Acoustic neuroma is a benign proliferation of the Schwann cells that cover the vestibular branch of the eighth cranial nerve (CN VIII). Symptoms are commonly a result of compression of the acoustic branch of CN VIII, the facial nerve (CN VII), and the trigeminal nerve (CN V). The glossopharyngeal nerve (CN IX) and vagus nerve (CN X) are less commonly involved. In extreme cases, compression of the brainstem may lead to obstruction of CSF outflow and elevated intracranial pressure (ICP).

• Hearing loss, unilateral tinnitus, balance problems, vertigo, facial pain (trigeminal neuralgia) and weakness, difficulty swallowing, fullness or pain of the involved ear, and headache may occur.
• With elevated ICP, patients may also suffer from vomiting, fever, and visual changes.
• Hearing loss is the most common presenting complaint and is usually high frequency.

The etiology is incompletely understood. Bilateral acoustic neuromas may be inherited in an autosomal dominant manner as part of neurofibromatosis type 2. This disease is associated with a defect on chromosome 22q1

DIFFERENTIAL DIAGNOSIS
Benign positional vertigo, Meniere’s disease, trigeminal neuralgia, cerebellar disease, normal-pressure hydrocephalus, presbycusis, glomus tumors, vertebrobasilar insufficiency, ototoxicity from medications, and other tumors: meningioma, glioma, facial nerve schwannoma, cavernous hemangioma, metastatic tumors
WORKUP
Physical examination, laboratory analysis, and imaging studies

• A detailed neurologic examination with special attention to the cranial nerves is crucial.
• Otoscopic evaluation may help to rule out other causes of hearing loss.
LABORATORY TESTS
CSF protein may be elevated.
IMAGING STUDIES
• CT scan with contrast can detect tumors 1 cm in diameter or larger ( Fig. 1–11 ).
• MRI with gadolinium is the most sensitive noninvasive test and can detect tumors as small as 2 mm in diameter.

Treatment decisions should be based on the size of the tumor, rate of growth (older patients tend to have slower-growing tumors), degree of neurologic deficit, life expectancy, age of the patient, and surgical risk.
• Surgery is the definitive treatment. Choice of approach (middle cranial fossa, translabyrinthine or posterior cranial fossa) may vary depending on the size of the tumor, amount of residual hearing, and degree of surgical risk that can be tolerated. Partial resection is sometimes undertaken to minimize the risk of injury to nearby structures. Intraoperative facial nerve monitoring is recommended.
• Radiotherapy has been used to treat tumors that are less than 3 cm in diameter. Radiotherapy following partial resection has also been used to minimize complications.
• Observation may be appropriate for older or frail patients with small tumors, but serial scanning may not be able to detect neurologically significant growth and risk may be higher if surgery is delayed.

Hearing can be preserved at near preoperative levels in more than two thirds of patients with small- to medium-sized tumors.

Prompt referral to an ENT specialist who is facile with all three surgical approaches is recommended.

Kondziolka D et al: Long-term outcomes after radiosurgery for acoustic neuromas, N Engl J Med 339:1426, 1999.

Pitts LH, Jackler RK: Treatment of acoustic neuromas, N Engl J Med 339:1471, 1998.

Poen JC et al: Fractionated stereotactic radiosurgery and preservation of hearing in patients with vestibular schwannoma: a preliminary report, Neurosurgery 45(6):1299, 1999.

Schmidt RJ et al: The sensitivity of auditory brainstem response testing for the diagnosis of acoustic neuroma, Arch Otolaryngol Head Neck Surg 127(1):19, 2001