The physiological and anatomical aberrations that result in hemorrhage from cerebral arteriovenous malformations (AVMs) remain unclear. In an attempt to clarify which conditions may predispose to hemorrhage, we examined clinical and physiological indices on presentation groups of either hemorrhage or nonhemorrhage in a large cohort of patients (n = 449). Variables examined included AVM size, type of venous drainage, transcranial Doppler (TCD) velocities, feeding mean arterial pressure (FMAP), and draining vein pressure. TCD and pressure data were obtained before any treatment. Age (mean +/- standard deviation) at the time of presentation was 33 +/- 13 years and did not differ between groups. Patients with small (< or = 2.5 cm) AVMs presented more frequently with hemorrhage (90%) than did patients with medium (> 2.5 and < or = 5.0 cm; 52%) or large (> 5.0 cm; 50%) AVMs (P = 0.0001). The 48 of 94 AVMs (51%) with deep venous drainage were more likely to have hemorrhage (P = 0.0219) than were those with superficial drainage (24 of 73 [33%]). Deep drainage was a predictor of hemorrhage even in the subgroup of medium and large supratentorial AVMs (P = 0.005). There was no difference in draining vein pressure (n = 18) between groups (21 +/- 10 and 19 +/- 11 mm Hg, respectively; P = 0.7812). FMAP (n = 52) was higher in the hemorrhage than in the nonhemorrhage group (44 +/- 13 versus 34 +/- 10 mm Hg; P = 0.0007) but was only weakly related to the size of the lesion (largest dimension) (y = -0.74x + 40; r = 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)