the normal lymph node capsule (arrow head).Within the node, there is tumor with widespread necrosis in the area corresponding to the low-signal-intensity area seen on the MR

image(Brown et al.,2003).

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Real improvement in lymph node characterization willcome with the use of ultra-

small iron-based particles. Theseparticles are selectively taken up by the reticulo-

endothelialcells in normal lymph nodes, which thus have low signal intensityon

proton-density-weighted and T2-weighted MR images.Pathologic lymph nodes, with

reticuloendothelial cells replacedby neoplastic cells, will not take up the contrast

agent andthus will have a relatively bright signal intensity. (Bellin et al., 2000).

Uspio- enhanced MRI

A new promising approach to detect metastatic lymph nodes using

ultrasmall superparamagnetic iron oxide particles (USPIO) as a contrast medium

for systemic MR lymphography(Lahaye et al.,2008).

Dose: The USPIO MR Contrast agent consists of low-molecular-weight iron oxidecoated with dextran, supplied as a powder in a glass vial containing 210 mg, andmust be reconstituted by using 10 mL of normal saline. A dose of 0.13 mL/kg ofbody weight (2.6 mg of iron per kilogram) of the reconstituted solution is to bediluted in 100 mL of normal saline. The contrast agent is given intravenouslywithin a period of approximately 45 minutes by means of a slow-drip infusion witha microfilter. Administration is closely monitored for any adverse effects and iscompleted 24-36 hours before contrast material-enhanced MR imaging is carriedout(Lahaye et al.,2008).

The nanoparticles cause a decrease in signal intensity (SI) within the node

Variation of SI within a node can be explained on the basis of the concentration of

macrophages (nanoparticles) in a particular region in the node. A region with a

normal concentration of macrophages (nanoparticles) will produce an area with SI

decrease on T2- and T2*-weighted images The involved part of the lymph node70


will show no SI decrease caused by the replacement of macrophages by tumor

cells, creating a region of increased SI within the node (white region)( Lahaye etal.,2008).

The percentage of white region within the node on USPIO-enhanced T2*-weighted MR images either by visual assessment or through quantitative

measurement by dividing the surface area of the white region by the surface area ofthe total node determined on a transverse image where the node was the largest bymeasurement tools of the workstation(Lahaye et al.,2008).

Estimated area of white region within the node that is larger than 30% is

highly predictive for an involved node, with a sensitivity of 93% and a specificity

of 96%.The larger the area of the white region, the more likely the node is

malignant. Both the estimated and the measured ratio of the white region within

the node are the most accurate predictors for malignant nodes in rectal cancer. The

estimated percentage can serve as a reliable and practical criterion for the

prediction of malignant nodes on USPIO-enhanced MR images(Lahaye etal.,2008).

The border and SI characteristics of lymph nodes on T2-weighted MR

images can be used for identification of malignant nodes in rectal cancer, however,

they are generally easier to evaluate in larger nodes (>5 mm in diameter). USPIO-

enhanced MR imaging and its characteristics are especially of additional benefit in

the evaluation of these small nodes (<5 mm in diameter) (Lahaye et al.,2008).

Benign conditions such as focal nodal fibrosis, granulomatous disease, or a

fatty hilum also can be depicted as a white region because of the lack of

macrophages, thus mimicking malignant nodes. These white regions, however, are

usually 30% or less of the total node area. Another way to differentiate between a

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white fatty hilum and a white tumoral region is to compare the T2*-weighted

images with the T1-weighted images: A fatty hilum is depicted as a white region

within the lymph node, whereas a tumor is not. In the same manner, the dark

region can hide small micrometastases. The clinical implication of

micrometastases,

however, is debatable. Although there is a small overlap in MR features of

benign

and malignant nodes, a general rule of thumb is that, when the white region is less

than 30% of the total node area, the nodes are most often benign (Lahaye etal.,2008). M staging

Hepatic metastases :

Colorectal hepatic metastases most commonly appear as lesions that are

moderately hyperintense on T2-w images and hypointense on T1-w images

(fig.78). ill-defined margin with slightly heterogeneous signal, or, occasionally, a

ring of surrounding high signal, or halo due to central necrosis or biliary or

vascular obstruction. In addition, they may also appear as target lesions with

central high signal and adjacent low signal corresponding to compressed hepatic

parenchyma(Saunders et al.,2002).

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Figure(59):(a,b,c) (a)Coronal T1 image of the liver in a patient under consideration for metastectomyshowing typical hypointense hepatic metastasis (arrow). (b)Axial T1-w image. (c)Axial T2-w image, themetastasis has a high signal centre (arrow) with an ill-defined margin (thin arrow) which is unusual in a

benign lesion(Saunders et al.,2002)

Gadolinium-enhanced imaging :

Gadolinium-based intravenous contrast agents can improve the sensitivity of

MRI in detecting metastases. Most metastases are hypovascular and receive their

blood supply from the hepatic artery in contrast to normal liver parenchyma which

receives 60-70% of its blood supply from the portal vein. During dynamically

enhanced scanning, metastases may be of increased signal during the arterial phase

and decreased signal in the portal phase. There may also be peripheral washout,

whereby the periphery of the metastasis is of lower signal than the centre and

adjacent liver. On delayed scanning, metastases may have increased

signal(Saunders et al.,2002).

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Figure(60)(a,b,c) (a)T1-w transverse scan with fat suppression. The hepatic metastasis at segment V ishypointense (arrow).

(b)Post-contrast transverse scan at arterial phase shows a hyperintense ring-like enhancement of the lesion(arrow), which is centrally hypovascular.

(c)Post-contrast transverse scan at portal venous phase illustrates washout of the peripheral enhancementof the metastasis (arrow), which remains hypovascular compared to the rest of the normally enhanced

liver parenchyma(Karantanas et al.,2007).

74


Advanced MR imaging techniques

Tumor imaging using diffusion-weighted imaging

On DW images, rectal cancer is depicted as hyperintense focal lesion (high

cellularity) with markedly enhanced contrast compared with T2-w image

(fig.80),few normal structures such as lymph nodes, small intestine, prostate,

seminal vesicles, testes and endometrium remain as hyperintense regions. Lower-

signal-intensity regions are seen in most organized normal tissues, cystic spaces,

and vessels(Figueiras et al.,2010).

Figure(61):(a,b) Rectal cancer in a 51-year old female patient. (a) Axial T2WI showed slight focalthickening of rectal wall (arrow), which were misinterpreted as no cancer present by the two readers.

(b)Axial DWI of the same plane demonstrated focal hyperintense area (arrow), which was found by thetwo readers. And endometrium remained as hyperintense regions (arrow head)( Rao et al.,2008).

High signal intensities on DW images are not always reliable indicators of

increased cellularity on their own. Occasionally, fluid, edema, or mucinous

materials remain of high signal intensity because of high proton density. This

observation is called T2-shine through, but this effect can be detected easily by

noting corresponding high signal on ADC maps(Figueiras et al.,2010

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Figure(62):(a,b,c) T3 rectal carcinoma in 64-year-old patient. (a) Sagittal fast spin-echo T2-weightedimage. (b) Sagittal diffusion-weighted image with high b value (b = 800 s/mm2) show rectal tumor as ahyperintense lesion. (c) Fusedsuperimposing sagittal T2-w MR image and color-coded map derived

from high-b-value diffusion-weighted image clearly delineates rectal carcinoma (arrows) (Figueiraset al.,2010).

76


Recent studies have already shown the potential value of DWI :

Detection of colorectal cancer, particularly when lesions are small and when

there is concurrent inflammatory disease with a high sensitivity (91%) and

specificity (100%)(Hoeffe et al.,2009).

Early prediction of treatment response because cell death and vascular

alterations typically occur before size changes. Increases in ADC values with

treatment reflect decreases in cellularity and thus provide indirect assessment of

chemotherapy induced cell death(Figueiras et al.,2010).

Assessing nodal metastases, however, this technique has not yet been shown

to be of value in characterizing lymph nodes in CRC patients. High-b-value DWI

is sensitive for detecting the location of lymph nodes, but its characterization value

is unproven in CRC with necrotic neoplastic nodes yielding false-negative results

and reactive hyperplastic nodes yielding false-positive results(Figueiras etal.,2010).

Patient selection; Responders to chemoradiation had a lower ADC at

presentation than nonresponders. Higher pretreatment ADC values in

nonresponders may reflect necrotic tumors that are more resistant to therapy

because of concomitant hypoxia which is the same for liver metastases(Figueiras

et al.,2010).

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I. Tumor imaging using dynamic contrast-enhanced MRI (DCE-MRI)(Perfusion MRI):

To date, there have been few data on the comparative performance of

perfusion CT and DCE-MRI. A study that compared the effectiveness of perfusion

CT with that of DCE-MRI for the assessment of solitary pulmonary nodules

concluded that there was no significant difference between the two techniques.

There are no data for colorectal cancer. In reality, the imaging technique chosen to

assess colorectal cancer vascularity is decided by local expertise, local availability,

perceived radiation burden, need for quantification, and site of disease(Goh etal.,2007).

II.Tumor imaging using MR colonography

MR colonography for polyp detection has seen relatively little progress and

only limited interest in recent years, there are a several MRI-related factors that

have contributed to its stunted growth. This includes the limited availability and

increased complexity of MRI, the continued use of a hydrocolon (water enema)

over gaseous distension of the colon due to technical issues related to the air-soft-

tissue interface. The hassle of performing an enema in the MRI suite is a major

impediment to wider dissemination(Pickhardt,2010).

Current protocols result in a relatively large number of series that must be

viewed, which can exacerbate reader fatigue. Although the sensitivity for detection

of large polyps and masses has approached that of CT colonography, gadolinium

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i.v. contrast is needed, which adds cost, time, complexity, and invasiveness over

CT colonography (Pickhardt,2010).

Another one of the major drawbacks of MR colonography is its inability to

detect accurately colorectal lesions smaller than 5 mm. The sensitivity for

detection of large polyps is about 75% with a high specificity(Hoeffel et al.,2009).

Re-staging of patients after chemoradiotherapy

The main purpose of MRI after chemoradiotherapy for locally advanced

rectal cancer is to evaluate treatment response and to determine the new tumor

extent(Torkzad et al.,2008).

Postchemoradiation MRI performed poorly on the prediction of T stage

(overall accuracy 54%). This was largely due to overstaging and the inability of

MRI to reliably distinguish between treatment fibrosis and viable tumor. However,

when considering results for the subgroup of ypT0-2tumors (confined to the rectal

wall)(ypT category:T category at posttreatment histopathologic evaluation), high

accuracy rates were found. . Downstaging of tumors to lesions confined to the

rectal wall with no longer involved lymph nodes can be followed with local

excision of the tumor(Low et al.,2008).

Postchemoradiation MRI has a moderate accuracy (sensitivity 100%,

specificity 32%-59%) for the prediction of tumor invasion of the mesorectal fascia

(MF) because of its limitations for differentiating diffuse “fibrotic” tissue with or

without small residual tumor foci. Specific morphologic tissue patterns identified

at MR imaging highly correspond with a tumor-free or

tumor-invaded MF(Vliegen et al.,2008).

79


MR imaging of nodal involvement is more difficult. The accuracy of MR

imaging for lymph node staging may improve with the recently introduced lymph

node-specific contrast agents(Dresen et al.,2009).

The use of DCE-MRI sequences remains questionable whether these

techniques would offer any help for the detection of small areas of tumor within

poorly vascularized fibrotic tissue(Vliegen et al.,2008).

T staging

The combination of morphologic and volumetric criteria can provide high

positive predictive value (83% to 92%) for the prediction of tumors confined to the

rectal wall (ypT0-2 Tumors) (Dresen et al.,2009).

Prediction of ypT0-2 tumors on basis of volume response to neoadjuvantchemoradiotherapy:

The maximum diameter is measured on one axial section in two directions

perpendicular to each other (length and width). The maximum height is measured

on one sagittal section. Tumor volume is obtained by multiplying tumor length,

width, and height. Volume reduction rates (as percentages) were defined as 100.

[(Vpre -V post) / Vpre ], where V pre is volume before and Vpostis volume after

chemoradiotherapy(Dresen et al.,2009).

Before chemoradiotherapy, if the initial tumor volume was ≤ 50cm3 and the

volume reduction rate after neoadjuvant chemoradiotherapy was ≥75%, then this

combination is predictive of a ypT0-2 tumor(Dresen et al.,2009).

80


All tumors with a volume reduction after chemoradiotherapy of less than

one-third of their original volume were ypT3-4 tumors(Dresen et al.,2009).

Figure(63):(a,b) Sagittal T2-w FSE MR images obtained after administration of chemoradiotherapy to3tumor with small volume (3.3x2.6x3.6cm=31cm ) show complete response at histopathologic

examination.

(a) Before chemoradiotherapy, tumor (T) is seen in rectum. (b) After chemoradiotherapy, tumorcompletely disappeared and normal rectal wall configuration was seen with dark outer layer (arrow) andhyperintense inner layer (arrowhead). At histopathologic evaluation, no residual tumor was found.

C=cervix,Co=coccygeal bone(Dresen et al.,2009).

Prediction of ypT0-2 tumors on basis of morphologic criteria:

Returning of the rectal wall to its normal configuration of a two layered

pattern on MR images is always associated with a complete histopathologic

disappearance of the tumor (ypT0 lesion) (Dresen et al.,2009).

Tumor surrounded by an intact hypointense bowel wall is highly predictive

of a tumor limited to the bowel wall. In many ypT0-2tumors, a normal

hypointense bowel wall is indeed visualized. However, when this bowel wall

appearance cannot be delineated, as for example when it has thickened owing to

radiation therapy, fibrosis is suggested. And these lesions are staged as ymrT3-4

tumors to prevent understaging as the interpretation of fibrosis with or without

residual tumor on MR images are difficult(Dresen et al.,2009)

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Mesorectal fascia invasion

Presence of a fat pad larger than 2mm between a residual (tumor) mass and

the MF is a definitive sign of absence of tumor invasion at postchemoradiation MR

imaging(Vliegen et al.,2008).

Presence of diffuse hypointense “fibrotic” infiltration of the MF at MR

imaging (seen in more than 50% of patients). In one of three quadrants, this

fibrotic tissue at MR imaging showed tumor infiltration at histologic examination.

Residual tumor within these fibrotic areas is often confined to small tumor nests. It

is therefore virtually impossible to differentiate these from completely sterilized

areas of fibrosis. “Fibrotic” areas should therefore be considered as potentially

invaded(Vliegen et al.,2008).

of diffuse iso-or hyperintense “tumor” infiltration of the MF at MR imaging

was associated with tumor invasion at histologic examination in 90%(Vliegen etal.,2008)

Figure(64): (a,b) Diffuse hypointense tissue infiltration at postchemoradiation MR imaging suggestive

of fibrosis can be associated with MF tumor invasion caused by residual tumor nests within fibrosis. V=

seminal vesicle, B=bladder, T=tumor.

82


(a,b) Transverse T2-w FSE MR images. (a) Prechemoradiation image shows diffuse isointense invasionof anterior MF (arrows) and left Seminal vesicle.

(b) Postchemoradiation image shows that this type of invasion has changed into diffuse hypointensetissue infiltration (arrows), suggesting diffuse fibrosis. Corresponding histologic slice shows a diffuse

fibrotic reaction that reaches the seminal vesicle and contains small residual tumor nests (Vliegen etal.,2008).

Other Changes After Chemoradiation Therapy

changes include rectal muscular wall fibrosis, rectal mucosal edema, new

presacral edema either behind or in front of the presacral fascia, peritoneal fibrosis,

and presacral fibrotic thickening(Allen et al.,2007).

The most common postchemoradiation therapy MRI change other than

staging characteristics is bone marrow fatty atrophy(Allen et al.,2007).

Mucinous tumors:

Tend to retain high signal intensity after chemoradiation therapy both in

primary tumors and in nodes and do not seem to shrink or change much

morphologically; these tumors did not seem to respond well to chemoradiation

therapy. This finding proved to be a source of error; in many of these cases,

histologic evaluation showed no active tumor but only inactive mucin lakes.

Mucinous differentiation after chemoradiation therapy can be found and does not

appear to be a poor prognostic factor in itself (Allen et al., 2007).

83

Summary and Conclusion


- Rectal cancer is the second most common cause of cancer in Females and the

third most common in Males it is the fourth most common cause of cancer death

after lung, stomach, and liver cancer.. It is more common in developed than

developing countries Risk factors include polyposis syndromes, inflammatory

bowel disease, dietary imbalance between fat, protein and fiber.

- MR imaging has become the most accurate technique in local staging of rectal

cancer, this is due to advances in terms of imaging equipment, coils, and sequences

that have progressively improved the technique, with a parallel increase in

accuracy. MRI can provide information regarding the site of tumor, the depth of

mural and extramural tumor spread, involvement of the circumferential resection

margin and indicate the extent of any sphincter involvement

- The main pitfalls that can be faced during an MRI is the difficulty in

differentiation between T1, T2 and T2, T3 stages (moderate accuracy for T-

staging), however this can have little impact on the management of patients.

- Identification of nodal disease continues to be a problem for radiologists. The

problem for morphologic imaging is their dependence on size criterion for

diagnosis. , the presence of an irregular contour and inhomogeneous signal were

found to be the most reliable MRI criteria for lymph node metastasis. USPIO-

enhanced MRI is a new promising approach to detect metastatic lymph nodes and

are especially of additional benefit in the evaluation of small nodes.

- Gd - enhanced MRI isthe highlysensitiveFor detection of hepatic metastases;

which represent the commonest site for distant metastatic spread. MRI can also be

84


used after chemoradiotherapy for locally advanced rectal cancer to evaluate

treatment response and to determine the new tumor extent.

- The recent introduction of powerful whole-body MRI systems enables imaging of

the whole body in a single session through repeated table movements. This

technique may be used for rectal cancer staging in the future allowing for local

staging and whole-body staging in a single session.

- Diffusion weighted imaging and perfusion MRI (DCE-MRI) have a growing rolein rectal cancer staging, while some other functional imaging modalities such andMR spectroscopy remain research-based, with limited clinical experience. DWIcan play a role in detection, staging and restaging of patients in terms of prognosis,therapy planning and monitoring

85

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93

المى Ϡ العرب خص

ان شتόانهخصAό ان δتثشسشغا ا IIIا��تمىحا �� م ϛ ان اسثاب δخش االث انخانجنذانشجال نذ ذذذذذذذذذذذذذذذذذذذذذذذذذذشغا ذ ذA ي δساتع ت نهفاج όثة انشئح ان سشغا όذ ϛذ انكثذ ا ات θخش ن�تمذيح � ذذل �� ا� �سا

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Aό ف Τتثش م� غ�ا ن� � تم�� δص الن انشاحم نتمى تصش غشمح م��م�أدق

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Πالست �ه �ϼόتح الش όد انسو غشأعه ذانتغIشانز ا��Aاع IIIانكIIIائ ي ��ز ��ز ��م ��ز نكا �� Cم ا .

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ϛ ان δΠايم جه ا� δى انت غشك ع Τح احذج الش نطأنح انتكشس όشك ي خطج ح

ي استخذايا ϼ تمثδانك ات حتصش تمى IIتت ��م��حج ��حم م θ ان سشغا δاس �� ا� ممى اءΤت

δΠان جه غحاء � δى تصش احذج ح

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تا Ϲنهتصش θت� A% أذ� �όس ا ف دسا ϑاθتϛة ات يشاحم تمى م�م��م�تمى إعادج �� م θ سشغا اسδان انشض تطس تمى حج ي ��حم��م�تمى ��م م

ال ϴنήدور ال δϴاطϨغϤن تق في ϴϴي ال اورام مϴقΘδϤم

لل توطئة Τرسالة ال درجة على όالشήϴΘδ اجϤصول ال ةϴصϴخθΘة

Ϙϣدϣةϣ نΘϔدالΒع ال رضا ايحδاح

ΎϜΑ وال الطب احةήΠلوريوسϴϠك ج - الطب ϣΎة طنط Ύعة

Τت IIIIإش افIIIIIήت

/ م. مدحت د ϤΤا رف تόدΎΘأس ورئ ϴذ ق δس ال الشعة ةϴصϴخθΘم

ϴϠك ج - الطب Ύنه ΑعةϣΎة

م . اسلم ϤΤد ال اذليθودϣ ال الشعة ةϴصϴخθΘدرسϴϠك ج - الطب Ύنه ΑعةϣΎة

όجام ب هــــــــاϨـــةϴكل الطـــــب ـــة

2015

Health & Medicine

mri of rectal cancer