[Bilateral chronic subdural hematoma in a young adult mimicking subarachnoid hemorrhage].

A 33-year-old man was admitted to our hospital with a sudden severe headache five days after the onset CT scan showed a slight high-density area in the basal cistern, mimicking subarachnoid hemorrhage (SAH), and diffuse brain swelling. However, conventional cerebral angiography and CT angiography failed to demonstrate aneurysms and vascular malformations. MRI showed bilateral subdural hematoma, but no SAH. Irrigation of liquefied subdural hematoma, causing high intracranial pressure, was carried out. Postoperative course was uneventful and his headache resolved within a day. The author presented a case of bilateral chronic subdural hematoma who presented with a sudden severe headache mimicking a SAH. Hyper attenuation in the basal cistern and subarachnoid space in CT, don't always indicate SAH. MRI, including fluid-attenuated inversion recovery (FLAIR) sequences, is useful in differentiating the "pseudo" SAH from "true" SAH, and lead to the right diagnosis.