Subarachnoid Mirage: A Case of Pseudosubarachnoid Hemorrhage.

A 22-year-old man with a history of intravenous methamphetamine use presented with severe headache for 5 days, was afebrile, and had nuchal rigidity. Computed tomography and magnetic resonance imaging results were interpreted as revealing acute subarachnoid hemorrhage. Twenty-four hours later, he developed acute neurologic deterioration. A lumbar puncture was performed, revealing the presence of Staphylococcus aureus. The false-positive image mimicking blood was potentially a result of an extremely high protein concentration present in the cerebrospinal fluid, provoked by an intense inflammatory reaction leading to disruption of the blood-brain barrier. Pyogenic meningitis is one of the causes of pseudosubarachnoid hemorrhage, or a false diagnosis of subarachnoid hemorrhage, when one does not actually exist.