Non-traumatic subdural hemorrhage: beware of ruptured intracranial aneurysm.

Acute subdural hemorrhage (SDH) is commonly encountered by emergency radiologists in the setting of trauma. When history or imaging evidence of trauma is absent, the differential diagnosis for SDH should be expanded. Intracranial aneurysm rupture is a rare and underrecognized cause of SDH which may present without concurrent subarachnoid hemorrhage. The mechanism of aneurysmal SDH is controversial, but understanding the anatomic microenvironment of the aneurysm provides insight and clarifies aneurysm features predisposing to subdural compartment rupture. Aneurysmal SDH is a neurosurgical emergency and its treatment strategies differ from traumatic SDH. Outcomes are poor if treatment is delayed; thus, radiologists play a central role in recognizing this uncommon but potentially devastating complication of aneurysm rupture. The goal of this article is to familiarize radiologists with clinical and imaging characteristics of aneurysmal SDH and review pertinent anatomy, risk factors, and potential etiologies. Aneurysmal rupture can easily be overlooked in the routine workup of atraumatic SDH, and radiologists must know when to recommend vascular imaging to avoid the catastrophic consequences of a missed diagnosis.