Modality
CT & high-resolution CT
When the question is bony — a dehiscence, an erosion, a fracture line, a pneumolabyrinth — CT, and specifically high-resolution temporal bone CT, is the modality of choice. Its spatial resolution exposes osseous detail no MRI sequence can match.
When CT is the right answer
CT shines on bone. In vertigo, the bony pathologies that matter are superior semicircular canal dehiscence, otosclerosis, temporal bone fracture, ossifying labyrinthitis after meningitis, cholesteatoma erosion into the labyrinth, and pneumolabyrinth after barotrauma. MRI cannot resolve any of these reliably.
High-resolution CT (HRCT) of the temporal bone is the workhorse — thin-section (≤0.6 mm), bone-window acquisition, reconstructed in axial, coronal, and the two essential oblique planes: Pöschland Stenvers. Both are reconstructed from the same source acquisition; Pöschl profiles the superior canal end-on, Stenvers along its long axis.
For SSCD, the Pöschl plane is essentially compulsory. Axial-only review consistently over-diagnoses dehiscence because volume averaging over the curved bony roof can look like a defect.1Confidence demands the canal profiled perpendicular to its long axis, with the defect demonstrable on at least two consecutive slices. Surgical plugging in truly dehiscent symptomatic patients reduces dizziness handicap meaningfully.2
Pneumolabyrinth — air within the cochlea or vestibule — is pathognomonic of a perilymph fistula. After head or barotrauma, its presence is the imaging finding that confirms the clinical suspicion when direct visualisation of the fistula is impossible.
Order HRCT with explicit instructions for thin-slice acquisition and Pöschl plus Stenvers reformatting when SSCD is on the differential. For trauma, ask for review of the otic capsule (transverse fractures cross it, longitudinal fractures generally do not), ossicular chain disruption, facial canal involvement, and pneumolabyrinth.
Limitations: ionising radiation matters in paediatric patients and for serial imaging. CT is insensitive to brainstem or cerebellar pathology, particularly early ischaemia, which means a normal CT in an AVS patient with vascular risk does not exclude posterior-fossa stroke. CT angiography (covered next) extends CT into the vascular question.
Reconstruction planes — orient before you call
Three orthogonal planes (axial, coronal, sagittal) plus two oblique reconstructions (Pöschl, Stenvers) make up the workable temporal-bone repertoire. Each plane answers a different question; the Pöschl plane in particular is what makes confident SSCD calls possible.
The Pöschl plane — why it matters
Toggle between axial and Pöschl reconstructions across three cases: an intact roof, a near-dehiscence, and frank dehiscence. The axial view looks similar across the three; the Pöschl plane separates them.
Read
Definite bony gap over the canal apex on Pöschl — the diagnostic finding.
Pitfall
Look for the dehiscence on at least two consecutive Pöschl slices.
Other CT indications in the vertigo work-up
- Otosclerosis — fenestral type (lucent zones anterior to the oval window) and retrofenestral type with cochlear involvement.
- Labyrinthitis ossificans — progressive obliteration of cochlea and vestibule after bacterial labyrinthitis or meningitis; early detection alters cochlear-implant timing.
- Cholesteatoma with labyrinthine involvement — CT defines bony erosion; MRI-DWI characterises the soft-tissue mass.
- Temporal bone fractures — otic-capsule-violating versus sparing, with planning consequences for facial-nerve repair and ossiculoplasty.
- Pre-operative bony anatomy — mastoid pneumatisation, sigmoid sinus and jugular bulb dominance, facial canal course.