P261 Middle latency auditory evoked potential (MLAEP) monitoring in midazolam induced anesthesia

Abstract

Brainstem cavernous malformations (BCM) have a high incidence of bleeding and rebleeding and carry a high rate of neurologic morbility. Locations in the tectal plate that represent a small percentage of BCMs have rarely been reported in the literature. The authors present a case of a patient with such localization who was successfully operated.A 24-year-old male known for having a tectal plate cavernoma with obstructive hydrocephalus, previously treated by shunting in another hospital, was admitted in our institute because of increasing headaches, gradual drowsiness, and the inability to stand up. Investigations revealed a compressive cavernoma lateralized on the left side of the tectal plate and a residual hydrocephalus in spite of the previous shunting. A new shunting procedure did not improve clinical conditions. Thus, an aggressive surgical resection was decided upon and was performed through an occipital-transtentorial approach with the aid of intraoperative brainstem and middle latency auditory evoked potentials (BAEPs/MLAEPs) monitoring. Total resection was achieved without significant deterioration except a hypovoltage of wave V after stimulation of the right ear, demonstrating a left collicular dysfunction. The patient was discharged on the 36th day after surgery. Seven months later, audiometry was normal, in spite of the persistence of the hypovoltage of the V wave after stimulation of the right ear, and functional status appraised using the Karnofsky score was at 100%. Professional activity could be resumed.Tectal plate cavernomas (TPC) represent a special entity of BCM. They are surgically accessible lesions on the dorsal aspect of the brainstem. Our preferred approach is the occipital-transtentorial approach. The use of intraoperative auditory evoked potentials monitoring make the surgical resection safer.