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AJNR - American Journal of Neuroradiology

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American Journal of Neuroradiology 21:1540-1546 (8 2000)
© 2000 American Society of Neuroradiology

ARTICLE

Serial Follow-up MR Imaging after Gamma Knife Radiosurgery for Vestibular Schwannoma

Hiroyuki Nakamura^,a, Hidefumi Jokura^a, Kou Takahashi^a, Nagatoshi Boku^a, Atsuya Akabane^a and Takashi Yoshimoto^a

^a From the Department of Neurosurgery, Tohoku University School of Medicine, Sendai, Japan (H.N., H.J., A.A., T.Y.), and the Department of Neurosurgery, Jiro Suzuki Memorial Gamma House, Furukawa Seiryou Hospital, Furukawa, Japan (K.T., N.B.).

BACKGROUND AND PURPOSE: Gamma knife radiosurgery has become an important treatment option for vestibular schwannoma. The effect of treatment can be assessed only by neuroimaging. We analyzed the evolution of follow-up MR imaging findings after gamma knife radiosurgery to provide information for the clinical management of these tumors.

METHODS: Changes in tumor volume and enhancement were assessed visually on 341 follow-up MR studies obtained in 78 of 86 consecutive patients with unilateral vestibular schwannoma who underwent gamma knife radiosurgery.

RESULTS: Follow-up MR studies were obtained between 10 and 63 months (mean, 34 months) after treatment. Tumor control rate was 81%. Changes in tumor volume were classified as temporary enlargement (41%), no change or sustained regression (34%), alternating enlargement and regression (13%), or continuous enlargement (12%). Temporary enlargement occurred within 2 years after radiosurgery. Changes in tumor enhancement were classified as transient loss of enhancement (84%), continuous increase in enhancement (5%), or no change in enhancement (11%). There was no significant correlation between changes in tumor volume and tumor enhancement. Areas of T2 hyperintensity in adjacent brain tissue appeared in 31% of patients.

CONCLUSION: Dynamic changes in vestibular schwannoma are seen on serial follow-up MR studies obtained after gamma knife radiosurgery. An increase in tumor size up to 2 years after radiosurgery is likely to be followed by regression. Changes in contrast enhancement are not predictive of clinical outcome. Neuroimaging follow-up is recommended.

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