Object: The aim of this study was to identify the natural history of untreated cerebral arteriovenous malformations (AVMs) and the risk factors for subsequent hemorrhage after an initial AVM diagnosis.
Methods: The authors studied 305 consecutive patients with AVMs at the Kyoto University Hospital between 1983 and 2005. These patients were followed up until the first subsequent hemorrhage, the start of any treatment, or the end of 2005. Possible risk factors that were investigated included age at initial diagnosis, sex, type of initial presentation, size and location of the AVM nidus, and the venous drainage pattern. Subsequent hemorrhage occurred in 26 patients from the hemorrhagic group during 380 patient-years, and in 16 patients from the nonhemorrhagic group during 512 patient-years.
Results: The annual bleeding rate in the hemorrhagic group was 6.84% after the initial hemorrhage; however, that rate decreased in the first 5 years (15.42% in the first year, 5.32% in the subsequent 4 years, and 1.72% in more than 5 years). In the nonhemorrhagic group (annual bleeding rate of 3.12%), the patients initially presenting with headaches (annual bleeding rate of 6.48%) or asymptomatic presentations (annual bleeding rate of 6.44%) had a higher risk for subsequent hemorrhage. Conversely, those patients presenting with seizures (annual bleeding rate of 2.20%) or neurological deficits (annual bleeding rate of 1.73%) had a lower risk. A significantly increased risk (p < 0.05) of rebleeding was found among children (hazard ratio [HR] = 2.69), females (HR = 2.93), or patients with deep-seated AVMs (HR = 3.07).
Conclusions: Children, females, and patients with deep-seated AVMs had a threefold increased risk of rebleeding after an initial cerebral AVM. This increased risk was highest in the first year after the initial hemorrhage, and thereafter gradually decreased.