Navigating change and the acoustic neuroma story: methods, outcomes, and myths.

Acoustic neuromas (vestibular schwannomas) are generally slow-growing, intracranial extra-axial benign tumors that usually develop from the vestibular portion of the eighth nerve. Unilateral vestibular schwannomas account for approximately 8% of all intracranial tumors; one of every 100,000 individuals per year develops a vestibular schwannoma.103 Bilateral vestibular schwannomas are usually associated with neurofibromatosis 2 (NF2). Both unilateral and bilateral vestibular schwannomas may form as a result of malfunction of a gene on chromosome 22, which produces a protein, Merlin, that controls the growth of Schwann cells. In patients with NF2, the faulty gene on chromosome 22 is inherited and is present in all or most somatic cells. However, in individuals with unilateral vestibular schwannoma, for unknown reasons, this gene loses its ability to function properly and is present only in the schwannoma cells.49 A progressive decline in unilateral hearing is the most common symptom that leads to the diagnosis of a vestibular schwannomas.44 Only 3 to 5% of patients with vestibular schwannoma have normal hearing at the time of diagnosis. Overall, three separate growth patterns can be distinguished: 1) no or very slow growth; 2) slow growth (i.e., 0.2 cm/yr linear growth on imaging studies); and 3) fast growth (i.e., 1.0 cm/yr). Although most vestibular schwannomas grow slowly, some grow quite quickly and can double in volume within 6 months to 1 year.8 A small number of tumors appear to alternate between periods of no or slow growth and rapid growth. Cystic vestibular schwannomas are sometimes capable of relatively rapid enlargement of their cystic component. Spontaneous intratumoral hemorrhage has been rarely described but has occurred mainly in cases of large multicystic tumors.99 Using high-resolution scans such as magnetic resonance imaging (MRI), these tumors can be distinguished easily. With the addition of stereotactic radiosurgery, management options have expanded for many patients. Management Methods and Outcomes Early diagnosis of a vestibular schwannoma is key to preventing its serious consequences. There are three primary options for managing a vestibular schwannoma: 1) surgical removal; 2) radiosurgery; and 3) observation with serial imaging studies. In addition, some centers suggest conformal fractionated radiation therapy using linear accelerators or proton beam radiation.