Background and Purpose--To clarify hemodynamic risk factors for hemorrhage in arteriovenous malformations (AVMs), the mean transit time (MTT) of feeding arteries and draining veins in AVMs with and without hemorrhage was measured and analyzed.

Methods--Morphological features such as the number and diameter of draining and feeding vessels and the AVM nidus volume were evaluated in 30 patients with supratentorial AVMs. The MTT of feeding arteries and draining veins was measured with the use of time-density curves obtained by digital subtraction angiography. The correlation between hemorrhage and morphology and hemorrhage and MTT was analyzed statistically.

Results--The nidus volume was not significantly different between hemorrhagic and nonhemorrhagic AVMs. However, between ruptured and unruptured AVMs there was a significant difference in the mean number of draining veins (1.5±0.69 versus 2.3±0.50; P=0.006), the MTT of the feeding artery (1.10±0.24 versus 1.62±0.55; P=0.03), and the ratio of the MTT of the draining to the feeding vessels (1.71±0.43 versus 1.05±0.07; P<0.001).

Conclusions--A high ratio of the MTT of draining veins to feeding arteries suggests disequilibrium between nidal inflow and outflow. The consequent increased pressure in the draining vein may contribute to the development of AVM hemorrhage.