Loss of SSEP during sitting craniotomy

A 54-year-old woman with a past medical history of asthma and depression presented with right side hearing loss and ataxia. She was scheduled for a sitting craniotomy for cerebellopontine angle tumor resection. Somatosensory evoked potential, brainstem auditory evoked response, and facial nerve EMG were monitored intraoperatively. Approximately 30 minutes into the case, there was an episode of air embolism, which resolved after the source was identified and treated. Near the conclusion of the case, there was an abrupt loss of the right cortical somatosensory evoked potential signal, which never returned to baseline. A postoperative CT scan showed a substantial amount of subarachnoid air and intraventricular air in the frontal and temporal regions. The patient awakened in the ICU with no new neurologic deficit besides preoperative hearing loss on the right side. Despite the high specificity of somatosensory evoked potential change associated with postoperative neurodeficit when the change never returns to the baseline, there was no postoperative neurologic deficit in this patient. This case indicates the false-positive somatosensory evoked potentials caused by pneumocephalus in the sitting position.