An acoustic neuroma, also called vestibular schwannoma, is a benign, slow-growing tumor that arises from the Schwann cells forming the sheath (covering) of the vestibulocochlear nerve. As the tumor grows, it expands from its origin inside the internal auditory canal out into the space between the brainstem and the bone known as the cerebellopontine angle. The pear-shaped tumor can continue to enlarge, compressing the trigeminal nerve, which is responsible for facial sensation. Eventually, the tumor can compress the brainstem. Acoustic neuromas are classified according to their size as small (less than 1.5 cm), medium (1.5 to 2.5 cm), or large (more than 2.5 cm)
The symptoms caused by an acoustic neuroma follow the size and growth of the tumor. The most common first symptom is hearing loss in the affected ear, which often goes unrecognized or is mistaken for a normal change of aging. Small tumors, which are typically limited to the bony canal, cause hearing loss in one ear, tinnitus (ringing in the ears), and unsteadiness or dizziness. As the tumor expands, hearing loss may worsen, facial weakness may occur, and balance problems (disequilibrium) may occur. Large tumors can compress the brainstem (causing imbalance) and the trigeminal nerve (causing facial numbness). As brainstem compression becomes severe, the fourth ventricle collapses and hydrocephalus results, causing persistent headache and visual problems.
Acoustic neuromas affect about 10 people in one million. More women than men are affected. Patients are usually diagnosed between 30 to 60 years of age.
The cause of acoustic neuromas is largely unknown. No environmental factor (such as cell phones or diet) has been scientifically proven to cause these tumors. Acoustic neuromas can be sporadic or caused by an inherited condition called neurofibromatosis type 2 (NF-2). Sporadic tumors occur 95% of the time, while 5% of acoustic neuromas occur with NF-2.
Neurofibromatosis is a rare disease that occurs in two forms. Type 1 causes tumors to grow on nerves throughout the body, especially the skin. Type 2 can cause acoustic neuromas on both the left and right sides, creating the possibility of complete deafness if the tumors grow unchecked. The presence of bilateral acoustic tumors affects the choice of treatment, as hearing preservation is a prime objective.
The treatment that is right for you will depend on your age, general health, hearing status, and the tumor size. The larger the tumor, the more complex the treatment. Therefore, early recognition, diagnosis, and treatment are essential. Because patients and acoustic neuromas differ, it is important to seek treatment at a medical center that offers the full range of options, including surgery, radiosurgery, and hearing or facial rehabilitation. A neurosurgeon, otologic surgeon, and radiation oncologist work as a team to treat acoustic neuromas.
The doctor will ask about your personal and family medical history and will perform a complete physical examination. In addition to checking your general health, the doctor will perform a neurological exam. This will include checks for mental status and memory, cranial nerve function (sight, hearing, smell, tongue and facial movement), muscle strength, coordination, reflexes, and response to pain. Diagnostic tests may include:
Audiogram is a hearing test performed by an audiologist. During the test you will wear earphones and hear a range of sounds at different tones directed to one ear at a time. Also, speech discrimination will be assessed. The test can detect whether you have hearing loss that is sensorineural (from nerve damage) or conductive (from eardrum or ossicle damage).
Electronystagmography (ENG) is a test that evaluates your balance by detecting eye movements while stressing your balance in various ways. During ENG, eye movements are recorded with small electrodes placed on the skin around the eyes. Alternatively, eye movements may be recorded by videonystagmography (VNG), using an infrared video camera mounted inside goggles that you wear.
Magnetic Resonance Imaging (MRI) is a noninvasive test that uses a magnetic field and radiofrequency waves to give a detailed view of the soft tissues of the brain. A contrast dye called gadolinium may be injected into the bloodstream during scanning to make tumors more visible. MRI is useful in evaluating lesions and their effects on surrounding brain structures (Fig. 2).
Computed Tomography (CT) is a noninvasive test that uses X-rays and a computer to view anatomical structures within the brain. It is especially useful for viewing changes in bony structures, such as widening of the internal auditory canal.
Auditory Brainstem Response (ABR) is a test that checks the hearing pathway to the brainstem. Electrodes on the scalp and earlobes capture the brain’s responses to clicking noises heard through earphones.