Aspirin Use and Risk of Subdural Hematoma: Updated Meta-Analysis of Randomized Trials

Subdural hematomas are an uncommon, but a serious, bleeding complication of antithrombotic therapies. We update our previous inconclusive meta-analysis to better estimate the risk of subdural hematoma associated with aspirin use.

For the initial meta-analysis, nine randomized trials published between1980 and 2012 comparing aspirin with placebo/control were considered. Additional data from four large primary prevention trials were added. Two reviewers independently extracted data on subdural hematomas, with differences resolved by joint review and consensus.

Numbers of subdural hematoma were available from thirteen randomized trials involving 155,554 participants comparing aspirin (dosage range 25 mg twice daily to 325 mg daily) to placebo (ten double-blind trials) or no aspirin (three trials). Participants included healthy healthcare providers, older people with vascular risk factors without manifest vascular disease, and those with atrial fibrillation or chronic angina. Pooling all trials, subdural hematomas were identified in 93 of 77,698 participants assigned to aspirin versus 62 of 77,856 participants assigned to placebo/no aspirin. By meta-analysis, the relative risk ratio_meta of subdural hematoma associated with assignment to aspirin was 1.5 (95%CI 1.1, 2.0, p = 0.01; p = 0.9 for heterogeneity, I² index = 0%). Based on recent primary prevention trials, subdural hematoma diagnosis averaged 1 per 3,125 people per year without aspirin use; the absolute increase associated with aspirin use was estimated as one additional subdural hematoma per 6,500 patients annually.

This meta-analysis confirms that aspirin use increases the relative risk of subdural hematoma, but the absolute increased rate associated with aspirin therapy is very low for most people.