What is the diagnostic work-up for hearing loss caused by a vascular loop over the 8th (eighth) cranial nerve?

Diagnostic Work-up for Hearing Loss Caused by Vascular Loop over the 8th Cranial Nerve

MRI of the head and internal auditory canal without and with IV contrast is the gold standard for diagnosing vascular compression of the vestibulocochlear nerve. 1

Initial Clinical Assessment

• Perform thorough otologic examination to rule out other causes of hearing loss 1
• Assess for unilateral or asymmetric sensorineural hearing loss, which is the most common audiometric finding in vascular compression syndrome 2
• Document presence of tinnitus (often unilateral), which occurs in approximately 89% of patients with vascular compression syndrome 3
• Evaluate for vestibular symptoms, which are present in about 61% of cases 3

Audiometric Evaluation

• Conduct pure tone audiometry to characterize the type and severity of hearing loss 3
• Perform speech discrimination testing (patients with vascular compression typically have excellent speech discrimination compared to those with acoustic neuromas) 4
• Complete distortion product otoacoustic emissions (DPOAE) testing to assess cochlear function 3
• Conduct auditory brainstem response (ABR) testing, looking specifically for:
  • Prolongation of I-III interval (Moller's criteria) 3
  • Asymmetry between ears in I-III, III-V, and I-V intervals 3

Vestibular Testing

• Perform electronystagmography (ENG) to assess for:
  • Spontaneous nystagmus (present in most patients with vascular compression) 4
  • Caloric response abnormalities (weakness or absence in approximately 46% of cases) 3

Imaging Studies

MRI Protocol

• MRI of the head and internal auditory canal without and with IV contrast is the primary imaging modality 1
• Include the following sequences:
  • Standard T1- and T2-weighted sequences 1
  • Diffusion-weighted imaging (DWI) 1
  • Fluid-attenuated inversion recovery (FLAIR) sequences 1
  • Axial submillimetric heavily T2-weighted sequences (FIESTA, CISS, or DRIVE) to evaluate the vestibulocochlear nerve and its branches 1
  • Post-gadolinium T1-weighted sequences 1

MR Angiography

• MRA of the head without and with IV contrast should be performed to better visualize vascular structures 1
• This helps to detect and characterize the relationship between the anterior inferior cerebellar artery (AICA) loop and the eighth cranial nerve 1

Important Diagnostic Considerations

• Vascular loops in contact with cranial nerve VIII are found in approximately 25% of symptomatic ears but also in 21.4% of asymptomatic ears, making correlation with clinical findings essential 5
• Patients with vascular compression syndrome typically present with:
  • Unilateral sensorineural hearing loss (often cochlear type) 6
  • Excellent speech discrimination (unlike acoustic neuromas) 6, 4
  • Spontaneous nystagmus on vestibular testing 6
  • Normal caloric test results in approximately 50-67% of cases 6, 3

Differential Diagnosis

• Acoustic neuroma (vestibular schwannoma) 1
• Ménière's disease 1
• Idiopathic sudden sensorineural hearing loss 1
• Multiple sclerosis 1
• Other cerebellopontine angle masses (meningioma, endolymphatic sac tumor) 1

Diagnostic Pitfalls to Avoid

• Do not assume that radiologic demonstration of contact between a vascular loop and the eighth cranial nerve is pathologic, as this can be a normal anatomic finding 5
• Always correlate imaging findings with clinical and audiometric data 5
• Remember that vascular loops are prevalent in asymptomatic individuals and should not obviate a search for another explanation for hearing loss 1
• Be aware that the significance of vascular contact or impingement of the cisternal eighth cranial nerve remains debated in the literature 1