Radiological, clinical, and pathological findings in pseudosubarachnoid hemorrhage.

A pseudo-subarachnoid hemorrhage is a false positive finding on CT head examination. The scan appears positive for a subarachnoid hemorrhage. This is not substantiated by subsequent neuropathologic findings. We describe three patients with anoxic encephalopathy that appear to have diffuse subarachnoid hemorrhage on CT examination. Autopsy photographs provide pathological correlation. Review of the medical literature includes six additional reports of this phenomenon. None of these patients had subarachnoid hemorrhage. CT scans of normal patients show the cranial bone lined by a thin layer of dura mater. This overlies the subarachnoid space filled with cerebrospinal fluid (CSF). The average width of this space varies, increasing with age. With brain swelling due to acute hypoxic encephalopathy, the cerebral cortex becomes displaced into areas normally occupied by CSF and veins become congested. The increased average tissue density immediately deep to the dura and superficially within the cerebral sulci results in hyperdensity on unenhanced CT, simulating the appearance of subarachnoid hemorrhage. On CT examination, a patient with hypoxic ischemic encephalopathy can show increased density in the subarachnoid space. This can be erroneously interpreted as subarachnoid hemorrhage. Our experience and a review of the literature suggest that this condition is not rare and is being misdiagnosed with some regularity. Radiologists, neurologists, and neurosurgeons should avoid this pitfall.

W. Mel Flowers, Jr, MD, George Benashvili, MD, and Jonathan Fratkin, MD. Departments of Radiology and Pathology, University of Mississippi Medical Center, Jackson, MS.