General Philosophy

With the advent of specialized techniques in microsurgery, neuro-anesthesiology, and intraoperative monitoring, the safety and effectiveness of surgery for acoustic neuromas has considerably improved over the past 10 years.

In addition to surgical treatment, therapy using stereotactic radiosurgery and nonsurgical monitoring of small tumors has provided new options in the treatment of these lesions. The guiding philosophy at UW Medicine is to manage patients with acoustic neuromas without producing any new neurologic deficits. In some cases, this leads to early surgery to preserve hearing, and in other cases this means observing the tumors over time if surgery is felt to be more risky. The most important feature of this approach is the patient: treatment is individualized depending on the unique circumstances for each patient to assure the best outcome.

Pre-Operative Testing

Each patient undergoes a multidisciplinary pre-operative evaluation prior to acoustic neuroma treatment. In addition to the usual preoperative tests (electrocardiogram, blood tests, chest x-ray, etc.) the patient has the following studies:

Audiogram: This measures the hearing capacity for both the affected and opposite ears. This information guides the team in decisions about when to operate and whether hearing can be preserved.

Brainstem Auditory Evoked Potential: This test measures the conduction of electrical signals along the cochlear (hearing) nerve. This preoperative assessment is essential when hearing is present since this test is used during surgery to monitor the cochlear nerve in order to preserve hearing.

Vestibular Testing: Vestibular (balance) testing is done to determine the amount of loss of balance function of the inner ear from the tumor and which branch of the balance nerve is affected. Some patients have little loss of function and can expect to be quite dizzy after surgery. Others have already lost their balance function and have little difficulty.

The main vestibular test is the ENG (electronystagmogram), which measures the function of the respective inner ear balance organs Balance function is also measured with a posturography platform test. Not all patients undergo vestibular testing preoperatively. The test may help identify those patients who will require more aggressive vestibular rehabilitation therapy postoperatively.

At UW Medicine, our neurosurgeons use three different surgical approaches to treat skull base tumors. Each has advantages and disadvantages and is individualized on the basis of hearing level, size and location of the tumor and patient wishes.

Suboccipital Approach
 
In this approach a window of bone is removed from the skull behind the mastoid. Upon closure this bone is re-placed. Gentle retraction of the cerebellum provides exposure of the tumor at the brain stem. Additional bone is removed overlying the posterior part of the internal auditory canal. This approach provides excellent exposure of the tumor and adjacent brain tissue and allows for hearing preservation. It may be used for small and large tumors. In a retrospective review of nearly 100 patients at the UWMC hearing was preserved in almost 70% of patients when the tumor size was less than 2 cm. The total length of the operation varies from 6-12 hours, depending upon the size of the tumor and whether it is adherent to critical structures.

Translabyrinthine Approach

The translabyrinthine approach was developed in the 1960s for use in patients with small- to medium-sized tumors in whom hearing function was absent or non-useful. At that time, this approach was a great technical advance and it substantially reduced the complication rate after surgery. There are three technical advantages to the translabyrinthine approach: exposure, bone removal, and identification of the facial nerve. By directing the surgical access through the mastoid bone and inner ear (labyrinth) there is less need for retraction of the brain for exposure. In addition, the bone dust from drilling is removed before the membrane surrounding the brain is opened, which decreases the amount of headache after surgery. Finally, the facial nerve is identified early in the case, which reduces the chance of injury. The principal disadvantage of this technique is total deafness.

Middle Fossa Approach

In this approach a window of bone is removed from the skull above the ear. The brain is gently lifted from the skull base and the bone overlying the tumor in the internal auditory canal is removed from above. This approach is best suited for small tumors in ears with good hearing. When favorable preoperative conditions exist hearing preservation rates may approach 80%. The major disadvantage is a higher incidence of temporary facial weakness.

Stereotactic Radiosurgery

This is an outpatient, nonsurgical procedure in which a beam of high-dose radiation is focused on the tumor. The radiation may be delivered in a single dose or multiple (fractionated) doses. This delivery is intended to minimize injury to the surrounding nerves and brain tissue. Tumor growth ceases in over 90% of patients and rarely the tumor may shrink. Initial hearing preservation rates have been high but decline over time.