[A case of C2 neurinoma suffering syncopal episodes]

A 32-year-old male had a 4-year history of episodes of loss of consciousness. These episodes occurred several seconds after he would turn his head 60 degrees to the left, and had increased in frequency at the time previous to the operation he underwent. MRI revealed a round mass on the right side between the atlas and the axis. Cerebral angiography demonstrated that the right vertebral artery (VA) was occluded at the transverse foramen of the axis with the head rotated toward the left. The left VA was hypoplastic and no posterior communicating artery was visualized. A lateral surgical approach was performed between the left sternocleidomastoid muscle and the internal jugular vein. A yellowish and elastic but hard tumor was found to compress the VA. Postoperative MRI and vertebral angiography revealed neither residual tumor nor stenosis. Although the VA is frequently compressed by cervical tumors, only a few cases have been reported with tumors whose initial symptom was vertebro-basilar insufficiency. On the other hand, symptomatic stenotic change in the VA due to head movement can occur at the atlanto-axial joint and is named "bow hunter's stroke". In this case, flow of the VA was measured with an ultrasonic flowmeter after the tumor was removed. As the flow proved to change little during head rotation, additional decompression procedures such as removal of the transverse processes were judged unnecessary. Intraoperative arterial flow measurement has been found to be quite useful for evaluating the actual effect of surgical procedures.