GAMMA-KNIFE SURGERY FOR PREVIOUSLY IRRADIATED ARTERIOVENOUS-MALFORMATIONS

OBJECTIVE: The goal was to report the treatment results after a second gamma knife treatment and to compare them with the results obtained a fter a first gamma knife treatment, as well as to investigate whether the models to predict the results after a first treatment are also app licable after gamma knife treatment of previously irradiated arteriove nous malformations. METHODS: The number of complications and the postt reatment hemorrhage rate were recorded for 112 patients in the study, and the number of obliterations was recorded for the 101 patients for whom conclusive angiograms were obtained. The results were compared wi th the expected results after a first gamma knife treatment. RESULTS: The observed number of obliterations was 62, which is not significantl y different from the predicted number of 65. There were 14 observed an d 5 predicted complications. When the risk from the preceding radiatio n treatment was added, the observed number of complications was simila r to the predicted number. Six hemorrhages were observed after the sec ond treatment. Of the 5 patients with unchanged arteriovenous malforma tion size after both the first and second treatments, 2 experienced he morrhages after the second treatment, compared with none among the 81 patients for whom the malformation was obliterated or significantly de creased in size after the second treatment. CONCLUSIONS: The obliterat ion rate after gamma knife surgery for previously irradiated arteriove nous malformations is similar to that after primary gamma knife treatm ent. The complication rate increases with the amount of radiation prev iously given. The incidence of posttreatment hemorrhages is lower in t he latency period if the malformation is affected by the radiation.