Clipping of a vertebral artery aneurysm behind the hypoglossal nerve under the monitoring of lower cranial nerves

Under an operative view, an aneurysm of the vertebral artery is located behind the lower cranial nerves. To prevent neurological deficits we employed electrophysiological monitoring while clipping an aneurysm of the vertebral artery. A 64-year-old woman had suffered a sudden severe headache in the morning. Computed tomography (CT) revealed a subarachnoid hemorrhage (SAH) and CT angiography revealed an aneurysm at a branching point of the left vertebral artery. The condylar fossa approach was taken while recording electromyography (EMG) of the lower cranial nerves. The aneurysm was located just behind the hypoglossal nerve and could not be clipped without strong traction of the hypoglossal nerve. Therefore, the hypoglossal nerve was divided to separate the lower two bundles of the hypoglossal nerve from the other bundles, and the clip was applied to the aneurysm between the nerve bundles without any change of the tongue EMG. The patient went home 10 days after operation with no neurological deficit. In conclusion, we report a case of a ruptured aneurysm of a vertebral artery, which was clipped while monitoring the lower cranial nerves. Tongue EMG monitoring enabled us to clip the aneurysm without nerve injury and revealed that the hypoglossal nerve near the hypoglossal canal can be divided into several bands without neurological deficit.