Treatment of intractable arterial hemorrhage during stereotactic brain biopsy with thrombin. Report of three patients. Of 165 consecutive patients undergoing computerized tomography- or magnetic resonance imaging-guided stereotactic brain biopsies at the Cleveland Clinic between June, 1987, and November, 1989, four patients (2.4%) developed arterial hemorrhage refractory to conventional efforts to secure hemostasis. Craniotomy was performed in one of these patients to control the hemorrhage; in the other three, 0.5 to 2 cc of thrombin (5000 U/cc) was slowly injected via the biopsy cannula, resulting in immediate control of bleeding in all three cases. Postoperatively, the first two patients treated with 1 to 2 cc of thrombin were slow to awaken; one had evidence of vasospasm by transcranial Doppler ultrasound studies and multiple infarcts on cranial computerized tomography, while the other had a moderate-sized frontal hematoma with intracranial hypertension. After prolonged recovery periods, only mild neurological deficits persisted in both patients. The third patient, treated with 0.5 cc of thrombin, had an uneventful postoperative course. Thrombin is highly effective for stopping intractable arterial hemorrhage during stereotactic brain biopsy; however, it is a vasospastic agent and may have been responsible for the cerebral infarctions in one patient. Therefore, thrombin should be used only as a last resort, short of craniotomy, to control intractable arterial hemorrhage during stereotactic brain biopsy. 