Spatial Relationship between Hypoglossal Schwannoma and the Vertebral Artery Using the Far-Lateral Approach

In hypoglossal schwannoma removal via the far-lateral approach needs care as the vertebral arteries are usually adjacent to the tumors. Thus, it is important to understand their location respective to schwannoma to conduct a safe surgery. We reviewed the data of eight patients with hypoglossal schwannoma who underwent surgery in Keio University Hospital in 2005-2013. There were five males and three females (mean age at initial presentation was 48.6 years, range 38-72 years). We especially focused on the spatial relationship between the vertebral artery and the tumor, and evaluated their spatial relationship from intraoperative findings. All eight hypoglossal schwannomas included in the current study were type B according to Kaye's classification. As for spatial relationship between the tumor and the vertebral artery, in six out of eight cases, the vertebral artery was located inside or beneath the tumor; in contrast, in the other two cases, it was pushed out by the tumor and identified just after dural opening. Through the far-lateral approach, we found that the vertebral artery was located inside or beneath in most hypoglossal schwannoma; however, the vertebral artery was occasionally located on the tumor surface. From an anatomical perspective, we speculate this unique location of the vertebral artery in these cases is due to the unusual course of the hypoglossal nerve of tumor origin.