Pseudo-Subarachnoid Hemorrhage After Spinal Myelography Mimicking Acute Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a life-threatening condition typically diagnosed on non-contrast computed tomography (CT) by the presence of hyperdense blood within the subarachnoid spaces. However, several non-hemorrhagic conditions can mimic this appearance, a phenomenon known as pseudo-subarachnoid hemorrhage (pseudo-SAH). Among these, contrast-related pseudo-SAH has been increasingly recognized following diagnostic and therapeutic procedures. We report a case of pseudo-SAH caused by migration of intrathecal contrast medium after spinal myelography that initially mimicked spontaneous SAH on CT. Head CT demonstrated diffuse high attenuation within the subarachnoid spaces, with attenuation values higher than typically observed in true SAH. Follow-up CT revealed rapid resolution of the hyperdense areas. Based on these findings and the recent history of myelography, a diagnosis of contrast-related pseudo-SAH was made. This case highlights that careful evaluation of clinical history, CT attenuation values, and temporal changes in imaging findings is essential for differentiating pseudo-SAH from true SAH. Awareness of this entity may help avoid unnecessary invasive investigations and inappropriate management.