Gamma knife outcome models as a reference standard in the embolization of cerebral arteriovenous malformations

Background. We sought to utilize outcome models from gamma knife radiosurgery (GKRS) to cerebral arteriovenous malformations (AVM) as a reference standard in assessing the clinical outcome of embolization, thus comparing the outcomes of two different management alternatives, in the same patients. Methods. 87 consecutive patients with 88 AVM were admitted during 1997-1999 for initial embolization of an AVM. The clinical outcomes were recorded prospectively. Angiography under stereotactic conditions with measurement of AVM volume was performed before and after embolization. GKRS outcome models were used to predict obliteration rate, complication rate and risk of hemorrhage before and after embolization. The clinical outcome of embolization followed by predicted outcome of adjunct GKRS was then compared with the predicted outcome of GKRS as the only treatment. Findings. Eight patients were subjected to microcatheterization but not to embolization. By the end of the study period, embolization had been terminated in 55 patients out of 80 (69 %). The predicted outcome of GKRS alone was 58 obliteration and 12 complications while that of the combined management was 58 obliteration and 15 complications. The difference was not significant an the p < 0.1 level.Interpretation. Volume measurement from angiography and outcome models from gamma knife radiosurgery are useful as a reference standard in the management of AVM. Absolute volume reduction from embolization is most prominent for AVM > 10 ml and thus facilitates subsequent radiosurgery. For AVM ≤ 10 ml, GKRS as the only treatment can be an alternative to primary embolization, particularly if no significant volume reduction or obviously beneficial effect of targeted embolization is expected. Further prospective studies are needed to identify subgroups in which one treatment has advantages over the other. (author)