Stereotactic Radiosurgery Achieves High Rates of Tumor Control for Koos Grade

As primary care for Koos grade I vestibular schwannomas, stereotactic radiosurgery (SRS) is superior to observation with regard to tumor control and preservation of neurologic function, according to the results of an international, multicenter retrospective study.

Jason P. Sheehan, MD, Ph.D., a neurosurgeon at the University of Virginia Medical Center, and colleagues report the details in "Vestibular Schwannoma Koos Grade I International Study of Active Surveillance Versus Stereotactic Radiosurgery: The VISAS-K1 Study." The article published online ahead of print on November 6, 2024 and is expected to appear in the January issue of Neurosurgery.

"Our strategy for managing patients with Koos grade I vestibular schwannomas has traditionally involved treating larger tumors and those causing symptoms with SRS, while smaller, asymptomatic tumors were observed," Dr. Sheehan's group reports. "However, the findings from this study, along with other published studies, indicate that even asymptomatic patients with smaller tumors may benefit from SRS over observation at the time of diagnosis."

SRS was consistently associated with significantly better tumor control over 8 years

The team gathered data compiled by the International Radiosurgery Research Foundation on 261 adults with Koos grade 1 vestibular schwannomas: 182 who underwent SRS and 79 who were observed. In all cases of SRS, the procedure was performed in a single session using the Gamma Knife system, leveraging contrast-enhanced MRI or CT scans for precision targeting. All patients were followed for at least six months after surgery (or after diagnosis, in the observation group).

Tumor control, defined as stability (<25% change) or regression of the vestibular schwannoma from baseline, was noted in 99% of the SRS group at three years, five years, and eight years. There was only one event of tumor progression. By comparison, the tumor control rate in the observation group was 63% at three years, 50% at five years, and 33% at eight years.

The researchers also compared subgroups of 71 SRS-treated patients and 71 patients who underwent observation, matched on age, sex, tumor volume, pure tone average, and speech discrimination scores. In those analyses, too, tumor control was significantly superior with SRS compared with observation. The SRS group exhibited 100% control at all time points studied, whereas tumor control rate in the observation group was 63.5% at three years, 49% at five years, and 29.5% at eight years.

Rates of hearing preservation did not differ significantly between groups. Patients underwent serial audiometric assessments and had their hearing classified into four levels (American Academy of Otolaryngology–Head and Neck Surgery classes A, B, C, and D), where classes A and B were defined as serviceable hearing. There was no significant difference between the SHS and observation groups in rates of serviceable hearing preservation at three, five, or eight years, in either the unmatched or matched cohorts.

SRS significantly reduced neurological impairment compared with observation

In the unmatched cohorts, SRS was associated with a 54% lower incidence of tinnitus relative to observation, an 83% lower incidence of vestibular dysfunction, and a 51% lower incidence of cranial nerve deterioration. All of these differences were statistically significant. A significantly lower risk of cranial nerve deterioration, by 74%, was also noted in the matched cohort analysis.

"Crucially, the onset of neurological dysfunctions under observation may not be reversible with subsequent SRS," Dr. Sheehan and his co-authors remind clinicians, including neurosurgeons and otolaryngologists who frequently manage such patients.

"Hence, while conservative management is a valid approach for Koos I vestibular schwannomas, necessitating action upon clinical or radiological progression, it is imperative to acknowledge that established neurological symptoms at the time of treatment might persist despite tumor control through SRS."

The research team concludes, "These results suggest a potential shift in our management algorithm, where earlier intervention with SRS could be considered for a broader range of patients, including those with smaller, asymptomatic tumors, to achieve better long-term tumor control and possibly prevent the progression of symptoms."