Features of the dynamics of vestibular schwannomas after stereotactic radiosurgery

Background: understanding the patterns of development of post-radiation pseudoprogression is an actual task in the treatment of patients with vestibular schwannomas, since it allows not only to justify the selection of patients for radiosurgical treatment, but also to optimize their subsequent follow-up in order to assess the immediate and long-term results of treatment. Aims: to study for post-radiation dynamics of changes in the volume of vestibular schwannomas depending on the observation time after stereotactic radiosurgery. Material and methods: the study included 541 patients: the ratio of men to women was 1:3, the median follow-up was 55 months. The average age was 48.2 years (18–80). The mean initial volume of vestibular schwannomas was 4.1 cm3 (0.1–14.5). The dynamics of changes were assessed by volumetric comparison on a workstation equipped with Leksell Gamma Plan 10.1 software. An analysis of the dynamics of changes in the volume of schwannomas after radiosurgery was carried out on the basis of the initial tumor volume, the maximum magnitude of the change in volume and the time it was achieved, and the tumor volume at the time of the last observation. Analysis of changes in the volume of schwannomas was carried out at intervals of 12 months after radiosurgery. Results: In 59.7%, vestibular schwannomas progressively decreased after radiosurgery, and post-radiation pseudoprogression occurred in 40.3% of cases. Typical pseudoprogression is characterized by development after irradiation and has either a short course with an early (11.7 months) peak increase in tumor volume and complete reverse development after 24–36 months, or a protracted course with a late (38.1 months) peak (p<0. 0001) and complete reverse development after 60–72 months. Atypical development of pseudoprogression after progressive tumor reduction requires a differential diagnosis with tumor recurrence, which requires a control MRI after 12 months to assess the dynamics of further changes in tumor volume. Re-enlargement of a vestibular schwannoma after previous pseudoprogression most likely corresponds to tumor recurrence. Conclusion: post-radiation pseudoprogression of vestibular schwannomas is a frequent phenomenon with a different course — short and protracted. Monitoring of patients with prolonged pseudoprogression requires MRI for at least 6 years after radiosurgery to reliably assess the treatment outcome. Atypical development of pseudoprogression after progressive reduction requires differential diagnosis with tumor recurrence.