Pseudo Subarachnoid Hemorrhage Sign in Bacterial Meningitis in a Patient Presenting With Acute Ischemic Stroke: A Novel Radiological Clue to Rapid Diagnosis

Pseudo subarachnoid hemorrhage (SAH) is an entity defined when characteristic computed tomography (CT) findings of SAH are seen without evidence of hemorrhage on MRI, autopsy, or cerebrospinal fluid analysis. This imaging phenomenon has been reported in association with multiple clinical settings including diffuse cerebral edema, hypoxic-ischemic injury, post percutaneous coronary intervention, and the focus of our report, acute bacterial meningitis. The mechanisms leading to this finding are poorly understood. Current hypotheses explaining this pattern vary widely depending on the associated pathology. In this report, we present a case of pseudo SAH associated with bacterial meningitis and a literature review on the causes, neuroimaging findings, and mechanisms associated with pseudo SAH. We discuss dual energy CT as a possible tool for differentiating pseudo SAH from true SAH. We analyze the timing of imaging studies and the role timing plays in the presentation of the pseudo SAH sign. We conclude that the extravasation of iodine contrast into the subarachnoid space can mimic SAH on CT. Ultimately, our case adds to the growing body of evidence that clinicians should be aware of acute bacterial meningitis as a potential mimic of SAH on CT.