An acoustic neuroma, also known as a vestibular schwannoma, is a rare, non-cancerous (benign) tumor that develops on the main nerve leading from your inner ear to your brain. This nerve, called the vestibulocochlear nerve (or 8th cranial nerve), has two parts: one involved in hearing and the other in balance. As the tumor grows, it can press on these nerves, leading to hearing loss, tinnitus, balance problems, and other symptoms.
Causes:
The exact cause of most acoustic neuromas is unknown. However, about 5-10% of cases are associated with a genetic disorder called Neurofibromatosis Type 2 (NF2).
- Sporadic Acoustic Neuroma: The majority of cases (90-95%) are sporadic, meaning they occur randomly with no clear genetic link or family history. They are believed to result from a spontaneous mutation in a gene on chromosome 22 that helps produce a tumor-suppressor protein (merlin or schwannomin).
- Neurofibromatosis Type 2 (NF2): This is an inherited genetic disorder that causes tumors to grow on nerve tissue throughout the body. Individuals with NF2 typically develop bilateral acoustic neuromas (tumors on both hearing/balance nerves) and are often diagnosed at a younger age. NF2 is caused by a mutation in the NF2 gene.
- Radiation Exposure: While rare, exposure to radiation, particularly to the head and neck, has been linked to an increased risk.
- Age: Acoustic neuromas are most commonly diagnosed in people between the ages of 30 and 60.
Symptoms:
Symptoms of an acoustic neuroma typically develop slowly over months or years as the tumor gradually grows and presses on the vestibulocochlear nerve and surrounding brain structures. The earliest symptoms are often related to hearing and balance.
- Hearing Loss:
- Gradual, progressive hearing loss in one ear: This is the most common initial symptom, often affecting high frequencies first.
- Difficulty understanding speech, especially in noisy environments.
- Hearing loss can sometimes be sudden.
- Tinnitus: Ringing, buzzing, roaring, or hissing sound in the affected ear.
- Balance Problems and Dizziness:
- Feeling unsteady, uncoordinated.
- Occasional dizziness or vertigo (sensation of spinning).
- Difficulty walking in a straight line.
- Facial Numbness or Weakness: As the tumor grows, it can press on the trigeminal nerve (causing facial numbness, tingling, or pain) or the facial nerve (leading to facial weakness or paralysis on the affected side).
- Headaches: May occur as the tumor grows larger.
- Ear fullness or pressure.
- Double vision (diplopia) or other eye problems: Less common, usually with very large tumors affecting other cranial nerves.
- Swallowing difficulties (dysphagia) or hoarseness: Rare, with very large tumors.
Diagnosis:
Diagnosing an acoustic neuroma requires a comprehensive evaluation, as early symptoms can be subtle or mistaken for other conditions.
Medical History and Physical Exam: The doctor will ask about your symptoms, medical history, and perform a neurological exam, checking hearing, balance, and facial sensation/movement.
Hearing Test (Audiometry): This is typically the first test. It can confirm hearing loss and its pattern (often asymmetrical, affecting one ear more than the other), which is a key indicator.
- Brain Imaging (Crucial):
- MRI (Magnetic Resonance Imaging) with gadolinium contrast: This is the gold standard for diagnosing acoustic neuroma. It provides detailed images of the brain and inner ear, clearly showing the tumor’s size, location, and relationship to surrounding structures.
- CT scan (Computed Tomography): Less detailed than MRI but may be used if MRI is contraindicated.
- Auditory Brainstem Response (ABR) Test: Measures how the brain responds to sounds, assessing the function of the hearing nerve. This can help detect problems in the nerve pathway.
- Vestibular Tests: (e.g., Videonystagmography – VNG) To assess balance function and detect abnormalities.
Treatment:
Treatment for acoustic neuroma depends on the tumor’s size, growth rate, the patient’s age, overall health, and symptoms. Since they are benign, the goal is to control growth, preserve nerve function, and manage symptoms.
- Observation (“Watch and Wait”):
- For small tumors, slow-growing tumors, or in older patients with minimal symptoms, close monitoring with regular MRI scans is often the initial approach.
- The goal is to avoid unnecessary intervention if the tumor is not causing problems.
- Radiation Therapy (Stereotactic Radiosurgery/Radiotherapy):
- Uses highly focused beams of radiation to target the tumor, aiming to stop its growth or cause it to shrink.
- Examples include Gamma Knife, CyberKnife, and proton beam therapy.
- Often preferred for small to medium-sized tumors or in patients who are not candidates for surgery. It aims to preserve hearing and facial nerve function.
- Surgery (Microsurgical Resection):
- Involves surgically removing the tumor. This is typically done by a neurosurgeon or neuro-otologist.
- The approach chosen depends on tumor size, location, and surgeon preference (e.g., translabyrinthine, retrosigmoid, middle fossa).
- Surgery is often considered for larger tumors that are causing significant symptoms or are growing rapidly.
- Risks include hearing loss, facial weakness, and balance problems.
- Symptomatic Management:
- Hearing aids: For hearing loss.
- Tinnitus management: Sound therapy, counseling (CBT), or masking devices.
- Vestibular rehabilitation therapy (VRT): Exercises to help improve balance and reduce dizziness.
The choice of treatment is a complex decision made in consultation with a multidisciplinary team including neurosurgeons, otolaryngologists (ENTs), radiation oncologists, and audiologists.
