Gamma Knife outcome models as a reference standard in the embolisation of cerebral arteriovenous malformations

Background. We sought to utilise outcome models from Gamma Knife radiosurge ry (GKRS) to cerebral arteriovenous malformations (AVM) as a reference stan dard in assessing the clinical outcome of embolisation, 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 embolisation of an AVM. The clinical outcomes were recorded pr ospectively. Angiography under stereotactic conditions with measurement of AVM volume was performed before and after embolisation, GKRS outcome models were used to predict obliteration rate, complication rate and risk of haem orrhage before and after embolisation. The clinical outcome of embolisation followed by predicted outcome of adjunct GKRS was then compared with the p redicted outcome of GKRS as the only treatment. Findings. Eight patients were subjected to microcatheterisation but not to embolisation. By the end of the study period, embolisation had been termina ted in 55 patients out of 80 (69%). The predicted outcome of GKRS alone was 58 obliterations and 12 complications while that of the combined managemen t was 58 obliterations and 15 complications. The difference was not signifi cant on 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 managem ent of AVM. Absolute volume reduction from embolisation is most prominent f or AVM > 10 ml and thus facilitates subsequent radiosurgery. For AVM less t han or equal to 10 ml, GKRS as the only treatment can be an alternative to primary embolisation, particularly if no significant volume reduction or ob viously beneficial effect of targeted embolisation is expected, Further pro spective studies are needed to identify subgroups in which one treatment ha s advantages over the other.