Pseudo-subarachnoid hemorrhage: report of three cases and review of the literature.

Subarachnoid hemorrhage (SAH) appears on CT as hyperdensity in the subarachnoid space. In rare circumstances a similar appearance may occur in the absence of subarachnoid blood, a finding that has been termed "pseudo-subarachnoid hemorrhage." We describe three patients who presented with abrupt alterations in mental status in whom CT falsely suggested SAH, and we review the literature regarding this imaging finding. In contrast to prior reports, all three of our patients had a favorable outcome.