What Is Acoustic Neuroma and How Does It Present?
Vestibular schwannoma develops from the Schwann cells of the balance-hearing nerve complex (the eighth cranial nerve) running from the inner ear to the brain. Most cases are one-sided and the cause is not fully known; the rare bilateral form is associated with a genetic disorder called neurofibromatosis type 2. The most typical first symptom is slowly progressive hearing loss in one ear, which may be accompanied by ringing in the ear and imbalance/dizziness. As the tumour grows it can press on the facial nerve and brainstem, causing facial numbness or, infrequently, facial weakness. Not everyone with one-sided hearing loss or tinnitus has a tumour, but these symptoms should be evaluated with contrast-enhanced internal-auditory-canal MRI; this imaging is the gold standard for diagnosis. Early diagnosis matters because it increases the chance of preserving hearing.
Sometimes the Right Decision: Surveillance (Watchful Waiting)
The benign and usually slow-growing nature of acoustic neuroma means not every tumour requires immediate treatment. Especially in small, asymptomatic or mildly symptomatic tumours, in elderly patients, or in those with a slow growth rate, a 'wait and scan' approach is a valid and frequently used strategy. In this approach the tumour is followed with MRI at set intervals (usually every 6–12 months); if it is not growing and symptoms are not worsening, active treatment is not needed. Many small tumours remain stable for years. A decision to observe protects the patient from the hearing or facial-nerve risk that unnecessary treatment would carry. However, follow-up must be carried out diligently: if the tumour begins to grow or symptoms progress, Gamma Knife or surgery is undertaken without delay. Surveillance is not 'refusing treatment' but an active, planned medical decision.
Gamma Knife Radiosurgery
Gamma Knife radiosurgery is an incision-free method that delivers highly focused radiation to the tumour in a single session, aiming to stop its growth. It is preferred especially in small and medium-sized tumours (generally under 2.5–3 cm) and its aim is not to 'destroy' the tumour but to control it by halting growth. Its most important advantages are that it is non-surgical, allows a quick return to daily life, and offers a relatively high chance of preserving existing hearing. The facial-nerve preservation rate is also high. Its limits are: it is not suitable for large tumours, its effect (cessation of growth) is assessed over time, there is a small chance the tumour will continue to grow despite radiation, and rarely hearing may decline over time. The choice between Gamma Knife and surgery is not governed by a single rule; tumour size, growth rate, hearing status and patient preference are weighed together.
Microsurgery: Removal of the Tumour
Microsurgery rests on removing the tumour under the microscope and is the preferred method especially in large tumours, in cases pressing on the brainstem or causing hydrocephalus, and in rapidly growing tumours. There are three main surgical approach routes (retrosigmoid, translabyrinthine, middle fossa), and which is chosen is determined by tumour size and the goal of preserving hearing. The most critical element of modern acoustic neuroma surgery is the continuous electrophysiological monitoring of the facial nerve and, where possible, the hearing nerve throughout the operation (neuromonitoring); this markedly reduces the risk of facial weakness. The advantage of surgery is that a tissue diagnosis is confirmed and a large tumour is directly removed. Its risks are hearing loss (common especially in large tumours), facial-nerve involvement, balance problems, CSF leak and general surgical risks. The procedure can take 4–8 hours; a few days of intensive care and a hospital stay of 5–7 days are usual.
Risks and Realistic Expectations
In treating acoustic neuroma the main goal is to control the tumour while preserving the facial nerve and, where possible, hearing; the balance between these goals varies with the method and tumour size. With surveillance the tumour may grow; with Gamma Knife hearing may decline over time or, with a small probability, the tumour may not be controlled; with surgery the risk of hearing loss and facial-nerve involvement is more pronounced, especially in large tumours. No method guarantees that 'hearing will be fully preserved' or that 'the tumour will never recur'. As a general rule, in small tumours the chance of preserving hearing is high, while in large tumours the priority is relieving brainstem compression and preserving the facial nerve. The right decision is made — assessing tumour size and growth rate, current hearing level, the patient's age and preferences — by a team in which ENT and neurosurgery work together. Expectations are shared openly before surgery or treatment.