Neurofibromatosis type 2 (NF2)
Incidence
It occurs with an incidence of 1:40,000. It is an autosomal dominant disorder characterized by bilateral Schwann-cell tumors of the vestibular branch of the eighth cranial nerve, vestibular schwannomas, in 95 percent of gene carriers.
Clinical Characteristics
Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder characterized by bilateral Schwann-cell tumors of the vestibular branch of the eighth cranial nerve, vestibular schwannomas, in 95 percent of gene carriers. Additional findings include subcapsular cataracts, occasional cafe café au lait spots, and meningiomas or ependymomas. This condition is considered a neurocutaneous syndrome or phakomatosis. The diagnosis is usually made on the basis of family history, hearing loss, or associated brain-stem findings secondary to the mass effect of vestibular schwannomas. Gadolinium-enhanced MRI is the most definitive test to confirm the presence of a vestibular schwannoma. Symptoms of vestibular schwannomas (formerly called acoustic neuromas) are usually caused by pressure from the tumors and most often develop during the second or third decade. The first symptom in NF2 is typically hearing loss, which is generally unilateral but may be symmetric. A frequently reported symptom is distorted sound perception when using the telephone. The hearing loss is usually progressive; however, approximately 10 percent of patients report sudden hearing loss. Other, less commonly reported symptoms, include ringing or roaring in one or both ears, with or without dizziness or unsteadiness.
Other findings related to compression by the tumor mass on neighboring structures may include facial weakness, sensory changes, ataxia, headache, or diplopia. Juvenile lens opacities or subcapsular cataracts are estimated to occur in half of NF2 patients and may precede the onset of other symptoms, allowing early identification of affected individuals. NF2 patients may have cafe café au lait spots and skin neurofibromas but typically these are much less common in NF2 than in NF1. Tumors of the brain, spinal cord, and peripheral nerve are commonly seen in NF2. Schwann-cell tumors are the most common, but tumors of meningeal and glial origin may also be found in the same patient. Penetrance is high in FN2, such that individuals carrying a mutant allele have a 95 percent chance of bilateral vestibular schwannomas developing. The ideal treatment for symptomatic patients is the total excision of the tumor with minimal morbidity and mortality. Other management options include observation, subtotal removal, and radiation. Selection of the treatment option is typically based on the clinical findings, patients\' age, and size and growth rate of the tumor. Surgery is clearly indicated in a young patient with evidence of tumor growth or a progressive neurologic deficit. On the other hand, long-term observation is appropriate for the elderly patient without severe neurologic deficits or evidence of tumor growth and for patients with imperfect but stable and useful hearing and no evidence of tumor progression. The use of gadolinium-enhanced MRI has resulted in the identification of patients with very small, relatively asymptomatic vestibular schwannomas. Given that the natural history for these patients is still not known, conservative management may be more appropriate.
Precipitants
no
Provocation Tests
no
Diagnostic Procedures
Early diagnosis of vestibular schwannomas is critical for successful treatment. The diagnosis of NF2 should be suspected in the following instances: in the parent, sib, or child of a person with NF2; in a person with an apparent unilateral vestibular schwannoma and onset of symptoms before 30 years of age (because sporadic vestibular schwannomas present later in life); in a child with meningeal or Schwann-cell tumor; in an individual of any age with multiple nervous system tumors of unknown etiology; and in a person with a few cafe café au lait spots, one or more neurofibromas, no Lisch nodules, and a negative family history for NF1. Such individuals require detailed evaluation, including careful skin and eye examination, audiologic evaluation, and neuroimaging of the head if indicated. Brain-stem auditory evoked responses (BAER) are ideal for the evaluation of audiologic dysfunction. The sensitivity of the BAER test is 94 percent, and the specificity is greater than 85 percent for the diagnosis of vestibular schwannoma. MRI is considered the most definitive test to confirm or rule out the presence of a vestibular schwannoma.