Intraoperative loss of auditory function relieved by microvascular decompression of the cochlear nerve

Background: Brainstem auditory evoked potentials (BAEP) are useful indicato rs of auditory function during posterior fossa surgery. Several potential m echanisms of injury may affect the cochlear nerve, and complete loss of BAE P is often associated with postoperative hearing loss, We report two cases of intraoperative auditory loss related to vascular compression upon the co chlear nerve. Methods: Intra-operative AEP were monitored in a consecutive series of over 300 microvascular decompressions (MVD) performed in a recent twelve-month period, In two patients undergoing treatment for trigeminal n euralgia, BAEP waveforms suddenly disappeared completely during closure of the dura, Results: The cerebello-pontine angle was immediately re-explored and there was no evidence of hemorrhage or cerebellar swelling. The cochlea r nerve and brainstem were inspected, and prominent vascular compression wa s identified in both patients. A cochlear nerve MVD resulted in immediate r estoration of BAEP, and both patients recovered without hearing loss, Concl usion: These cases illustrate that vascular compression upon the cochlear n erve may disrupt function, and is reversible with MVD. Awareness of this ev ent and recognition of BAEP changes alert the neurosurgeon to a potential r eversible cause of hearing loss during posterior fossa surgery.