Peritumoral Hyperintense Signal on Post-contrast FLAIR Images Surrounding Vestibular Schwannomas Following Stereotactic Radiosurgery

BACKGROUND AND PURPOSE: Prior investigations have noted the presence of peritumoral hyperintense signal (a “halo”) around vestibular schwannomas on postcontrast 3D T2 FLAIR images. This study evaluated this phenomenon in a cohort of patients undergoing stereotactic radiosurgery.

MATERIALS AND METHODS: A retrospective review was completed of consecutive patients with presumed vestibular schwannomas undergoing stereotactic radiosurgery. Tumor size, location, presence or absence of a peritumoral halo, and halo thickness were recorded. Images were reviewed for presence and size of peritumoral hyperintense signal on postcontrast 3D T2 FLAIR images before and after treatment.

RESULTS: Twenty-six patients were included in this study, 14 of which were female (54.0%). Average age was 62±12 years. Prior to treatment, a post-contrast 3D T2 FLAIR hyperintense peritumoral halo was seen in 85% of patients, averaging 0.8±0.4 mm in thickness. There was a higher incidence of peritumoral halo in post treatment patients (96%) than pre-treatment patients (85%) (p=0.017) with a mean follow up period of 1.2 years (SD, 0.35) from 11/12/2019 to 9/5/2023. The average halo thickness was also larger in posttreatment patients (average=1.4±0.4 mm) compared to pre-treatment patients (0.8±0.4 mm) (p<0.001). Average tumoral size did not significantly change following treatment (p=0.10).

CONCLUSIONS: Vestibular schwannomas treated with stereotactic radiosurgery are more likely to have a peritumoral halo on post-contrast 3D T2 FLAIR images, with larger halo size as compared to pre-treatment studies. Further study with a larger tumor cohort and longer follow-up will be necessary to determine if these findings are predictive of subsequent tumor shrinkage.

ABBREVIATIONS: VSs = vestibular schwannomas; SRS = stereotactic radiosurgery; CPA = cerebellopontine angle; IAC = internal auditory canal.