Neurofibromatosis type 2 - Hereditary and congenital disorders

Neurofibromatosis type 2

Definition

Autosomal dominant condition characterised by the development of bilateral acoustic neuromas.

Incidence

1 in 100,000 individuals.

Aetiology

An autosomal dominant condition caused by a mutation in the NF2 gene on chromosome 22 which codes for a protein termed schwannomin or merlin. This protein acts as a tumour suppressor gene by an unknown mechanism.

Pathophysiology

Schwannomin has similarities with cytoskeletal components that link to the actin/spectrin complex, it is therefore suggested that the cell–cell interaction is abnormal and hence contact inhibition is prevented.

Clinical features

Patients may have a few, large cafe´ au lait spots. Unlike NF1 the main feature is bilateral acoustic neuromas. The earliest presenting symptom is unilateral hearing loss or tinnitus. Hearing loss may be sudden, vertigo is rare, patients with large tumours experience headaches, visual disturbances, and ataxia.

Complications

Patients also have a tendency to form other brain tumours such as meningiomas and gliomas.

Investigations

Pure tone audiometry reveals unilateral or asymmetrical sensorineural hearing loss, electric response audiometry shows characteristic prolonged I–V latency differentiating the hearing loss from cochlear deafness. CT and MRI are definitive.

Management

Surgical resection is the preferred treatment via neurosurgicalotological approach by translabyrinthine or suboccipital approach with facial nerve monitoring. Radiotherapy is used in patients unfit for surgery.