Intractable epilepsy associated with angiographic obliteration of a medial temporal arteriovenous malformation following stereotactic radiosurgery

We present a case with recurrence of intractable complex partial epilepsy, despite angiographic obliteration of a cerebral arteriovenous malformation in the left medial temporal lobe following gamma knife radiosurgery. Preoperative memory function was normal, with no evidence of hippocampal atrophy by magnetic resonance imaging. Intraoperative electrocorticography demonstrated two independent foci of paroxysmal activity in the lateral and medial temporal lobes. As preoperative magnetic resonance imaging demonstrated subcortical hyperintensity, the lateral temporal lobe was resected. Histologically, there was evidence of subcortical myelin pallor, likely resulting from ischemic damage associated with hemodynamic changes following radiosurgery. As there was a decrease in the frequency of paroxysmal discharges in the hippocampus following arteriovenous malformation nidus removal, the hippocampus was preserved. Histological examination of the nidus revealed that some of the vessels had patent lumina, while ischemia affecting the neighboring hippocampus was considered to show improvement. A good seizure outcome was obtained. In summary, perioperative multimodal examinations, including intraoperative electrocorticography, revealed various epileptogenic mechanisms, probably related to myelin pallor in the lateral temporal lobe and focal ischemia secondary to patent AVM in the medial temporal lobe, of this patient.