A misleading distal anterior cerebral artery aneurysm

BACKGROUND Aneurysmal rupture causing pure acute subdural hematoma (aSDH) is rare. In the four previously reported cases of distal anterior cerebral artery (ACA) aneurysm resulting in pure aSDH, blood distribution in the interhemispheric (IH) space has systematically incriminated the distal ACA as the source of rupture. We present a misleading case of a distal ACA rupture resulting in convexity aSDH with minimal IH blood. CASE DESCRIPTION A 51-year-old patient presented in coma with decerebrate posturing and a blown left pupil from a left convexity acute hemispheric subdural hematoma. She underwent urgent left craniectomy and subdural hematoma evacuation. Given the absence of identifiable etiology, including trauma, we performed an immediate postoperative Computed tomography-angiography (CTA) in order to rule out an underlying cause. The CTA revealed an aneurysm originating from the callosomarginal artery branch of the ACA. Although the minimal amount of IH blood and the remote distance of convexity blood from the aneurysm suggested that it may be a fortuitous finding, we considered the possibility that the two might be related. The patient underwent surgical aneurysm clipping, confirming that it had ruptured and allowing complete aneurysm obliteration. Following the procedure, the patient's neurological and functional status gradually improved. CONCLUSION Ruptured distal ACA aneurysms may present with convexity isolated aSDH with minimal IH blood. Quantity and distribution of isolated aSDH can be misleading and is not always a reliable predictor of aneurysm location. Misinterpretation of the aneurysm as an incidental finding would lead to improper management with potentially serious consequences.