What Is an Acoustic Neuroma?
An acoustic neuroma arises from the Schwann cells around the balance branch (vestibular nerve) of the eighth cranial nerve; this is why its correct name is vestibular schwannoma. Almost all are benign, do not spread elsewhere in the body and usually grow slowly. They begin in the internal auditory canal and can grow towards the cerebellopontine angle between the brainstem and cerebellum. As they enlarge they can press, beyond the hearing and balance nerve, on the facial nerve, and in advanced cases on the brainstem and the flow of cerebrospinal fluid. Most cases are one-sided; a bilateral acoustic neuroma suggests neurofibromatosis type 2, a rare genetic disorder.
Symptoms and Diagnosis
The most typical and earliest symptom is slowly progressive one-sided hearing loss and ringing (tinnitus) in the same ear; over time unsteadiness and dizziness may be added. If the tumor grows, numbness or twitching of the face (involvement of the facial and trigeminal nerves) can occur. For this reason unexplained one-sided hearing loss should always be taken seriously and investigated. The gold standard of diagnosis is a contrast-enhanced thin-slice MRI focused on the internal auditory canal; even small tumors can be seen with this study. A hearing test (audiometry) contributes both to the diagnosis and to the treatment decision, because the state of existing hearing is an important factor in choosing the treatment.
Three Main Options: Observation, Gamma Knife, Microsurgery
There is no single correct treatment for acoustic neuroma; the decision is made according to tumor size, growth rate, the patient's age, existing hearing and symptoms. Observation (wait-and-scan): especially for small, asymptomatic tumors or those in older patients, follow-up with interval MRI is an appropriate option, because most tumors grow very slowly or not at all. Gamma Knife / stereotactic radiosurgery: for small-to-medium tumors, it aims to stop tumor growth with radiation; it is not surgery, is usually given on an outpatient basis, and the chance of preserving hearing is reasonable within certain limits. Microsurgery: for large tumors pressing on the brainstem or growing rapidly, it is performed to remove the tumor; with the microscope and nerve monitoring, the facial nerve in particular is protected. These three options are not rivals but the right tool for the right patient.
The Microsurgical Process and Recovery
When surgery is chosen, different surgical routes (retrosigmoid, translabyrinthine, middle fossa) may be selected according to tumor size and existing hearing. The operation is performed under general anaesthesia, under the microscope and with neuromonitoring that continuously watches the facial nerve; the aim is to preserve the function of the facial nerve and, where possible, hearing while removing the tumor. The procedure can take several hours depending on tumor size. It is usually followed by one to two days of intensive care and a hospital stay of a few days. Balance may be affected for a time in the early period; the brain adapts to this over time and balance rehabilitation speeds up the process. The tumor is monitored with a control MRI.
Risks and Realistic Expectations
Although an acoustic neuroma is benign, treatment decisions require an honest discussion of risk. The main risks are reduction or loss of hearing on the operated side, facial nerve weakness, balance problems and, more rarely, a cerebrospinal fluid leak; these risks increase as tumor size grows. For this reason the chance of preserving hearing in small tumors is markedly higher than in large ones, and early diagnosis matters. With Gamma Knife the aim in most patients is to stop tumor growth; shrinkage is not always expected. No method guarantees that hearing will be preserved. The most suitable option for you is shared openly before surgery, with realistic expectations, according to tumor size, your hearing status and your preference.