Acoustic neuromas (vestibular schwannomas) are slowly growing benign tumors of the eighth cranial nerve arising in the internal auditory canal and cerebellopontine angle. These tumors are relatively rare in the general population with an incidence of 1 per 100,000. They are much more frequent in patients with neurofibromatosis type 2. The average age of diagnosis of acoustic neuromas is 45 years, but they can develop at almost any age.
Early signs and symptoms include gradual ipsilateral hearing loss, tinnitus, and dizziness or vertigo. Advanced tumors in the cerebellopontine angle may produce other symptoms due to mass effect. The various treatment options include initial observation, surgery, fractionated external beam radiation therapy, or Gamma Knife radiosurgery.
Gamma Knife radiosurgery is an established outpatient treatment for these tumors with tumor control rates exceeding 95%. Moreover, the usual risks of an open operation such as bleeding, infection, cerebrospinal fluid leak, general anesthesia, etc can be avoided.
Although most patients have preservation of hearing, a significant number of patients have continued worsening of hearing after radiosurgery with the Gamma Knife.
An open procedure using microsurgical techniques to resect the tumor is another effective treatment for these tumors. Optimal surgical candidates are those with larger tumors, or very young patients.
Fractionated external beam radiation therapy is another treatment option. Patients who are poor operative risks and have tumors too large for Gamma Knife radiosurgery would best be treated with external beam radiation therapy.
Since these tumors can be slowly growing, some older patients with multiple medical problems and small acoustic neuromas can be initially observed. In these cases, treatment is reserved for those tumors with either demonstrated radiographic progression or worsening ipsilateral hearing.
Complications and Outcomes
There are very few short-term risks with the Gamma Knife. Over many months after Gamma Knife radiosurgery there is a low risk of complications including radiation damage to other nearby cranial nerves (facial and trigeminal nerves), or adjacent normal brain. In addition, hearing may worsen after treatment with Gamma Knife. These risks have been reduced by using lower radiation doses.
Flickinger JC, et al. Int J Radiat Oncol Biol Phys, 60:225, 2004
Mendenhall WM, et al. Am J Otolaryngoloty, 25:38, 2004