Acoustic neuromas are tumors of the balance nerves. They are also called vestibular schwannomas.
You may reference the Anatomy of the Ear page for better understanding of the anatomy.
Patients most commonly present with a one-sided or asymmetric hearing loss. Other common presenting symptoms include, one-sided tinnitus (ringing in the ear), balance problems, facial numbness. Sudden hearing loss is another presenting symptom of acoustic neuromas.
The cause of acoustic neuroma is unknown. It is thought to be due to a genetic error. In patients with a rare disorder, called neurofibromatosis type 2, a gene error has been identified.
Acoustic neuromas are uncommon tumors. It occurs in approximately 6 to 10/million people per year. That means that in Orange County and surrounding area, there are approximately 50-80 patients per year who are diagnosed with acoustic neuromas per year. It is thought to be caused by an error that occurs in one of the genes. There is a hereditary form of the disease called neurofibromatosis type II, in which patients develop tumors on both sides.
Generally after a complete history and physical exam, some tests need to be performed to diagnose otosclerosis. A test of the hearing (audiogram and tympanogram) and MRI scan (special imaging study of the nerves of balance and hearing) and a CT scan (special 3-dimensional x-ray) of the temporal bone (ear bone) is necessary for diagnosis and to rule out other causes of the hearing loss.
There are 3 options for the treatment of acoustic neuromas.
1. Watchful waiting. Older patients (over 65) with small tumors (less than 1 cm [1/2 inch]) or those with multiple medical problems are the patients who are sometimes observed. The patients who are selected for watchful-waiting need MRI (special imaging technique) scans done every 6 to 12 months to observe the tumor to see if it grows. If there is a sign of growth, then either radiation or surgery will be selected for their treatment.
2. Stereotactic Radiation (also called stereotactic radiosurgery, Gamma Knife, or Cyberknife). Patients with small and medium sized tumors (less than 3 cm) in older patients (over 65) or any patient who has medical problems (such as heart disease, etc) that prevent undergoing surgery are the best candidates for radiation. Younger patients who desire, may also undergo stereotactic radiation. The radiation is given by one of several methods: Linear accelerator, Gamma Knife, or Cyberknife. Radiation therapy is effective in stopping the growth of 95% of tumors. The most common side effects of radiation include facial paralysis, facial numbness, hydrocephalus (increased fluid pressure in the brain), deafness, among others. At least half of the patients whose tumors grow after radiation will need surgery. Those patients who need surgery after radiation generally have poor facial nerve function because radiation leads to scarring of the tumor. The long-term consequences of stereotactic radiation to acoustic neuromas are not known. Click here for more information on stereotactic radiation.
Dr. Djalilian, the director of neurotology-skull base surgery performs CyberKnife for acoustic neuromas.
Dr. Linskey, chairman of neurosurgery and a member of the skull base team, is an expert in Gamma Knife radiation for treatment of acoustic neuromas.
3. Surgical resection. Surgery has for many years been the standard of care for the treatment of acoustic neuromas. There are 3 main surgical approaches for the treatment of acoustic neuromas. The type of approach depends on the size of the tumor and the patient’s hearing.
You may reference the Anatomy of the Ear page for better understanding of the anatomy.
The middle fossa approach is used for small tumors under 15 millimeters (3/5th of an inch) in patients who have useful hearing (see figure below). The approach involves an incision in front of the ear in the hairline and removal of the tumor from above. Hearing is preserved in 60-70% of patients. Using endoscopes for tumor removal can increase the likelihood of preserving hearing..
The MRI of a patient with a small acoustic neuroma who was treated with a middle fossa approach by Dr. Djalilian and had preservation of hearing. The image is a vertical slice of the head. The ears are on the two sides. The top of the head is at the top of the picture, and the neck is on the bottom of the picture. The arrows indicate the approach coming from above the ear to reach the tumor (the bright area at the end of the arrows).
The retrosigmoid approach (sometimes called the suboccipital approach) is used in patients with hearing who have larger tumors than those treated with the middle fossa approach. The tumor is approached from behind the sigmoid sinus (a vein in the brain) and the inner ear is not disturbed. Hearing is preserved in about 50% of cases. Endoscopes can be used to remove tumors to increase the likelihood of preserving hearing.
This approach is primarily used in patients who have lost all useful hearing in the ear affected by the tumor. In this approach, the tumor is removed by approaching it through the inner ear. This approach is used when the patient's hearing is low or when the tumor is large.
MRI image of a patient with bilateral acoustic neuromas (neurofibromatosis type 2). The tumor on the left (the patient’s right) was treated with a translabyrinthine approach.
The surgery is performed with a neurotologist/skull base surgeon and a neurosurgeon in tandem. The surgery is done under general anesthesia. The patients are typically admitted to the hospital for less than a week after surgery.
The most common complications of surgery include facial nerve weakness (temporary or permanent), loss of hearing, dizziness, and leakage of spinal fluid.
It is best that your surgery is done in by both a neurotologist-skull base surgeon (Ear, Nose & Throat subspecialized in ear and skull base surgery) and a neurosurgeon with skull base expertise. The team approach allows the patients to obtain the best care possible.
The surgeons at UC Irvine use endoscopes for the removal of parts of acoustic neuromas in patients. Total endoscopic approach for acoustic neuroma with a very small craniotomy is generally not advised. Occasionally some tumors bleed during removal and the small craniotomy and the totally endoscopic approach does not have enough space for the surgeon to use multiple instruments to control the bleeding. This can lead to severe complications. Other problems that would be encountered in a small craniotomy include bleeding from blood vessels around the tumor which is difficult to control. Finally, the light from the tip of the endoscope creates a great amount of heat. When the endoscope is held very close to the tumor (and its surrounding normal nerves) for the entire duration of the surgery, the risk of heat injury to the nerves is significantly higher. While endsocopes are useful additions to the instruments that surgeons use, its exclusive use for this surgery is generally not advised.
At UC Irvine, our skull base team uses the cutting edge in surgical technique and technology to reduce complications and to improve outcome. Some examples of technology available includes, intra-operative MRI, computer assisted navigation, ultrasonic bone removal, intra-operative multiple cranial nerve monitoring, among others. In addition, the surgeons at UC Irvine routinely use endoscopes in hearing preservation cases to ensure complete tumor removal and to increase the likelihood of hearing preservation. This will also help in reducing brain retraction.
Another area of cutting edge technology available at the UC Irvine Skull Base Program is the use of imaging during the surgery to insure that the entire tumor has been removed. The special intra-operative MRI suite allows the skull base surgeons to obtain an MRI during the surgery to see if the entire tumor has been removed. The patient will generally have an MRI at the beginning of the surgery and one after removal of the tumor. This ensures that the entire tumor was removed. If there appears to be some tumor left, the surgeon will know exactly where it is based on the MRI and can remove it quickly. UC Irvine skull base surgery is one of a few programs in the West Coast to have the capability of intra-operative MRI, which is a must for complex tumors.
Ultrasonic bone removal is a novel device that is used for removal of bone in critical areas around the brain or cranial nerves. Instead of using a high speed drill around the structures of the brain, this device can gently remove bone without the risk to the surrounding structures. The surgeons at UC Irvine use the ultrasonic bone removal system in appropriate cases to reduce injury to the brain, cranial nerves, and the vital structures of the skull base.
Another novel set of instruments used in the removal of skull base tumors is the stimulating dissection instruments. Traditionally, tumors were removed with various instruments and then a stimulator was brought into the field to check for the location of the important nerves in the area. The problem with that system was that the nerves (such as the facial nerve) could be injured while removing the tumor. The stimulating dissection instruments give the surgeon the ability to continually stimulate and look for the nerve as the dissection continues. This allows for maximal preservation of the nerve. The stimulating dissection instruments are used in the removal of all tumors of the posterior and middle skull base at UC Irvine.
Our center has been successful in having superb facial nerve function after removal of large tumors (over 3 cm) by using novel techniques using stimulating dissection instruments, using endoscopes, and occasionally combining surgical resection with post-operative radiosurgery. The use of newer technology allows the surgeons to preserve hearing and facial nerve at a higher rate.
The skull base team at UC Irvine also is one of a handful of teams in the U.S., who in addition to using all 3 surgical approaches, also performs stereotactic radiation (radiosurgery) using both the new Perfection GammaKnife System as well as the CyberKnife System.
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Patients have received care at our center from orange county, california, los angeles, san diego, inland empire, san gabriel valley, san fernando valley, irvine, newport beach, sacramento, fresno, bakersfield