Acoustic neuroma surgery

Overview
Because these neuromata grow so slowly, a physician may opt for conservative treatment beginning with an observation period. In such a case, the tumor is monitored by annual MRI to monitor growth. Records suggest that about 45% of acoustic neuromata do not grow detectably over the 3-5 years of observation. In rare cases, acoustical neuromata have been known to shrink spontaneously. Often people with acoustic neuromata die of other causes before the neuroma becomes life-threatening. (This is especially true of elderly people possessing a small neuroma.)

Since the growth rate of an acoustic neuroma rarely accelerates, annual observation is sufficient. Acoustic neuromata may cause either gradual or&mdash;less commonly&mdash;sudden hearing loss and tinnitus.

Surgery
Removal of acoustic neuromas may be performed using several approaches. Each approach has its advantages and disadvantages. Microsurgery for acoustic neuroma is the only technique that removes the tumor. Radiation treatment (discussed in another section) does not remove the tumor, but has the potential to slow or stop its growth. Surgery is the only treatment that will definitively treat balance symptoms associated with tumor growth, as the vestibular nerves are removed at surgery.

Choice of surgical approach is based on the patient's age, medical condition, size of tumor, and preoperative hearing thresholds and speech discrimination, as well as other tests such as electronystagmography, imaging, and auditory brainstem response testing. With large tumors, the patient is usually deaf at presentation. Surgery is still indicated to prevent further compression of posterior fossa structures. The patient's and surgeon's preferences also play a significant role.

During removal of the tumor, the tumor along with the superior and inferior vestibular nerves are removed. This results in an acute loss of vestibular input to the brain from the operated side. However, vestibular function improves rapidly due to compensation by the other ear and other balance mechanisms.

Surgery carries risk to the facial nerve which is therefore monitored during the procedure. Best results (normal or near normal facial function) are more likely with small acoustic neuromas.

Three surgical approaches are commonly used. The first is the translabyrinthine approach, which destroys hearing in the affected ear. Thus, it is often employed in patients who have poor speech discrimination in the affected ear. Any size tumor may be removed with this approach. There is no brain retraction with this approach, so it is often considered the safest route to remove the tumor. In patients with neurofibromatosis type 2 who undergo auditory brainstem implantation, this technique is used as it provides the most direct path of access to the lateral recess and cochlear nucleus, where the device is placed.

The two other approaches (suboccipital retrosigmoid and middle fossa) are hearing preservation approaches, which have a chance of preserving some or all of the hearing in the affected ear. Neurosurgeons often prefer the retrosigmoid approach, as they are frequently more familiar with it from training.

The middle fossa approach is used for tumors typically less than 2cm in greatest dimension, where hearing conservation is to be attempted. This approach has the advantage over the retrosigmoid approach in its direct access to the lateral end of the internal auditory canal. Multiple reports have shown that the retrosigmoid approach cannot reach the lateral end of the internal auditory canal without violating the posterior semicircular canal, and hence destroying the hearing.

A less common approach is minimally invasive endoscopic surgery. This approach is available in specialized centers. This technique is not widely used due to concerns over bleeding and the inability to remove tumors from the internal auditory canal with this method.

Acoustic neuroma surgery is highly technically demanding, and patients are advised to seek out surgical teams with extensive experience.