Hypoglossal schwannomas are extremely rare benign tumors arising from Schwann cells of the 12th cranial nerve. Surgical management of hypoglossal schwannomas requires detailed knowledge of the anatomy around the lower cerebellopontine angle (CPA), the craniovertebral junction (CVJ), and high cervical regions. If a tumor extends through the hypoglossal canal to the extracranial space, the canal is exposed by drilling the posterior half of the occipital condyle (OC), maintaining craniovertebral stability. Based on our experience and a literature review, we proposed the following modified grading scale to facilitate surgical planning: Type A, intradural tumors; Type B, dumbbell-shaped tumors; Type C, extracranial tumors; and Type D, peripheral tumors. The standard lateral suboccipital approach without opening the foramen magnum (FM) does not always provide adequate operative exposure for intradural type tumors. The transcondylar approach with FM opening and high cervical exposure allows gross total resection of dumbbell-shaped tumors. This specific skull base approach consists of an extended lateral suboccipital craniectomy with partial removal of the OC, which provides a wider view of the lower CPA without excessive cerebellar retraction. Key techniques leading to good outcomes are drilling of the OC, soft tissue dissection around the vertebral artery, and accurate exposure of the anterolateral CVJ.
Yoichi Nonaka (Tue,) studied this question.