Peritumoral Hyperintense Signal on Postcontrast 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 whom were women (54.0%). Average age was 62 ± 12 years. Before treatment, a postcontrast 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 posttreatment patients (96%) than pretreatment patients (85%) (P = .017) with a mean follow-up period of 1.2 years (SD 0.35) from November 12, 2019, to September 5, 2023. The average halo thickness was also larger in posttreatment patients (average =1.4 ± 0.4 mm) compared with pretreatment patients (0.8 ± 0.4 mm) (P < .001). Average tumoral size did not significantly change following treatment (P = .10).

CONCLUSIONS: Vestibular schwannomas treated with stereotactic radiosurgery are more likely to have a peritumoral halo on postcontrast 3D T2 FLAIR images, with larger halo size as compared with pretreatment 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.