Although hearing loss impacts almost 50 Million people in the U.S. and is listed by the Department of Health and Human Services as the 3rd most common chronic disorder affecting older adults it is not often associated with tumors, lesions or growths in one’s head. More than 90% of hearing losses in the USA are attributed to a sensory deficit occurring within the cochlea (hearing organ) and or the neural pathway to the auditory cortex. Acoustic neuromas, also known as auditory nerve, VIIIth nerve tumors or vestibular schwannomas are classified as retrocochlear pathology since they exist beyond the cochlea in transition zones between the central and peripheral nervous systems along cranial nerve VIII.
What is acoustic neuroma (vestibular schwannoma)?
Acoustic neuromas go by many different names
- acoustic neurilemoma
- acoustic neurinoma
- fibroblastoma, perineural
- neurinoma of the acoustic nerve
- neurofibroma of the acoustic nerve
- schwannoma of the acoustic nerve
- vestibular schwannoma
Regardless of the name used, acoustic neuromas are benign, slow growing tumors that form along the branches of the eighth cranial nerve, also called the vestibulocochlear nerve. This nerve originates in the brain and leads to the inner ears where it then branches into divisions that are integral in both hearing and balance.
Acoustic neuromas are extremely rare, occurring only 1:100,000 people with 3,000 or less being identified annually. They are slow growing, non-cancerous, and almost always non-fatal unless they are left untreated. If acoustic neuromas are not identified or left untreated they essentially run out of space in the small internal auditory canal that connects the inner ear and the brain which leads to growth into the skull cavity. Additionally, when left untreated a dangerous amount of fluid can build up that could compress the brainstem and the cerebellum.
Acoustic neuromas are so slow growing in fact that oftentimes the treatment plan is no treatment at all but rather watchful monitoring via annual MRIs of the brain with and without contrast so that changes in size can be seen.
The exact cause of an acoustic neuroma is unknown and in most instances they occur spontaneously with no apparent reason. Additionally, no specific risk factors leading to the development of these tumors has been identified.
Symptoms of Acoustic Neuroma
In many patients, especially with small tumors, patients will be asymptomatic until the tumor is large enough, growing into a sensitive location in which it applies pressure to anatomy that then provokes symptoms.
The primary initial symptom (occurring in 90% of patients) is typically hearing loss in one ear, the ear affected by the tumor. This hearing loss is typically gradual but can be sudden although rarely. In some cases the hearing loss can fluctuate between improved and worsened states.
The second most common symptom is ringing in the ear (tinnitus) affected by the tumor. Additionally, a feeling of fullness in the affected ear is sometimes reported as is a difficulty understanding speech in the affected ear compared to the unaffected ear.
Acoustic neuromas can also impact a persons’ balance and may cause dizziness, disequilibrium or unsteadiness. Although rare, in some cases balance problems may present before hearing loss and tinnitus.
As acoustic neuromas become larger they can press against nearby cranial nerves resulting in additional symptoms. These additional symptoms consist of facial numbness, facial tingling, facial weakness, facial paralysis and swallowing difficulties.
In severe cases, typically cases that go unidentified or untreated for long periods of time, acoustic neuromas can apply pressure to the brainstem which prevents the normal flow of cerebrospinal fluid between the brain and spinal cord. As this fluid accumulates in the skull it can cause pressure on the tissues of the brain provoking multiple symptoms. These symptoms can include confusion, headaches and inability to control voluntary movements.
Causes of Acoustic Neuroma
Acoustic neuromas develop from a type of cell known as the Schwann cell that creates an insulating layer around nerves of the peripheral nervous system which includes cranial nerve VIII. Cranial nerve VIII divides into two branches, the cochlear branch, which sends sound to the brain and the vestibular branch, which transmits balance information to the brain. Schwann cells serve an invaluable protection service to nerves but in cases like acoustic neuroma the growth is uncontrolled and grow like a wart to produce the neuroma.
95% of acoustic neuromas occur randomly, almost always occur in one ear, are not due to hereditary causes and occur on the vestibular portion of the eighth cranial nerve.
The exact cause of an acoustic neuroma is unclear and no specific risk factors have been identified. Five percent of acoustic neuroma patients have an inherited acoustic neuroma in both ears that presents as part of neurofibromatosis type II (NF II).
Radiation exposure to the head, used to treat some cancers, has been linked to an increased incidence of acoustic neuroma. Cell phone usage has not been linked to acoustic neuromas.
Sex does not seem to impact the incidence of acoustic neuromas since they occur equally between men and women between the ages of 30-60.
What determines the acoustic neuroma treatment?
Treatment for acoustic neuroma is determined based on the size and impact that it is having on the patient. In most cases the first treatment is observation. Once confirmed via imaging studies a patient will typically receive annual hearing exams and periodic MRIs of the brain in order to monitor the size of the neuroma as well as its impact on a patients’ hearing. The hearing loss is typically treated via hearing devices including amplification and the use of CROS hearing systems in cases where the tumor has degraded the speech understanding ability of the affected ear beyond the capabilities of amplification.
Watching and waiting allows the patient to avoid possible complications of surgery and in the case of elderly patients an acoustic neuroma without severe symptoms may not require treatment during an individuals’ natural life expectancy. For younger patients, watching and waiting also makes sense as long as the acoustic neuroma is not life threatening.
Once an acoustic neuroma causes symptoms or becomes life threatening microsurgery or radiation therapy may be considered. The location and size of an acoustic neuroma as well as hearing level and general health are weighed in when determining which treatment method is used.
Microsurgery is performed utilizing specialized instruments under a microscope that allows the surgeon to perform surgery on very small body parts.
During microsurgery, the surgeon may remove all or part of the acoustic neuroma. Partial tumor removal occurs to reduce the risk of unwanted complications from the surgery. Partial removal is typically easier and safer compared to a full removal. Obviously as the tumor grows post surgery additional may be necessary.
When a complete tumor removal is needed great care is taken to protect the facial nerve and avoid facial paralysis. Additionally, preserving hearing is considered a priority as well.
Radiation Therapy is the three dimensional focusing of radiation on the affected sites with the goal of effectively dosing the tumor cells of the affected ear with minimal damage to surrounding cells. Radiation therapy can stop or slow the growth of a tumor. Additionally, radiation therapy is a noninvasive treatment option that can be effective, albeit longer in some cases compared to microsurgery.
What if an acoustic neuroma returns after radiosurgery?
Should an acoustic neuroma return after radiosurgery it will be observed as it was before and the appropriate treatment will be determined based on its size, location and life threatening status to the patient.
Acoustic Neuroma FAQs
Are acoustic neuromas dangerous?
Acoustic neuromas are dangerous. Even a small acoustic neuroma that is not growing can damage hearing and balance leading to decreased connection to people and increased fall risk.
As acoustic neuromas grow and if left untreated, fluid can build up in the brain that can cause compression of the brainstem and the cerebellum. .
Are acoustic neuromas hereditary?
Five percent of acoustic neuroma patients have an inherited acoustic neuroma in both ears that presents as part of neurofibromatosis type II (NF II).
The other 95% of acoustic neuromas occur randomly, almost always occur in one ear, are not due to hereditary causes and occur on the vestibular portion of the eighth cranial nerve.
Complications of Acoustic Neuroma
Patients undergoing either microsurgery or radiation may experience post-treatment complications to include: Cerebrospinal fluid leakage or an infection that produces meningitis although rare may occur. obstruction of the flow of cerebrospinal fluid can occur. Decreased mental alertness due to blood clots. Headaches. Fascial weakness. Facial numbness. Hearing loss. Dizziness.
The facial nerve may be damaged by the acoustic neuroma or by surgery.
Eye problems may develop in some individuals following surgical removal of an acoustic neuroma.
Facial weakness can cause incomplete eyelid closure leading to irritation of the cornea. Double vision may occur if there is pressure applied to cranial nerve VI. Additionally, there could be impairment to the eyelid muscles requiring the use of artificial tears and / or lubricants.