A 46-year-old woman had a sudden cardiopulmonary arrest directly after a surgical procedure. She was resuscitated twice for 15 minutes each time; however, despite return of spontaneous circulation, the patient never regained consciousness. Noncontrast head computed tomography (CT) findings 1 day after resuscitation were unremarkable. Forty-eight hours later, a repeated head CT showed the development of extensive cerebral edema, effacement of the sulci, slitlike ventricles, and apparent subarachnoid hemorrhage (image, arrow) with effacement of the basal cisterns. However, the hyperattenuation of the subarachnoid space was lower than would be expected in true subarachnoid hemorrhage, suggesting pseudosubarachnoid hemorrhage. Because of the patient's poor prognosis, the decision was made to withdraw care. 

Pseudosubarachnoid hemorrhage is a CT sign that is commonly due to cerebral edema from anoxic ischemic encephalopathy.^1-3 Other causes include severe leptomeningitis, intrathecal contrast, and venous sinus thrombosis.^1,4 Hounsfield unit (HU) measurements on CT can help distinguish true subarachnoid hemorrhage from pseudosubarachnoid hemorrhage: the hyperattenuation of the subarachnoid space is lower in pseudosubarachnoid hemorrhage (30-40 HU) than in true subarachnoid hemorrhage (60-70 HU).