Stereotactic radiosurgery of vestibular schwannoma is an effective and safe method of treatment. The phenomenon of schwannoma pseudo-progression (transient post-radiation enlargement) complicates assessment of the outcomes after radiosurgery.

OBJECTIVE

To investigate the changes of vestibular schwannoma in different periods after radiosurgery.

MATERIAL AND METHODS

We analyzed early and long-term radiation-induced changes in 333 patients who received Gamma Knife treatment at the Burdenko Neurosurgery Center between April 2005 and December 2015. Mean follow-up period was 60 months (range 15—167). There were 89 men (26.7%) and 244 (73.4%) women. Mean age of patients was 48.2 years. Mean baseline tumor volume was 4.1 cm³ (range 0.1—14.5). Dynamics of changes was assessed using volumetric comparison.

RESULTS

Tumor shrinkage without pseudo-progression was observed in 149 (44.7%) patients. Typical pseudo-progression in different variants was found in 131 (39.3%) patients, i.e. short-term (1 year) and long-term (≥2 years) course, complete and incomplete process. Eleven patients had atypical pseudo-progression after initial tumor shrinkage. Progression-free 5- and 10-year survival in the entire group was 87 and 81%, respectively. Progression-free 5-year survival rate was 95 and 92% in patients with and without pseudo-progression, respectively. Ten-year survival rate was 89 and 89%, respectively.

CONCLUSION

Knowledge of pseudo-progression features is essential for the most reasonable and reliable assessment of treatment results and justification of timing and frequency of subsequent MR control. Atypical course of pseudo-progression can simulate tumor recurrence. In case of tumor enlargement at any follow-up stage after radiosurgery, advisability of surgery should be determined considering clinical data and likelihood of tumor shrinkage following natural regression of post-radiation tumor enlargement.