In Reply: Scoring System Assessing Risks of Growth in Sporadic Vestibular Schwannoma

To the Editor: I appreciate the thoughtful critique of our work and would like to address several key points raised.1,2 We fully acknowledge the absence of functional outcome data in the previous study. This initial work was intended as a focused radiologic perspective, a foundation for broader, integrative models. We have been collecting audiovestibular, facial nerve function and patient-reported functional data along with radiomics features as part of an ongoing poly-omics model, which will be the subject of a forthcoming publication. Unfortunately, regarding quality of life, our center does not maintain systematic retrospective data, and we recognize this as a limitation of the current data set. Regarding the 10% annual growth threshold, our intention was to highlight the importance of 3-dimensional volumetric assessment over linear (arithmetic) diameter measurements, which often underestimate true tumor progression. Advances in automated segmentation tools and volumetric calculation software have significantly improved measurement sensitivity and reduced the likelihood of human error. We view the 10% threshold not as a rigid clinical trigger but rather as a protective early warning marker, designed to flag subtle but potentially meaningful changes that could precede more rapid clinical deterioration if left unmonitored. It is a conservative threshold that supports vigilance in long-term surveillance, particularly in younger or high-risk patients. On the issue of attrition bias, we agree entirely. The discharge of patients after 5-10 years of stable imaging was standard practice during an earlier period in our institution, before the now widely recognized risk of delayed tumor growth. We acknowledge that this may have introduced bias and are re-evaluating our surveillance protocols accordingly. Regarding cystic morphology, the underlying pathophysiology remains largely unknown and is likely multifactorial, involving processes such as inflammatory changes and intratumoral hemorrhage. In our study, we grouped primary and secondary cystic vestibular schwannomas for the necessary simplification, as it is not currently possible to determine the precise biological mechanism behind cystic transformation from simple MRI. Furthermore, our observations suggest that vestibular schwannomas initially present as homogeneous lesions. To date, we have not identified cystic vestibular schwannomas at earliest stage (2-3 mm, Koos grade I), regardless of whether they were detected incidentally or symptomatically. This finding implies that cystic transformation is a secondary phenomenon occurring during tumor's natural history and positions us only as observers of this process at different timeframes of its evolution. Finally, with respect to external validation, we fully agree with its necessity. We are currently engaged in a collaboration with another center to externally validate and refine our model using an independent data set. We appreciate the opportunity to respond and welcome the ongoing dialogue.