Auditory brain stem responses in cerebellopontine angle tumors

Area of Science:

• Neurology
• Neuroscience
• Otolaryngology

Background:

• Cerebellopontine angle tumors present diagnostic challenges.
• Auditory brain stem responses (ABSR) are crucial for evaluating auditory pathway integrity.

Purpose of the Study:

• To characterize ABSR patterns in patients with cerebellopontine angle tumors.
• To correlate ABSR findings with tumor characteristics and extent of involvement.
• To assess the utility of contralateral stimulation in evaluating brain stem displacement.

Main Methods:

• Analysis of ABSR in seven cases of cerebellopontine angle tumors (five acoustic neuromas, one cholesteatoma, one meningioma).
• Correlation of N1 response with auditory nerve involvement.
• Evaluation of brain stem displacement and cranial extension using contralateral stimuli.

Main Results:

• Tumors originating from the VIIIth nerve showed a distinct N1 complex, reduced subsequent responses, and prolonged brain stem conduction time (BSCT).
• Small tumors allowed normal central auditory pathway responses via contralateral stimulation.
• Medium to large tumors correlated with abnormal N2/N3 responses, indicating central auditory pathway involvement.

Conclusions:

• ABSR provides valuable insights into the functional status of the auditory nerve and brain stem in the presence of cerebellopontine angle tumors.
• The pattern of ABSR, particularly N1, N2, and N3 responses, aids in differentiating tumor types and assessing their impact on neural pathways.
• Contralateral stimulation offers additional information regarding the extent of the lesion and brain stem involvement.