When should you order a Magnetic Resonance Imaging (MRI) of the auditory canal?

MRI of the Auditory Canal: Indications and Protocol

MRI of the auditory canal should be ordered for patients with asymmetric sensorineural hearing loss, sudden sensorineural hearing loss, or symptoms suggesting retrocochlear pathology to rule out vestibular schwannomas and other potentially serious conditions. 1

Primary Indications for MRI of the Auditory Canal

• Sudden sensorineural hearing loss (SSNHL)

  • MRI should be ordered to screen for vestibular schwannomas in patients with SSNHL 1
  • The prevalence of cerebellopontine angle tumors in SSNHL patients ranges from 2.7% to 10.2% 1

• Asymmetric sensorineural hearing loss

  • Particularly when asymmetry is in the mid to high frequency range (3000 Hz) 1
  • When speech recognition scores are worse than expected for pure tone averages 1

• Suspected retrocochlear pathology

  • Symptoms suggesting central causes of vertigo
  • Unilateral tinnitus with hearing loss
  • Facial paresthesia or pain with hearing loss 2

MRI Protocol Specifications

• Dedicated internal auditory canal (IAC) protocol should be used 1, 3

  • High-resolution 3D T2-weighted sequences (CISS, FIESTA, SPACE, or DRIVE)
  • Thin sections across the IAC and inner ear (submillimeter assessment)
  • Evaluation of brainstem and thalami included in protocol 3

• Contrast considerations

  • IV contrast can facilitate visualization of inflammatory changes and neoplasms 1
  • However, non-contrast high-resolution T2-weighted imaging alone may be sufficient for screening, with 84-100% sensitivity for detecting intralabyrinthine schwannomas 4
  • Consider contrast for better characterization if abnormalities are detected on initial screening 3

When CT May Be Preferred Over MRI

• Bony abnormalities

  • Superior semicircular canal dehiscence
  • Temporal bone fractures
  • Otospongiosis
  • Labyrinthine ossification 1, 3

• Pre-surgical planning for cochlear implantation 1

Clinical Pearls and Pitfalls

• Pearl: MRI can detect masses as small as 2mm in the IAC, making it superior to other screening methods 5

• Pitfall: Relying on auditory brainstem response (ABR) testing alone may miss small lesions, particularly in patients with severe hearing loss 1, 5

• Pearl: Recovery of hearing does not eliminate the possibility of a tumor - MRI should still be considered in patients with resolved SSNHL 2

• Pitfall: Using standard head CT or MRI protocols instead of dedicated IAC protocols may lack the resolution needed to detect small abnormalities 3

• Pearl: Non-contrast high-resolution T2WI may be sufficient for screening, potentially reducing costs, time, and adverse events associated with gadolinium administration 4, 6

• Pitfall: Delaying MRI in patients with sudden hearing loss may lead to delayed diagnosis of acoustic neuromas, as sudden hearing loss can be an unusual initial symptom of these tumors 2

By following these evidence-based guidelines for ordering MRI of the auditory canal, clinicians can ensure appropriate imaging for patients with hearing and balance disorders while minimizing unnecessary testing and optimizing diagnostic yield.