Intraoperative MRI and adjuvant radiosurgery

For many patients with brain tumors, the ideal management strategy may be a planned subtotal resection followed by stereotactic radiosurgery (SRS). However, intraoperative visual inspection may be an inadequate measure of the amount of residual lesion. Intraoperative MRI (IMRI) may help to ensure that the goals of surgery have been achieved and that the best possible target for SRS remains.

We have operated on 68 patients using the PoleStar N-10 IMRI system (Odin Medical Technologies, Yokne'am, Israel). Benign extraaxial lesions were present in 34 patients. In 12 patients subtotal resection and adjuvant SRS were planned. Diagnoses included 5 pituitary adenomas, 4 meningiomas, 2 vestibular schwannomas, and 1 trigeminal schwannoma. Tumor resection was performed until critical structures (e.g. superior sagittal sinus) were being approached and IMRI demonstrated that the lesion was as small as possible.

In 1 patient a surgical resection was completed, while in 11 others the plan for subtotal resection was carried out. One patient with an extensive meningioma was treated with fractionated 3-dimensional conformal fractionated radiation therapy, as her tumor remained too large for SRS. In the remaining 10 patients an ideally small target remained for SRS; 3 patients have been treated so far.

Adjuvant SRS after subtotal tumor resection is an excellent management strategy for many patients with intracranial tumors. IMRI can ensure that the surgical goals have been reached. Future comparison of target volumes, integral volume doses, and patient outcomes are planned.