RADIOLOGY TEACHING

CONFERENCE

John Athas, MD

Monica Tadros, MD

Columbia University, College of Physicians & Surgeons

Department of Otolaryngology- Head & Neck Surgery

September 27, 2007

CT SCAN IMAGING

Uses ionizing radiation to create cross-sectional images

Images separate planes based on relative density measured in Hounsfield units Bone is maximally bright [+1000 Hounsfield units],

Air is black [-1000 Hounsfield units]

Most useful to evaluate bone

KEY Point: Fat [-80 Hounsfield units] is darker than soft tissue or muscle allows any soft tissue bordered by a fat plane to be easily seen

allows displacement of a fat plane to signal pathology

Intravenous iodine contrast can be given to further stratify signal intensity among tissue planes helps many lesions become more conspicuous by identifying

vascularization of tissues

MAGNETIC RESONANCE

IMAGING

Uses a magnetic field to align protons and radiofrequency pulses to alter their precession. The protons subsequent relaxation time is used in generating an image.

Each tissue type emits a characteristic wave that corresponds to a sequence specific signal T1 sequence

T2 sequence

T1 with gadolinium sequence

FLAIR sequence

DWI sequence

Gradient-echo T2* sequence

T1 sequence

Conventionally uses traditional spin echo technique

for acquisition

Fat [blood, viscous protein] are very bright.

Muscle is gray

Fluid [CSF] is dark gray

T1 with gadolinium sequence

Gadolinium is the intravenous contrast agent

administered to identify vascularized tissues signaling

the presence of a mass

KEY Point: Gadolinium contrast sequence implies

T1 imaging

T2 sequence

Uses fast-spin echo technique for acquisition

Fluid [CSF] is very bright

Fallacy that fat is dark --fat is less bright on T2

Diffusion weighted imaging [DWI]

Surveys the movement of water within a pathologic lesion. Dark lesions are more likely fluid-filled or cystic lesions with

high diffusion.

Bright lesions on DWI are more likely solid lesions with restricted diffusion DWI is most advantageous in evaluating brain pathology and CPA

tumors

DWI is limited in determining head and neck and temporal bone pathology

Clinical Correlation: petrous apex cholesteatoma/epidermoid is a temporal bone lesion not well seen on DWI. Yet CPA epidermoid is well seen as bright on DWI therefore distinguishing it from other CPA tumors

FLuid Attenuated Inversion Recovery [FLAIR]

Surveys T2 bright lesions by suppressing free water

which is normally hyperintense on T2 images

Similar to the concept of fat suppression, FLAIR

sequence suppresses thin/mobile CSF fluid

[normally bright on T2] causing it to appear dark on

FLAIR.

Gradient-echo T2*sequence

Based on the rapid dephasing of stimulated

protons due to the presence of hemoglobin

Intracranial hemorrhage is best detected

results in hypointense (dark) lesions

This sequence has no significant application in the

head and neck.

1. On MRI, what do flow voids represent?

2. For what tumor type is this finding classic?

1- On MRI, what do flow voids represent?

2- For what tumor type is this finding classic?

High velocity blood flow causes stimulated

nuclei to leave the plane before relaxation

MRI signal appears black

This contrast – is best appreciated on

T2 sequences where fluid is normally bright

Key feature appreciated in Paraganglioma

With what sequences can fat

suppression be utilized? What is the

overall purpose of fat suppression?

With what sequences can fat suppression be utilized?

What is the overall purpose of fat suppression?

Fat suppression pulses are used on T1gad and T2 sequences to help subtract the brightness of fat that might be adjacent to a pathologic process

Clinical Correlations:

A small orbital meningioma may not be clearly delineated until the normal periorbital fat is suppressed on a T1gad sequence Prior to suppression the orbit appears all bright, after fat suppression

pulse of the T1 sequence, the periorbital fat is now dark and the meningioma can be identified as the sole bright area of pathology.

T1 gadolinium sequences surveying petrous temporal bone pathology may require fat suppression to identify enhancement that might otherwise by obscured by normal fatty marrow in the petrous bone

What imaging modality is ideal for initial

evaluation of the Temporal Bone?

What imaging modality is ideal for initial

evaluation of the Temporal Bone?

CT best visualizes presence of bone erosion in the bony external auditory canal, the ossicles, the mastoid, tegmen, semicircular canals, and facial nerve canal.

CT best demonstrates temporal bone and skull base fractures

Contrast enhanced CT helps delineate fluid of the inner ear with its surrounding otic capsule and demineralization of the otic capsule in cochlear otosclerosis

CT is useful in diagnosis of congenital anomalies of the cochlea, semicircular canals and vestibular aqueduct

What imaging modality is useful for

early detection of internal auditory

canal tumors and lesions of the

petrous apex?

What imaging modality is useful for early detection of internal

auditory canal tumors and lesions of the petrous apex?

MRI is more useful in detecting small IAC tumors.

CT depends on an expansile lesion in the bony canal

to permit detection and may miss smaller tumors

The variability of petrous apex lesions requires

MRI sequence characteristics to narrow the

differential diagnoses.

Which imaging modality is best for evaluation

of soft tissue tumors of the head and neck?

Both effective in evaluation of soft tissue tumors of the head and neck

Both can define tumor from adjacent fat planes equally well

Both can detect perineural spread by nerve enlargement or violation of adjacent fat planes, but MRI is superior within the skull base and cavernous sinus

CT or MRI can define extent of laryngeal tumors and preepiglottic or paraglottic invasion by distortion of fat planes.

MRI has an advantage in distinguishing tumor from muscle, making MRI more advantageous in evaluation of tumors of the tongue base which lack a fat plane interface

CT has an advantage in defining cortical bone erosion such as in tumors where there is question of mandibular invasion

CT can identify calcifications which may represent chondroid lesions

An 11-year-old boy with left neck mass

Based on the axial CT images, which category of disease is most

likely?

Neoplasm

Trauma

Infection/inflammation

Congenital

reloadme

A 28-year-old man with facial pain and double vision.

1. Select the relevant findings on review of the images (check all that apply)

Mastoiditis

Sphenoid dysplasia

Otitis media

Ossicular erosion

Enlargement of the facial canal

Temporal bone fracture

Enlargement of the foramen ovale.

2. What part of the temporal bone is involved? What disease process does this patient have?

15-year-old boy w/ history of chronic swelling around left eye.

Based on the images

what is the most likely

diagnosis?

A Esthesioneuroblastoma

B Allergic fungal sinusitis

C Juvenile nasal

angiofibroma

D Acute bacterial sinusitis

E Mucocele

Temporal Bone

Squamous

forms lateral wall of middle cranial fossa

Mastoid

Petrous

contains inner ear, internal auditory canal (IAC), petrous apex

Tympanic

forms most of bony external ear

Styloid process

Temporal

Bone:

Is it Normal?

15yo female presents with:

Hemotympanum

EAC laceration

Raccoon eyes

Battle’s sign-what artery?

Facial nerve weakness

What is highest on your differential?

Temporal Bone Fractures – Classify?

Temporal Bone Fracture: What type?

Temporal Bone Fracture: What type?

What deformity?

Acquired or Congenital?

What deformity?

What is your differential diagnosis?

Axial CT

T1 MRI- Noncontrast

How does this case differ?Axial CT

T1 MRI Noncontrast

30 yo male with painful vesiclular ear lesions

and facial paralysis. Diagnosis?

45 yo female w/ chronic sinusitis and

ballotable frontal collection

What complications might you be concerned about?

15 year-old boy with expansile mass

Speckled high attenuation represents what?

Noncontrast CT

See next slide-MRI

MRI

T1

T1

T1

w/

gad

T1

w/ gad

1- Describe the

findings.

2- What is your

differential

diagnosis?

30 year old female presents w/ pale fleshy

nasal mass

T1 Sagittal

T2

T2

See Next Slide

FLAIR DARK T2 BRIGHT

Differential

DIAGNOSIS

T1 T1 w/ Gad T2 FLAIR

Meningo-

encephalocele

Dark Rim

Enhancing/

central dark

Bright Dark

Mucocele Variable

[dept on

inspissated

sec]

Rim

Enhancing/

central dark

Iso/

Bright

Iso/

Bright

Polyp/Sinus

Inflammation

Dark Rim

Enhancing/

central dark

Bright Bright

Neoplasm Iso/

Dark

Homogen.

Enhance-

ment

Bright Bright

Describe the findings.

20 year-old male presents with hearing loss

Based on the MRI findings, what condition might this patient have?

What is the pattern of inheritance?