In an adult with conductive hearing loss and a normal type A tympanogram, should I order a high‑resolution non‑contrast CT of the temporal bone or a CTA of the head?

Order High-Resolution Non-Contrast CT of the Temporal Bone

In an adult with conductive hearing loss and a normal type A tympanogram, you should order a high-resolution non-contrast CT of the temporal bone, not a CTA of the head. 1

Rationale for CT Temporal Bone

Temporal bone CT is the first-line imaging modality for conductive hearing loss without a middle ear mass. 1 This recommendation is based on the following:

Diagnostic Capabilities

• CT provides excellent visualization of the ossicular chain, external auditory canal, and bony labyrinth structures that are the primary causes of conductive hearing loss with a normal tympanic membrane. 1

• Key pathologies identified include:

  • Otosclerosis (otospongiosis) - the most common cause, found in 92.2% of surgical cases 2
  • Ossicular erosion or fusion 1
  • Round window occlusion 1
  • Superior semicircular canal dehiscence (SSCD) - a critical diagnosis that can mimic otosclerosis 1, 3, 4

Technical Considerations

• Contrast is not beneficial because the dense temporal bone obscures soft tissue enhancement, and the pathology involves bony structures best seen on bone windows. 1

• High spatial resolution is essential for visualizing small structures like the ossicles and detecting subtle bony changes. 1, 5

• Special reconstructions along the Pöschl plane and perpendicular to the Stenver plane should be performed if SSCD is suspected, as this can cause conductive hearing loss through a "third window" mechanism. 1

Why NOT CTA Head

There is no evidence to support use of CTA in patients with conductive hearing loss. 1

• CTA evaluates vascular structures, which are not relevant to the bony and mechanical causes of conductive hearing loss. 1

• The only exception is when there is high clinical suspicion of middle ear paraganglioma with a visible middle ear mass on otoscopy - but your patient has a normal tympanogram, making this unlikely. 1

Critical Pitfall: Don't Miss SSCD

Superior semicircular canal dehiscence is a frequently overlooked cause of conductive hearing loss with normal middle ear examination. 3, 4

• SSCD creates apparent conductive hearing loss through dissipation of acoustic energy via the bony dehiscence, producing air-bone gaps averaging 24 dB. 4

• Patients may undergo unnecessary stapedectomy if SSCD is not identified preoperatively. 4

• The CT sensitivity for otosclerosis is 91.3%, but 8.7% of early fenestral otosclerosis cases may be "infra-radiological" and appear normal on CT. 2

Clinical Context

Your patient's normal type A tympanogram indicates normal middle ear pressure and tympanic membrane mobility, which excludes middle ear effusion or tympanic membrane perforation. 1 This makes structural bony abnormalities the most likely etiology, reinforcing the need for high-resolution temporal bone CT rather than vascular imaging.