An acoustic neuroma--also known as an acoustic neurinoma, acoustic neurilemoma or vestibular schwannoma--is a slow-growing, noncancerous tumor on the nerves of the inner ear. As the tumor grows, it can interfere with the normal function of the inner ear, disrupting balance and hearing. Large tumors can impinge on the nerves of the face or press on the brain stem or cerebellum with life-threatening consequences, but fortunately these are rare, according to the Mayo Clinic.
Physiology
At the inner ear, the eighth cranial nerve splits into divisions called the cochlear, superior vestibular and inferior vestibular branches. The cochlear branch serves as the hearing apparatus while the vestibular branches carry spatial information that maintains balance. An acoustic neuroma is also known as a vestibular schwannoma because it develops in the insulating Schwann cells enveloping the electrical impulse-conducting fibers of a vestibular branch. Close association of the nerves means that a tumor on one affects the function of the others.
Symptoms
Small acoustic neuromas can cause subtle disturbances in hearing and balance. In addition to dizzy spells, a patient might notice hearing loss and ringing or buzzing--a symptom called tinnitus--in one ear. The hearing symptoms affect only one ear and do not switch sides. Larger tumors that press on the nerves serving the muscles of the face can cause one-sided facial numbness or paralysis occurring on the same side as the hearing loss.
Diagnosis
The National Institute on Deafness and Other Communication Disorders stresses that asymmetry is a key feature of acoustic neuroma; the symptoms occur in one ear and do not switch sides because in the vast majority of cases there is only one tumor. However, the early symptoms of hearing loss, tinnitus and dizziness can occur in many other common conditions of the inner ear, necessitating several tests for an accurate diagnosis. In addition to hearing tests, a doctor might order a CT scan or MRI to pinpoint the tumor’s location.
Hearing Loss
In general, hearing loss induced by an acoustic neuroma is one-sided and slowly progressive. As the tumor grows, auditory nerve function declines and hearing worsens, potentially causing deafness in that ear. Rarely, sudden hearing loss occurs with acoustic neuroma. Other rare cases can have bilateral symptoms of hearing loss and tinnitus in both ears: those cases usually result from a genetic disorder called neurofibromatosis type 2 that predisposes patients to development of multiple neural tumors.
Treatment
Slow-growing tumors causing minor symptoms can be carefully monitored but otherwise left untreated. In that case, patients can expect their hearing loss to gradually worsen. The viability of other options, including radiation treatment to kill the tumor or surgery to remove it, depends on the location and size of the tumor. Removing the tumor risks damaging the associated nerve, causing permanent hearing loss.
