As microsurgical resection after failed radiosurgery is associated with higher morbidity in patients with vestibular schwannoma (VS), the identification of factors that may influence radioresistance plays a critical role. Additionally, differentiating between treatment-related changes (pseudoprogression) and tumor relapse (TR) can often be challenging. This study aims to identify radioresistance predicting factors and, secondly, to differentiate pseudoprogression from TR at an early stage.
A cohort of 705 patients with unilateral sporadic vestibular schwannoma who underwent stereotactic radiosurgery (SRS) at the same center from 1998 to 2020 was retrospectively analyzed. Clinical data concerning symptoms, tumor volume (Hannover and OHATA Classification), side effects of SRS were recorded. Of these patients, 598 achieved remission while 107 experienced TR and required a second treatment, either microsurgical resection or SRS.
In our cohort, TR was significantly higher in women (p<0.05). However, clinical symptoms such as facial palsy, hypoacusis, tinnitus, and vertigo, as well as tumor volume and tumor configuration (cystic vs solid), were not predictive factors for radioresistance. Patients who experienced TR had significantly more side effects of SRS (20.6% vs 8.4%, p<0.001), particularly regarding facial spasm (p<0.001). A higher risk of facial spasm was significantly related to OHATA-Class (A>B>C>D). An earlier recurrence was observed in cystic tumors. The average follow-up period was 4 years for the recurrence group and 7 years and 10 months for the remission group. Regarding the trend of relative and absolute tumor volumes, a significant difference (p<0.001) was observed between patients with and without TR. This became noticeable at 12 months and even more evident at 24 months after SRS. In this time frame, patients without TR had a decrease in volume, while patients with TR showed an increase.
Clinical symptoms, tumor volume, and tumor configuration are not predictive factors of TR. Only female sex predisposes to an increased risk of TR. Patients with TR experience significantly higher side effects of SRS, particularly facial spasm. TR is strongly suspected at 12 months and even more at 24 months after SRS if there is a further increase in absolute and relative tumor volume, making pseudoprogression unlikely.