Acoustic Neuroma (Vestibular Schwanoma)
Dr. Fritsch is a member of the ANA (Acoustic Neuroma Association).
Acoustic neuroma, also known as vestibular schwanoma, is a benign intracranial tumor forming on the VIII cranial nerve. The VIII cranial nerve is specifically the balance and hearing nerve. These tumors most commonly originate from the vestibular (balance) portion of the VIII nerve from the Schwann cells. The Schwann cells are part of the external lining of the nerve. This type of Schwann tumor is generally slow growing, but puts pressure on surrounding structures intra-cranially.
The prevalence of acoustic neuroma is approximately one per 100,000 people. There are approximately 3,000 new acoustic neuromas diagnosed each year within the United States and it compromises approximately 7% of all intracranial tumors in adults. The peak incidents are in the fifth to sixth decades and both sexes are equally affected.
The signs and symptoms of acoustic neuroma are overwhelmingly those of ringing (tinnitus) of the ear and nerve type hearing loss. Small tumors start with these symptoms and larger tumors then progress to numbness in the face and facial nerve twitching or paralysis, as well as problems with swallowing and gag reflexes. Very large tumors may lead to increased intracranial pressure with headache, vomiting, and altered consciousness.
Causes of acoustic neuroma are not generally known and they occur only sporadically within the general population. There is, however, a related tumor is known as Neurofibromatosis and bilateral acoustic neuromas are very commonly seen and it is a hereditary familial problem. There are multiple other types of tumors which these patients may also have.
Diagnosis of acoustic neuromas initially begins with a history and physical examination, followed by otologic testing, and finally radiologic scanning. The most commonly used radiological scan is an MRI scan with gadolinium enhancement. On the scan, the tumor can be visualized, as well as its size and its shape.
Acoustic neuromas are generally slow growing tumors. Therefore, many patients are conservatively treated by an observation period. During the observation period, MRI scans are followed to estimate size progression. Many times patients in their elderly years or who are medically infirm will follow this route. Since the growth rate of an acoustic neuroma varies from tumor to tumor, close monitoring is necessary. In a younger person, it is already known that an observation period will eventually lead to definite treatment, because even a slow-growing tumor will enlarge during their lifetime to an unacceptable size.
Surgery of acoustic neuromas is a very direct route of removing the tumors. There are three main directions a surgeon may take to access the tumor. The route specifically taken for any individual depends on the patient’s age, health, and the size and shape of the tumor. Of the three surgical approaches, the most commonly used is the suboccipital approach. In this case, the tumor is approached from behind the ear. An other approach is the translabyrinthine approach, which goes directly through the ear and destroys the ear. It may be indicated if there is no hearing in the patient’s ear and, therefore, nothing to lose by drilling through the ear. The third approach is by the middle cranial fossa, which is reserved for small tumors in the lateral portion of the nerve. The suboccipital approach is very well tolerated and gives wide exposure of the tumor and can be used for all sizes of the tumors. It is generally a team approach between Otologist and Neurosurgeon.
The surgery risks for removal of the acoustic neuroma revolve mainly around the preservation of the facial nerve. In very small tumors, hearing may be preserved. The balance nerves on the affected side are resected with the tumor. The patient also must be aware that it is an intracranial procedure with attendant risks. There is a short intensive care unit stay after the surgery to monitor the patient.
Alternative treatment is Radiation Therapy. This is generally by Gamma-knife radiosurgery or Cyber-knife. The downsides for radiation therapy are induction of other tumors (such as glioblastoma) in the nearby irradiated tissue. As well, the swelling of the tumor may give rise to hearing loss and facial nerve problems. The radiation therapy is often times reserved for patients who are medically infirm and are not able to tolerate surgery. Additionally, long-term scanning is needed after radiation therapy since it does not kill the tumor, but generally “stuns” it. Progression of growth may occur followed by a surgical resection.
Overall, treatment for acoustic neuromas has progressed through specific, but well recognized treatment algorithms. The tumor resection is a common occurrence to physicians who specialize in Otology-Neurotology.