Treatment The preferred treatment in most symptomatic cases has been surgical excision. Neurosurgeons who have had a lot of experience with these tumors favor a microsurgical suboccipital transmeatal approach (Martuza and Ojemann). The facial nerve can usually be preserved by intraoperative monitoring of brainstem auditory responses and facial nerve electromyography (EMG); in experienced hands, hearing can be preserved in approximately one-third of patients with tumors smaller than 2.5 cm in diameter. If no attempt is to be made to save hearing, small tumors can be removed safely by the translabyrinthine approach.
An alternative to surgery is focused radiation, which controls the growth of many of the smaller tumors. In a large series of patients treated with radiosurgery, facial motor and sensory functions were preserved in 75 percent of cases and, after 28 months of observation, no new neurologic deficits were detected (Kondziolka et al). This approach is favored in older patients with few symptoms but is being adopted increasingly for others. The rates of hearing loss and facial numbness and weakness are comparable or lower than with surgery, but the follow-up period in most series is less than 5 years (Flickinger et al). Focused radiation with the Gamma Knife or proton beam also appears to be preferable to surgery in cases of recurrent tumor. The antiangiogenic agent, bevacizumab, in preliminary reports has reduced the size of these tumors in patients with NF2 (Plotkin et al).
There is no consensus on the management of an incidentally identified tumor but it is reasonable to follow these with audiograms and serial imaging. Some authoritative sources suggest that half of lesions smaller than 2 cm in diameter will not progress, or do so slowly enough that hearing and balance are not impaired. However, lesions larger than this size are associated with more surgical complications and make sparing of hearing less likely.
Other Tumors of the Cerebellopontine Angle
Neurinoma or schwannoma of the trigeminal (gasserian) ganglion or neighboring cranial nerves and meningioma of the cerebellopontine angle may, in some instances, be indistinguishable from a vestibular schwannoma. Fifth cranial nerve tumors should always be considered if deafness, tinnitus, and lack of response to caloric stimulation (“dead labyrinth”) are not the initial symptoms of a cerebellopontine angle syndrome. A true cholesteatoma (epidermoid cyst) is a relatively rare tumor that is most often located in the cerebellopontine angle where it may simulate an acoustic neuroma but usually causes more severe facial weakness. Spillage of the contents of the cyst may produce intense chemical meningitis. Other disorders that enter into the differential diagnosis are glomus jugulare tumor (see later), metastatic cancer, neoplastic meningitis (especially lymphomatous), syphilitic meningitis, arachnoid cyst, and epidural plasmacytoma of the petrous bone. All these disorders may produce a cerebellopontine angle syndrome consisting of imbalance and unilateral hearing loss, but they are more likely to cause multiple lower cranial neuropathies and their temporal course differs from that of vestibular schwannoma. Occasionally, a tumor that originates in the pons or in the fourth ventricle (ependymoma, astrocytoma, papilloma, medulloblastoma) or a nasopharyngeal carcinoma may present as a cerebellopontine angle syndrome.
Craniopharyngioma (Suprasellar Epidermoid Cyst, Rathke Pouch or Hypophyseal Duct Tumor, Adamantinoma)