The consensus conferences panel of experts reported: "Currently, the ideal treatment for symptomatic patients with vestibular schwannoma is the total excision of the tumor in a single stage with minimal morbidity and mortality and with preservation of neurological function." Total surgical removal was not, however, the only treatment indicated at the time. Partial removals were in use to debulk very large VSs threatening to compress vital structures. And long-term observation management was deemed appropriate as MRI scans began to reveal more and more small tumors with stable neurological symptoms. Radiosurgery
By the 1980s, radiation therapy was also becoming an attractive option for VS patients. At the Karolinska Institute in Stockholm, Sweden, Lars Leksell (1907–1986) pioneered Gamma Knife radiosurgery. In 1951, he published his landmark scientific paper, "The Stereotaxic Method and Radiosurgery of the Brain," defining radiosurgery as "the destruction of intracranial targets without opening the skull using very high doses of ionizing radiation in stereotactically directed beams." The first Gamma Knife machine was operable in Sweden in 1969, and the first Gamma Knife in the U.S. was installed in 1987 at the Presbyterian University Hospital in Pittsburgh, PA. Departments of radiation oncology at major medical centers began to modify X-ray linear accelerators (linacs) to do single-session radiosurgery and multiple-session radiotherapy. In 1991, the U.S. National Institutes of Health convened a Consensus Development Conference (December 11–13, 1991) for Acoustic Neuroma (Vestibular Schwannoma) to evaluate management of the disorder and recommend areas for future activity and research."
Radiation dosages overall were reduced over the years as experience showed that excellent tumor control rates could be maintained even as dosages were lowered to benefit hearing preservation and facial nerve function. Generally, single-session Gamma Knife radiosurgery is limited in use to VSs less than 3 cm in diameter to avoid possible complications with facial nerves, brainstem and the cochlea apparatus. The risk of radiation-induced secondary tumors is very small, in the range of 0.01-0.02%. The risk for NF2 patients appears to be slightly higher. Medical and gene therapies
The 1991 NIH Consensus Statement recommended attention to "the development of pharmaceutical and other alternative medical treatments, such as tumor suppressing agents." Ideally, a drug could be found to permanently shrink or eradicate VSs, with minimal side effects. A key step forward in 1993 was the identification of the NF2 gene and its protein product Merlin, which modulates the complex molecular signaling pathways that control cell proliferation. These pathways that drive VS formation (tumorigenesis) and growth are currently under investigation. A second important field of study in molecular biology investigates ways to stop the formation (angiogenesis) of the new blood vessels that are needed to support tumor growth by supplying nutrients and oxygen. In 1998, the glycoprotein named VEGF (vascular endothelial growth factor) that initiates proliferation was discovered. An anti-VEGF drug named bevacizumab (Avastin) was developed and showed promise in stopping this vascular proliferation. Unfortunately, when tested for NF2 tumors, the therapy required prolonged treatment resulting in hypertension and impaired wound healing.