Congested residual nidus after preoperative intranidal embolization in midsize cerebral arteriovenous malformations of 3-6 cm in diameter.

Background: Modern delicate microcatheters allow intranidal embolization of cerebral arteriovenous malformations (AVM). The aim of the current analysis was to assess effects of preoperative intranidal deployment of embolic material on surgical time and blood loss in cerebral arteriovenous malformations of 3-6 cm in diameter.

Methods: The case records of 38 cerebral AVM between 3 and 6 cm in maximum diameter were reviewed, that had been embolized intranidally with N-butyl 2-cyanoacrylate (Histacryl) and subsequently operated on. Surgical time and blood loss as well as particular intraoperative findings such as a congested nidus and thrombosis of draining veins were registered and correlated with the extent of embolization and the time interval between embolization and surgery.

Findings: Preoperative embolization occluded an estimated range of 10 to 90% of the nidus. Minor embolization related bleeding without clinical relevance occurred in 5 patients. Significant embolization related bleeding resulting in earlier than planned surgery occurred in another 5 patients. All embolization related haemorrhages occurred within 24 hours. Average total operating time was 343+/-106 min and average blood loss was 684+/-858 ml. Unequivocal bleeding difficulty from the nidus and a total blood loss of more than 1000 ml were encountered in 7 instances and dissection was tedious due to a bleeding AVM core in 5 other cases. A congested AVM core was the source of bleeding in 11 patients and paraventricular neovascularization in one. 6 of the 11 cases with a congested AVM core had suffered minor or substantial haemorrhage after a preoperative endovascular procedure. Intraoperative nidus congestion was noted in this series after an interval as long as 2 weeks after the last embolization. Combined management resulted in permanent morbidity in 6 of the 38 cases. In 4 of them the neurological deficit was associated with an intraoperative bleeding problem, in all due to congested nidus. Morbidity had to be correlated with major haemorrhage resulting from preoperative embolization in 2 instances.

Conclusions: Intranidal embolization prior to surgical removal of AVM can lead to a congested residual nidus and intraoperative bleeding. Minor leakage after preoperative embolization is an inconsistent warning sign of nidus congestion. Nidus outflow after intranidal embolization appears to require a few weeks for normalization. Delay of surgery after embolization should be considered in cases of suspected congested residual nidus. The danger of major haemorrhage or arterial revascularization during this waiting period appears small.