RADIOLOGY TEACHING CONFERENCE

Transcription

1 RADIOLOGY TEACHING CONFERENCE John Athas, MD Monica Tadros, MD Columbia University, College of Physicians & Surgeons Department of Otolaryngology- Head & Neck Surgery September 27, 2007

2 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

3 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

4 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

5 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

6 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

7 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

8 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.

9 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.

10 1. On MRI, what do flow voids represent? 2. For what tumor type is this finding classic?

11 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

12 With what sequences can fat suppression be utilized? What is the overall purpose of fat suppression?

13 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

14 What imaging modality is ideal for initial evaluation of the Temporal Bone?

15 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

16 What imaging modality is useful for early detection of internal auditory canal tumors and lesions of the petrous apex?

17 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.

18 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

19 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

20 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?

21 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

22 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

23 Temporal Bone: Is it Normal?

24 15yo female presents with: Hemotympanum EAC laceration Raccoon eyes Battle s sign-what artery? Facial nerve weakness What is highest on your differential?

25 Temporal Bone Fractures Classify?

26 Temporal Bone Fracture: What type?

27 Temporal Bone Fracture: What type?

28 What deformity? Acquired or Congenital?

29 What deformity?

30 What is your differential diagnosis? Axial CT T1 MRI- Noncontrast

31 How does this case differ? Axial CT T1 MRI Noncontrast

32 30 yo male with painful vesiclular ear lesions and facial paralysis. Diagnosis?

33 45 yo female w/ chronic sinusitis and ballotable frontal collection What complications might you be concerned about?

34 15 year-old boy with expansile mass Noncontrast CT Speckled high attenuation represents what? See next slide-mri

35 MRI 1- Describe the findings. 2- What is your differential diagnosis? T1 T1 T1 w/ gad T1 w/ gad

36 30 year old female presents w/ pale fleshy nasal mass T1 Sagittal T2 T2 See Next Slide

37 FLAIR DARK T2 BRIGHT

38 Differential DIAGNOSIS Meningoencephalocele Mucocele Polyp/Sinus Inflammation Neoplasm T1 T1 w/ Gad T2 FLAIR Dark Variable [dept on inspissated sec] Dark Iso/ Dark Rim Enhancing/ central dark Rim Enhancing/ central dark Rim Enhancing/ central dark Homogen. Enhancement Bright Iso/ Bright Bright Bright Dark Iso/ Bright Bright Bright

39 Describe the findings.

40 Based on the MRI findings, what condition might this patient have? What is the pattern of inheritance? 20 year-old male presents with hearing loss