A patient with acoustic neuroma undergoes surgery via the retrosigmoid approach. Intraoperatively, the ABR waveform is being monitored. Sudden loss of Wave V amplitude suggests injury to which structure?

• A Inferior colliculus (midbrain); compressive injury from retraction leads to prolonged Wave I-V interval then loss of Wave V
• B Cochlear nerve (cochlear end-organ) being stretched; Wave I is preserved but Wave V is lost indicating post-spiral ganglion injury
• C Facial nerve monitor showing EMG activity indicating motor nerve involvement
• D Cochlear blood supply compromise (labyrinthine artery compression) with loss of all ABR waves from Wave I onward ✓

Explanation

During retrosigmoid approach for acoustic neuroma, sudden complete ABR wave loss (beginning with Wave I) indicates cochlear blood supply compromise — labyrinthine artery occlusion from retraction or coagulation. This is the most ominous intraoperative finding and often results in permanent profound SNHL. Isolated Wave V loss with preserved Wave I suggests brainstem/auditory pathway compromise distal to the cochlea. Gradual Wave V latency increase (I-V interpeak prolongation) suggests cochlear nerve stretch and may be reversible if addressed promptly.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.