PERINIDAL HYPERVASCULAR NETWORK ON IMMEDIATE POSTOPERATIVE ANGIOGRAM AFTER REMOVAL OF LARGE ARTERIOVENOUS-MALFORMATIONS LOCATED DISTANT FROM THE ARTERIAL CIRCLE OF WILLIS

UNEXPLAINED INTRAOPERATIVE OR postoperative hemorrhage occurs in certa in cases in the surgery of large arteriovenous malformations (AVMs), w hich are defined as those with maximal diameter of the nidus larger th an 5 cm. Immediate postoperative angiograms were evaluated with refere nce to whether such hemorrhage could be predicted. Immediate postopera tive angiograms were taken in 12 patients with large AVMs on the day a fter the operation during which the AVM was removed. In five of six AV Ms located in the distal cerebral hemisphere, a hypervascular network was seen in the vicinity of the removed nidus on the immediate postope rative angiogram. The unexplained hemorrhage occurred in four of the f ive cases with the hypervascular network. In the remaining six patient s with AVMs, the hypervascular network was not observed and they did n ot develop hemorrhage; the AVMs were located either close to the arter ial circle of Willis or in the cerebellum. We believe that the hyperva scular network seen on the immediate postoperative angiogram after the removal of a large distal AVM is an important sign predicting the lik elihood of unexplained intraoperative and postoperative hemorrhage dev elopment. We call this perinidal hypervascular network ''modja-modja v essels'' because it resembles shaggy hair. The mechanism of its appear ance and the pathogenesis of the unexplained intraoperative and postop erative hemorrhage are discussed.