Acoustic Neuroma

Difficulty with hearing and balance is sometimes caused by a non-cancerous tumor known as an acoustic neuroma (vestibular schwannoma). It’s the type of tumor that typically grows very slowly or not at all. Yet it may still place pressure on the eighth cranial nerve (vestibulocochlear nerve) connecting the brain to the inner ear. Treatment for acoustic neuromas may involve:

• Regular observation
• Radiation
• Surgery

Some growths can be sporadic in nature. Others are related to neurofibromatosis type II (NF2), a disorder where noncancerous tumors develop within the nervous system. NF2 is rare and only accounts for about five percent of all acoustic neuromas. Most growths are the sporadic form. The cause of sporadic abnormal vestibulocochlear nerve formations isn’t known. The only identified risk factor is exposure to large amounts of radiation in the head and neck area.

Early symptoms may be subtle and are sometimes assumed to be age-related hearing loss, since this is the most common symptom associated with the condition. If nerves are not being compressed, there may be no symptoms experienced. When hearing loss is experienced because of an acoustic neuroma, it’s usually gradual and asymmetric (present in one ear only). Hearing loss may be accompanied by tinnitus (persistent sound/ringing in the ear). In some people, symptoms will progress rapidly, although gradual progression is more common. Additional symptoms associated with acoustic neuromas may include:

• Feeling of “fullness” in the affected ear
• Dizziness or vertigo
• Difficulty with balance
• Facial weakness or numbness
• Hoarseness and difficulty swallowing
• Unsteadiness
• Taste changes

Severe symptoms that include mental confusion should be treated right away. This is usually a sign that nerve compression is affecting certain parts of the brain.

Diagnosing an acoustic neuroma often involves ruling out other possible causes. Image tests such as an MRI scan can determine whether or not there is a growth affecting the vestibulocochlear nerve. A patient’s medical history and the specific symptoms experienced will be taken into account when diagnosing an acoustic neuroma. If hearing loss is the only symptom, patients may be referred to an ear, nose, and throat specialist.

Sometimes referred to as “watchful waiting,” observation is a common treatment recommendation for patients with acoustic neuromas. Patients over 60 with small tumors (less than 2 cm or those with multiple medical problems are the patients who are usually observed. The patients who elect to have watchful-waiting need MRI 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.

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 90-95% of tumors. The most common side effects of radiation include facial numbness, deafness, among others. Facial paralysis occurs ~1% of time. At least half of the patients whose tumors grow after radiation will need surgery. Those patients who need surgery after radiation generally have poorer facial nerve function because radiation leads to scarring of the tumor. The long-term (>25 years) consequences of stereotactic radiation to acoustic neuromas are not known.

Hearing Preservation Approaches:

Middle Fossa Approach

The middle fossa approach is used for small tumors under 15 mm (3/5th of an inch) in patients who have useful hearing. The approach involves an incision in front of the ear in the hairline and removal of the tumor from above. Hearing is preserved in 60-80% of patients depending on the size of the tumor and baseline hearing. Using endoscopes for tumor removal can increase the likelihood of preserving hearing.

The middle fossa approach has the disadvantage that requires brain retraction. The temporal lobe of the brain is retracted during the surgery and studies have shown permanent EEG changes in the brain after the middle fossa approach. Additionally, the risk of temporal lobe seizures increases with this approach. Finally, right handed patients with left sided tumor (language portion of brain is on the left) are at risk of having some issues with language post-surgery. Due to the above problems, our preference is to use the endoscopic-assisted retrosigmoid approach for small tumors which does not require temporal lobe retraction. We reserve the middle fossa approach for patients with facial neuromas or other middle fossa lesions that cannot be approached through the retrosigmoid approach.

Retrosigmoid Approach

The retrosigmoid approach (sometimes called the suboccipital approach by neurosurgeons) 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 50-80% of cases depending on the size of the tumor and baseline hearing. In general, the better the hearing is before surgery, the higher chance of preservation. Endoscopes can be used to remove tumors to increase the likelihood of preserving hearing.

Hearing Sacrifice Approach:

Translabyrinthine Approach

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.

What does surgery involve? 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. The average duration of hospitalization is 3 to 5 days. The younger and healthier (general health) patients tend to leave after 3 days and older patients take longer in the hospital before their balance is stronger.

What are the complications of surgery? The most common complications of surgery include facial nerve weakness (temporary or permanent), loss of hearing, dizziness, and leakage of spinal fluid. The rates of these complications vary depending on the size of the tumor, baseline hearing function, anatomy of the temporal bone, among others. In a landmark study performed by our team we have found that patients who get surgery at a high volume acoustic neuroma center have lower complications, shorter hospital stay, and lower cost.

What to look for in your surgeon? 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, computer assisted navigation, ultrasonic bone removal, intra-operative hearing and multiple cranial nerve monitoring, among others. In addition, the surgeons at UC Irvine routinely use endoscopes in all cases, especially 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. We also place top priority on facial nerve preservation to ensure the patient has the best possible facial nerve function after surgery.