Monitoring of the lateral spread response in the endovascular treatment of a hemifacial spasm caused by an unruptured vertebral artery aneurysm. Case report.

The lateral spread response (LSR) is used in the electrophysiological diagnosis of a hemifacial spasm or for monitoring during microvascular decompression. The authors used LSRs for intraoperative monitoring during endovascular surgery in a rare case of vertebral artery (VA) aneurysm that caused intractable hemifacial spasm. A 49-year-old woman presented with a right hemifacial spasm that had persisted for 9 months. No other clinical symptom was observed. Vertebral artery angiography revealed a saccular aneurysm of the right VA. Magnetic resonance (MR) imaging demonstrated that the aneurysm was compressing the root exit zone of the right facial nerve. Endovascular treatment of the VA aneurysm was performed while monitoring the patient's LSRs. During occlusion of the VA at sites distal and proximal to the aneurysm, the LSRs temporarily disappeared and then reappeared with a higher amplitude than those measured preceding their disappearance. The hemifacial spasm alleviated gradually and disappeared completely 6 months after treatment. The LSRs changed in parallel with the improvement in the patient's hemifacial spasms and eventually disappeared. No recurrence of symptoms has been noticed as of 18 months postoperatively. This is the first report of the use of LSR monitoring during endovascular surgery for an intracranial aneurysm that causes hemifacial spasm. Intraoperative and postoperative changes in the LSRs provided useful information regarding the pathophysiology of hemifacial spasm.