RADIOSURGERY FOR VASCULAR MALFORMATIONS OF THE BRAIN-STEM

The challenges associated with microsurgery of vascular malformations located in the midbrain, pons and medulla have promoted the developmen t of alternative therapeutic techniques. To assess the efficacy and sa fety of radiosurgery in the management of brain stem vascular malforma tions we reviewed our 5-year experience in 50 patients evaluated betwe en 4 and 51 months (mean, 25 months) after radiosurgery. Twenty-eight patients (56%) underwent gamma unit radiosurgery for symptomatic arter iovenous malformations (AVMs), and 22 patients (44%) for angiographica lly occult vascular malformations (AOVMs). Patients varied in age from 7 to 76 years (mean, 39 years). Forty-one patients (82%) had from 1 t o 5 hemorrhages prior to gamma knife radiosurgery. Ten (20%) had one o r two prior unsuccessful operations, and 37 (74%) presented with a neu rological deficit. Of the patients with AVMs, 6 were considered Spetzl er Grade III, and 22 (79%) Grade VI (inoperable: major component withi n the brain stem parenchyma). Forty-four malformations (88%) were adja cent to or within the midbrain and pons, the remainder involved the me dulla. Average malformation diameters varied from 6 to 30.4 m (mean, 2 0.6; mean volume 4614 mm3). The minimal radiation dose to the margin o f the malformations ranged from 12 to 25.6 Gy (mean, 18.9 Gy). Of the 28 patients with AVMs, 8 had follow-up angiograms at a minimum of 2 ye ars after radiosurgery (or sooner if their MRIs suggested obliteration ). Of these patients, 7 (88%) showed complete obliteration of their ma lformations. No patients with AOVMs rehemorrhaged if more than 15 mont hs elapsed after radiosurgery. Four patients (8%; two with AVMs and tw o with AOVMs) sustained a symptomatic re-hemorrhage during the follow- up period. New neurologic deficits related to radiosurgery occurred in 10 patients. Three were temporary with return to baseline function at an average of 15 months post-radiosurgery. Of the remaining 7 patient s with new deficits (14%), 3 were improving at last follow-up, and one patient died 35 months after radiosurgery of presumed radiation injur y. Precise gamma unit radiosurgery provides a safe and effective manag ement strategy for brain stem vascular malformations. Its use is parti cularly valuable for malformations considered unsuitable for microsurg ical resection.