Facial neuropathy due to axonal degeneration and microvasculitis following gamma knife surgery for vestibular schwannoma: a histological analysis. Case report.

Complete facial palsy (House-Brackmann Grade VI) developed in a 63-year-old man with a vestibular schwannoma 25 months after he had undergone two gamma knife surgeries performed 33 months apart and involving a cumulative dose of 24 Gy directed to the tumor margin at the 50% isodose line. Magnetic resonance imaging demonstrated tumor enlargement with central nonenhancement, which initially had been recognized 21 months after the second radiosurgery. Microsurgery was performed to achieve total removal of the tumor. Histological and immunohistochemical examinations of the facial nerve specimen removed from the edge of the tumor revealed a loss of axons, proliferation of Schwann cells, and microvasculitis. In this case, microvasculitis and axonal degeneration were probably the major causes of the radiation-induced facial neuropathy.