Temporal Bone CT Recognition Pattern

Systematic approach to interpreting temporal bone CT scans with key anatomical landmarks and pathological patterns

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1. Basic Principles

A. Acquisition Parameters

• Slice thickness:
  - 0.5-0.625mm ideal
  - Allows multi-planar reconstruction
• Windows:
  - Bone window (WW 4000, WL 600)
  - Soft tissue window for masses

B. Standard Planes

• Axial:
  - Parallel to infraorbitomeatal line
  - Best for ossicles, facial nerve canal
• Coronal:
  - Perpendicular to hard palate
  - Best for tegmen, oval/round windows
• Stenver's:
  - 45° oblique to petrous ridge
  - Best for cochlea, vestibular aqueduct
• Pöschl:
  - Perpendicular to Stenver's
  - Best for IAC, semicircular canals

2. ABCDEF Systematic Approach

Step	Assessment	Key Elements
A	Anatomy	Overall structure, symmetry
B	Bony structures	Tegmen, mastoid air cells, cortex
C	Cochlea/Vestibule	Mondini, semicircular canals
D	Drainage	Mastoid air cells, Eustachian tube
E	External/Middle ear	EAC, ossicles, Prussak's space
F	Facial nerve	Fallopian canal, dehiscence
G	Great vessels	ICA, jugular bulb, aberrant vessels

3. Key Anatomical Structures

A. External Ear

• External Auditory Canal (EAC):
  - Normal diameter 6-8mm
  - Look for exostoses, cholesteatoma

B. Middle Ear

Structure	Location	Key Features
Malleus	Attached to TM	Head in epitympanum
Incus	Between malleus/stapes	Short process in fossa incudis
Stapes	Oval window	Crura often visible
Prussak's Space	Lateral to ossicles	Common cholesteatoma site

C. Inner Ear

• Cochlea:
  - 2.5 turns
  - Modiolus central axis
  - Look for Mondini malformation
• Vestibule/SCCs:
  - Superior/lateral/posterior canals
  - Normal width <1.5mm
  - Look for dehiscence
• IAC:
  - Normal diameter 4-8mm
  - Fundal crest divides nerves

4. Pathology Patterns

A. Inflammatory

Condition	Findings	Key Features
Acute Otomastoiditis	Air cell opacification	± Bone destruction (coalescence)
Cholesteatoma	Soft tissue mass	Prussak's space, scutum erosion
Chronic Otitis Media	Mucosal thickening	Ossicular erosion, tympanosclerosis

B. Trauma

• Longitudinal fracture:
  - Parallel to petrous ridge
  - Through EAC, middle ear
  - Ossicular disruption common
• Transverse fracture:
  - Perpendicular to petrous ridge
  - Through cochlea, IAC
  - Facial nerve injury common
• Ossicular disruption:
  - Incudostapedial joint most common
  - Malleus fracture rare

C. Congenital

• Mondini malformation:
  - Incomplete cochlear partition
  - 1.5 turns instead of 2.5
• Large Vestibular Aqueduct:
  - Midpoint width >1.5mm
  - Common cause pediatric SNHL
• SCC Dehiscence:
  - Superior canal most common
  - Causes Tullio phenomenon

5. Vascular Variants

Variant	Location	Significance
High Jugular Bulb	Above inferior tympanic ring	Risk of injury during surgery
Dehiscent Jugular	Middle ear cavity	Pulsatile tinnitus
Aberrant ICA	Posterolateral to cochlea	Mimics glomus tumor
Persistent Stapedial Artery	Through stapes crura	Absent foramen spinosum

6. Temporal Bone CT Reporting Template

1. Technique:
   - Slice thickness, planes
   - Contrast (if used)
2. External ear:
   - EAC patency
   - Bony abnormalities
3. Middle ear:
   - Ossicular integrity
   - Mastoid aeration
   - Soft tissue abnormalities
4. Inner ear:
   - Cochlear turns
   - SCC morphology
   - IAC dimensions
5. Facial nerve:
   - Canal integrity
   - Dehiscence
6. Vascular structures:
   - Jugular bulb position
   - ICA course

Always correlate with clinical history and otoscopic findings. Review in both bone and soft tissue windows when masses are suspected. For cholesteatoma, carefully evaluate for bony erosion. In trauma, describe fracture orientation and relationship to critical structures. For congenital hearing loss, assess cochlear morphology and vestibular aqueduct size. Note any vascular variants that may impact surgical planning.

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