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Detailed follow-up results for 25 patients treated for cerebral arteriovenous malformation (AVM) with a gamma unit are presented. Complete nidus obliteration was angiographically confirmed in 16 (73%) of 22 cases receiving full-dose irradiation. There were no radiation- or AVM-related mortalities. However, we did experience one case of radiation-related morbidity and one of angiographyrelated mortality, the autopsy findings of which are discussed. Computed tomography scan and magnetic resonance imaging follow-up studies of radiosurgically treated AVMs indicated that increased enhancement of the nidus after contrast or gadolinium administration could persist even after obliteration of the AVM was angiographically confirmed.

BACKGROUND Following radiosurgical treatment, the majority of patients with arteriovenous malformations (AVMs) are periodically examined by means of computed tomography (CT) and magnetic resonance imaging (MRI) to assess the attainment of nidus obliteration, as well as adverse radiation effects in the surrounding brain. However, few neuroimaging studies of the long-term results following complete obliteration, confirmed by angiography, have been published to date. METHODS CT, MRI, magnetic resonance (MR) angiographic and angiographic images, obtained after angiographic confirmation of complete nidus obliteration, were reviewed in 11 AVM patients treated with gamma knife radiosurgery. The period between angiographic confirmation of nidus obliteration and these most recent examinations was 12–84 months (mean, 29 months). RESULTS In ten patients who were assessed by CT, the obliterated nidus was shown to be isodense (eight cases) or a mixture of isodense and hypodense areas (two cases). A significant time-related decrease in contrast enhancement was observed within 1 to 2 postobliteration years (five/seven cases). Eight patients were evaluated by MRI. On T1-weighted imaging, the nidus was shown to be hypointense (six cases) or a mixture of hypointense and isointense areas (two cases). On T2-weighted imaging, nidus intensity varied more than that observed on T1-weighted imaging, and time-related intensity increases were observed (two/seven cases). No flow-signal void was demonstrated in any of these cases. In four of the seven cases, in which serial postobliteration follow-up MRI studies were conducted, significant gadolinium enhancement persisted 3 years or more after obliteration (maximum of 7 years). No vascular abnormalities were demonstrated in seven patients who were assessed by conventional angiography and/or MR angiography. CONCLUSIONS Radiosurgery-induced changes in a nidus may continue for several years after angiography has shown complete AVM obliteration.

Long-term follow-up results of nine children treated for cerebral arteriovenous malformation with a gamma unit are presented. Complete nidus obliteration was angio-graphically confirmed in six cases and significant decreases in arteriovenous malformation size were observed in the other three. There were no radiation-related deteriorations in physical or mental development. In seven patients who underwent endocrinological examination more than 3 years after irradiation, five were normal and the other two showed only low serum adrenocorticotropic hormone levels, which, however, did not necessitate replacement therapy. Neurodiagnostic imaging follow-up studies revealed no radiation-induced lesions in any of the nine cases.