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Downloaded from sar2013.conferencespot.orgDownloaded from sar2013.conferencespot.orgDownloaded from sar2013.conferencespot.orgDownloaded from sar2013.conferencespot.orgDownloaded from sar2013.conferencespot.orgDownloaded from sar2013.conferencespot.org
12/28/2012
Best in Practice Protocols: Rectal MRI
Mukesh Harisinghani, MD
Overview
• Pertinent anatomy and staging information
• MR Imaging– Protocol– Imaging pointers for surgical resection and
staging
– What to include in the report
Evaluation of Rectal Cancer Colo-Rectal Cancer
• Rectal cancer as a entity is inseparable from colorectal group
• Third most common cancer worldwide
• 2010– New cases: 39,670 (rectal cancers only)– Deaths (colon and rectal cancers
combined): 51,370
MRI Local Staging
EndoSonogr
(ERUS) Stagi
Rectal Ultra aphy
Local ng
PET CT Metastatic Work
up
Why MRI
• Excellent depiction of anatomy• MRI superior to ERUS in determining
the depth of transmural invasion (T stage) and local extension
• MRI comparable to ERUS for detecting lymph node metastases (N stage)
World J Gastroenterol 2008; 14(22): 3504
Rectal Anatomy
Upper Rectal Tumor: 12 -16 cm
Middle Rectal Tumor: 6-12 cm
Lower Rectal Tumor: < 6 cm
16 cm
1
2
3
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T2 W
Mucosa and Submucosa
Muscularis PropriaT2 W
MR Rectal Wall
HyHpyopinetreinseensDearRkinRging
T2 W
Pelvic Floor
Terms We Need to be Familiar With
• Mesorectal fascia
• Total Mesorectal Excision (TME)• Circumferential Resection Margin
(CRM)Mesorectal
Fascia
Total Mesorectal Excision(TME)
Circumferential Resection Margin (CRM)
• The shortest distance from the tumor or lymph nodes to the mesorectal fat is called the circumferential resection margin (CRM).
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MRI Rectal Protocol
Torso Phased ArrayMulti Channel Coil
> T2 –SAG
> Hi Res Oblique T2:Axial and Coronal
> Wide FOV Ax T2
Diffusion Weighted Images
Multiphasic Gd-Enhanced Series
1.5T or 3T
MR Pointers: Oblique Plane
MR Pointers
• Optimal TE on T– ~ 60 msec
2w
MRI Pointers
• Motion Correction– BLADE / PROPELLER
MRI Pointers: Time Saver
T2 SPACE/CUBE
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Role of MR Imaging
• Stratify patients into the following categories to guide presurgical therapy and surgical resection
– Early
– Local spread
– Distant Spread
What Matters and We Should Evaluate on MRI
• T stage
• CRM status
• Nodal stage
• Position of tumor
• T stage
• CRM status
• N stage
• Position of tumor
T1
T2
T3
Luminal Length Not as Important as Lateral Spread
T3T2
T4
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Beware of Desmoplastic Reaction
T3 T2
• T stage
• CRM status
• N stage
• Position of tumor
• When is CRM threatened– Primary tumor, tumor deposit or positive
lymph node in close proximity to mesorectal fascia
– <1 mm of CRM
– Bad prognosis; high recurrence rate
– Negative when distance > 6 mm
• T stage
• CRM status
• N stage
• Position of tumor
Good T3Bad T3Bad T3Bad T3
• T stage
• CRM status
• N stage
• Position of tumor
Most positive nodes are 5 – 7 mm in size
• T stage
• CRM status
• N stage
• Position of tumor
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• T stage
• CRM status
• N stage
• Position of tumor
Irregular Margins Heterogenous Signal
MR Accuracy
• T Staging : 65-91 %
• N Staging : 43-85 %
• CRM : 95 %
MRI is more accurate in predicting free resection margin than T stage !!!
Beets-Tan RG et al. Lancet 2001 Brown G et al. BJS 2003 & RSNA 2004 Nagtegaal I et al. Am J Surg Path 2002
Report• Location of the tumor in low, mid or high
rectum
• Length of the tumor for surgicalplanning
• Circumferential or not;
• T-stage; T3• Circumferential resection margin in mm
on anterior, posterior and lateral side.
• N-stage
Conclusion
• MRI useful for T staging and CRMstatus determination
• Used to stratifying patients prior totherapy
• Attention to proper technique is critical
• Role of DWI still emerging
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