Cauda Equina Syndrome Due to Spinal Subdural Hematoma Mimicking Epidural Hematoma: The "Tense Bluish Dura" Intraoperative Clue.

Spontaneous spinal subdural hematoma is an uncommon cause of acute cauda equina syndrome that can closely resemble spinal epidural hematoma on magnetic resonance imaging (MRI). This report describes an intraoperative dural appearance that may help identify subdural pathology when imaging suggests an epidural source. A 73-year-old woman receiving apixaban for recurrent pulmonary embolism presented with sudden lumbar pain radiating to both legs, followed by right-sided leg weakness and urinary retention. MRI showed a dorsal collection from L1 to L3 reported as an epidural hematoma, with a right L1-L2 facet joint cyst supporting this interpretation. She underwent urgent L1-L4 laminectomy. After epidural decompression and facet cyst removal, the dura remained tense, nonpulsatile, and bluish. This appearance prompted a midline durotomy, which revealed an intact arachnoid and a dark, organizing subdural hematoma. The clot was evacuated, and the cauda equina was decompressed. Radicular pain resolved immediately. At two weeks, the left leg had fully recovered, and the right leg showed partial improvement. At three months, she was walking independently with full neurological recovery. A brief literature review identified similar intraoperative descriptions of dural discoloration and persistent tension when imaging did not clearly distinguish epidural from subdural collections. A tense, nonpulsatile, bluish dura after epidural decompression may indicate an underlying subdural hematoma. Recognition of this appearance can guide dural exploration, especially in anticoagulated patients with additional findings that may influence MRI interpretation.