Nontraumatic Pure Acute Subdural Hematoma Caused by a Ruptured Cortical Middle Cerebral Artery Aneurysm: Case Report and Literature Review.

Nontraumatic or "spontaneous" acute subdural hematoma (SDH) is rare, and "pure" acute SDH without subarachnoid hemorrhage (SAH) due to aneurysmal rupture is extremely rare. We report a case of nontraumatic pure acute SDH caused by the rupture of a cortical middle cerebral artery (MCA) aneurysm. A 43-year-old man with no antecedents, except hypertension, presented to the emergency department with acute-onset moderate headache and nausea after swimming. He reported neither preceding head trauma nor dental check-up. Neurological examinations and laboratory tests were unremarkable. Computed tomography (CT) showed an acute SDH on the left convexity without SAH, but both magnetic resonance (MR) angiography and three-dimensional CT (3D-CT) angiography disclosed no vascular abnormality. As he became drowsy, the patient emergently underwent an evacuation of the SDH. Unexpectedly, a small saccular aneurysm of a cortical branch of the left MCA was recognized at surgery. Although indocyanine green (ICG) angiography revealed this aneurysm was thrombosed, a clip was applied on the aneurysmal base. He was discharged home without any complications 21 days after admission. To seek the cause of nontraumatic acute SDH, supplementary examinations including 3D-CT, MR, and/or catheter angiography are necessary. Even if angiography reveals no vascular lesions, the present case warrants that the cortical surface should be meticulously inspected at surgery, because a thrombosed cortical artery aneurysm might be an underlying cause.