The role of monopolar stimulation during computed-tomography-guided stereotactic biopsies.

44 patients underwent intraoperative stimulation with a monopolar electrode prior to computed tomography (CT)-guided stereotactic biopsy. Stimulation at 2-100 Hz resulted in functional responses in 6/21 patients with subcortical or callosal lesions, 4/6 with basal ganglion lesions, 8/10 with thalamic and 4/4 with brainstem lesions. In all but 2 patients with mesencephalic lesions, where limited biopsy sites were available, an alternative biopsy site was used if a functional response was obtained. No morbidity was seen among these patients, although postbiopsy CT scans demonstrated small 3- to 7-mm hematomas in 5/11 patients. Retrospective review of 79 patients who underwent biopsies without stimulation demonstrated hematomas in 6/10 patients and a 3.3% transient surgical morbidity. These data indicate that postbiopsy hematomas are a relatively common occurrence, that intraoperative electrical stimulation within abnormal lesions can identify functional potential, and that avoidance of biopsies within these functional areas may be associated with reduced morbidity.