Acute Subdural Hematoma Without Subarachnoid Hemorrhage Due to Traumatic Aneurysm of the Posterior Cerebral Artery

Acute subdural hematoma (ASDH) typically results from high-energy head trauma, such as motor vehicle accidents or severe falls. It can also be caused by minor head injuries in elderly individuals due to damage to bridging veins or small arteries, but it is considerably rarer in younger patients. A previously healthy 39-year-old man presented with progressive headaches and consciousness disturbance. The emergent computed tomography (CT) revealed ASDH covering most of the left cerebral hemisphere without subarachnoid hemorrhage (SAH). CT angiography (CTA) showed an irregularly shaped aneurysm at a distal branch of the left posterior cerebral artery (PCA) (quadrigeminal segment (P3 segment)/cortical segment (P4 segment)), suggesting that ASDH was caused by aneurysmal bleeding of the PCA. Digital subtraction angiography performed after a left decompressive craniectomy showed the aneurysm observed on CTA was suspected to be a pseudo-aneurysm, and parent artery occlusion was performed. This report presents a rare case of ASDH in a young individual without a history of head trauma. Our case highlights the importance of considering aneurysm rupture as a potential etiology in patients with ASDH without SAH, particularly in the absence of a history of head trauma.