In Reply: Predictors of Hydrocephalus Risk After Stereotactic Radiosurgery for Vestibular Schwannomas: Utility of the Evans Index

To the Editor: We are grateful to Dr Türk and colleagues for their letter1 regarding our manuscript on hydrocephalus after stereotactic radiosurgery for vestibular schwannoma tumors.2 The authors contribute a unique case that parallels our series, albeit in a younger patient without clear ventricular enlargement (Evans Index: 0.25) at the time of stereotactic radiosurgery. The authors raise several pertinent questions related to follow-up and treatment strategies. The first is the issue of time—when do tumors typically regress and is this timeline altered in a patient who developed hydrocephalus? Naturally, tumors may transiently expand in the first phase after radiosurgery, thought to be inflammatory-mediated as part of the cellular and vascular response.3,4 Second, after a few years, many tumors show regression, and this is no exception for patients who developed hydrocephalus and were shunted.5 In the series from Lee et al,6 all patients who underwent cerebrospinal fluid diversion had tumor regression and complete local control. Despite these promising results, it still remains unclear if addressing the hydrocephalus affects tumor regression. Our data highlighted that not all cases of hydrocephalus occur after tumor expansion.2 Given this, after the development of increasing ventriculomegaly, we recommend starting with routine imaging every 6 months with intervals depending on clinical and imaging findings. Regarding management options, both cerebrospinal fluid diversion and surgical resection are reasonable to treat hydrocephalus, and shared decision making with each patient is paramount.7,8 Of course, surgical resection may be better reserved for larger tumors with mass effect precipitating brainstem dysfunction.