Stereotactic Radiosurgery Superior to Observation for Koos Grade I Vestibular Schwannomas

A recent international study has demonstrated that stereotactic radiosurgery (SRS) is more effective than observation for controlling tumor progression and preserving neurological function in patients with Koos grade I vestibular schwannomas. Published in Neurosurgery, the findings challenge the traditional approach of managing smaller, asymptomatic tumors with observation alone.

SRS Provides Consistent Tumor Control Over Time

The VISAS-K1 study, led by Dr. Jason P. Sheehan of the University of Virginia Medical Center, analyzed data from 261 patients with Koos grade I vestibular schwannomas. Of these, 182 underwent SRS using the Gamma Knife system, while 79 were managed with observation. Tumor control was defined as stability or regression of the vestibular schwannoma from baseline measurements.

The study found that tumor control rates were consistently higher in the SRS group, reaching 99% at three, five, and eight years, with only one case of tumor progression. In contrast, control rates for the observation group declined over time: 63% at three years, 50% at five years, and 33% at eight years. These findings were confirmed in a matched cohort analysis of 71 SRS patients and 71 observed patients. In this subgroup, SRS achieved 100% tumor control at all time points, compared to significantly lower rates of control in the observation group (63.5% at three years, 49% at five years, and 29.5% at eight years).

Neurological Benefits Highlight SRS Advantages

Beyond tumor control, SRS demonstrated significant advantages in preventing neurological impairment. Compared to observation, SRS was associated with a 54% lower incidence of tinnitus, an 83% lower incidence of vestibular dysfunction, and a 51% lower incidence of cranial nerve deterioration in the unmatched cohort. In the matched cohort, SRS was linked to a 74% lower risk of cranial nerve deterioration. The study also highlighted that neurological dysfunctions occurring during observation may not be reversible, even if SRS is administered later.

Interestingly, hearing preservation rates were similar between the two groups. Both underwent audiometric assessments, and no significant differences in serviceable hearing preservation were observed at three, five, or eight years.

Why It Matters

These findings suggest a potential shift in the management of small, asymptomatic vestibular schwannomas. Historically, these tumors have been managed conservatively with observation, reserving treatment for larger or symptomatic cases. However, the data indicate that early intervention with SRS could provide superior long-term tumor control and reduce the risk of irreversible neurological impairment.

As Dr. Sheehan and colleagues state, “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.” The study underscores the importance of balancing conservative management against the benefits of early SRS treatment in appropriate patients.

With its proven efficacy in tumor control and its role in mitigating neurological dysfunction, SRS may increasingly influence treatment protocols for patients with Koos grade I vestibular schwannomas, particularly as clinicians strive to prevent long-term complications.