Acoustic neuromas are the most common tumours in the cerebellopontine angle. They are benign and arise from the Schwann cells of the vestibular nerve in the internal auditory canal. Their growth rate is variable (0–10 mm/year), but they usually grow slowly, gradually extending into the posterior fossa from the internal auditory meatus. Most patients have no family history of schwannoma, and present with a unilateral tumour. Bilateral acoustic neuromas may occur in patients with neurofibromatosis type II, in whom there is usually a family history of the disease. Such patients often suffer from other tumours of the central nervous system.

The first symptom noted by most patients is a gradual loss of hearing. Difficulty in understanding words, often first noted when using the telephone, is frequently recorded in the history. In a few patients the hearing loss may be sudden or may fluctuate. Tinnitus is also a common symptom. Dizziness, unsteadiness, vertigo, and fullness or discomfort in the ear may be noted.

As the tumour grows into the posterior fossa numbness of the face may occur due to compression of the fifth cranial nerve. Occasionally tic-like facial pain occurs. Although the facial nerve is always compressed by the tumour, symptoms related to this nerve are not common. Large tumours may cause difficulty with balance and co-ordination, diplopia, trouble in swallowing, or hydrocephalus. Hearing loss may be the only symptom, however, even in a patient with a large tumour.

The pure-tone audiogram usually shows a high frequency hearing loss, but there is no diagnostic pattern and occasionally the study is normal. Speech discrimination is usually reduced, and the results of brain-stem auditory evoked response testing are abnormal in almost all patients. The diagnosis is established by MRI with gadolinium enhancement (Fig. 1) 2286. The MRI scan clearly shows tumours as small as a few millimetres in diameter (Fig. 2) 2287. CT scanning with intravenous contrast defines many tumours, but often misses small acoustic neuromas. Most tumours are solid, but a few have a cystic component.

Three treatment options are available. For most patients the recommended treatment is surgery. Careful preoperative preparation, the use of microneurosurgical techniques, excellent neuroanaesthesia, and specialized postoperative care have significantly reduced the incidence of mortality and serious morbidity associated with such surgery. Focused radiation therapy has been used to treat enlarging tumours in some elderly patients and those with recurrent tumours. MRI scans and periodic clinical evaluation may be recommended in some patients who have a long clinical history and only hearing loss, those with minimal symptoms, and in some elderly patients in whom the growth rate may be slower.

The acoustic neuroma is usually approached via a suboccipital craniotomy: this is the safest method for tumours that extend more than 1 cm into the posterior fossa. It is also used in all patients in whom an attempt is being made to save hearing. A translabyrinthine approach may be used for the resection of small tumours in patients with no useful hearing. Some surgeons use the translabyrinthine or combined translabyrinthine-suboccipital approach for excision of large tumours.

Preservation of the facial nerve is now possible in a high percentage of patients, although some, especially those with large tumours, may suffer temporary facial paralysis which can take up to a year to recover. A high percentage of patients with small (extension into the posterior fossa of less than 1.5 cm) or medium (1.5–2.5 cm) tumours retain good facial nerve function, and more than half of those with large tumours make a good recovery. Preservation of facial nerve function is helped by the use of intra-operative monitoring.

Cochlear nerve function can be preserved in some patients with small tumours and who have reasonable hearing before surgery. The ability to hear depends not only on the integrity of the cochlear nerve, but also on the internal auditory blood supply that enters through the internal auditory canal. Continuous intra-operative monitoring of auditory nerve function may help to preserve hearing.

Ojemann RG, Martuza RL. Acoustic neuroma. In Youmans JR, ed. Neurological Surgery (3rd edn) Philadelphia: W. B. Saunders, 1990: 3316–50.

Ojemann RG, Levine RA, Montgomery WM, McGaffign P. Use of intraoperative auditory evoked potentials to preserve hearing in unilateral acoustic neuroma removal. J Neurosurg 1984; 61: 938–48.