Long-term tumour control of cystic and solid vestibular schwannoma treated with LINAC-based stereotactic radiosurgery: a retrospective analysis.

Purpose: The implications of intratumoural cystic change on management and treatment outcomes in vestibular schwannoma (VS) remain uncertain. This retrospective analysis aims to compare the treatment outcomes of solid and cystic tumours treated with linear accelerator (LINAC)-based stereotactic radiosurgery (SRS).

Methods: Sixty-eight patients were analysed including 22 with cystic tumours. All received a marginal dose of 12 Gy to the 80% isodose line (range: 70-90%) delivered in a single fraction. Local progression was defined as a maximum linear dimension (MLD) enlargement of > 2 mm persisting for over 2 years, pseudoprogression as an MLD enlargement of > 2 mm within the first 2 years followed by stability or reduction.

Results: With an average follow-up of 92.2 months, crude tumour control rates were similar: 95.5% for cystic and 93.5% for solid tumours. Pseudoprogression occurred in 7 patients (10.3%), 2 with solid (4.3%) and 5 with cystic VS (22.7%). The mean MLD reduction was 4.2 mm for solid tumours and 5.0 mm for cystic tumours (p = 0.51). Only pretreatment size correlated with the percentage reduction in tumour diameter (p = 0.025). Although a higher proportion of cystic tumours demonstrated at least a 10%, 20%, and 30% size reduction compared to solid tumours, none of these differences were statistically significant.

Conclusion: LINAC-based SRS achieves similar tumour control for both cystic and solid VS. Despite cystic tumours being typically of higher Koos grade, they may demonstrate numerically greater reduction after SRS. Future studies should aim to standardise the criteria for classifying cystic tumours.