What is the recommended CT (Computed Tomography) imaging protocol for diagnosing labyrinthitis?

CT Imaging Protocol for Labyrinthitis

For diagnosing labyrinthitis, MRI head and internal auditory canal without and with IV contrast is the preferred imaging modality over CT, as it better demonstrates enhancement of the vestibule or semicircular canals and provides superior soft tissue resolution. 1

Imaging Modality Selection

Primary Recommendation: MRI

• MRI head and internal auditory canal without and with IV contrast is the optimal imaging choice for labyrinthitis because:
  • It allows visualization of enhancement of vestibule or semicircular canals in patients with labyrinthitis 1
  • Provides superior differentiation between normal and involved soft tissues 1
  • Shows juxta-osseous contrast enhancement better than CT 1
  • Demonstrates superior detection of labyrinth involvement 1

When CT is Necessary

If CT must be used (due to MRI contraindications, availability issues, or need for bony detail):

• CT temporal bone without IV contrast should be performed with:
  • High-resolution technique
  • Submillimeter slice thickness (≤1.5 mm)
  • Bone window settings 2
  • Consider adding IV contrast to detect enhancement of vestibule or semicircular canals 1

Clinical Correlation

The imaging findings should be correlated with clinical presentation:

• Acute onset of vertigo, hearing loss, and nausea/vomiting
• Possible tinnitus and aural fullness
• History of preceding infection (especially otitis media)

Special Considerations

1. Labyrinthitis Ossificans:

   • Late complication of labyrinthitis
   • CT is actually better than MRI for detecting ossification of the membranous labyrinth 3
   • Important to diagnose before cochlear implantation as ossification can hinder electrode placement 3

2. Complications to Assess:

   • Evaluate for concomitant complications, which are common with suppurative labyrinthitis:
     • Labyrinthine fistula
     • Meningitis
     • Facial paralysis
     • Mastoiditis
     • Intracranial abscess 4

3. Timing of Imaging:

   • Early imaging is crucial for optimal sensitivity
   • Ideally performed before treatment is initiated 5

Pitfalls and Caveats

• CT has limited sensitivity for early labyrinthitis changes compared to MRI
• MRI sensitivity for subclinical labyrinthitis may still be suboptimal if performed late 5
• Contrast enhancement on MRI is critical for diagnosis of active labyrinthitis 6
• Definitive diagnosis of labyrinthitis is often made retrospectively based on clinical improvement and imaging findings 6

Diagnostic Algorithm

1. First-line: MRI head and internal auditory canal without and with IV contrast
2. If MRI contraindicated: High-resolution CT temporal bone without IV contrast
3. If bony details needed: Consider both modalities for complete evaluation
4. If complications suspected: Add brain sequences to evaluate for intracranial extension

Remember that while imaging is valuable, the diagnosis of labyrinthitis is often based on a combination of clinical presentation, audiometric testing, and imaging findings.