“…[1,13] EVPs are variously attributed to: vascular anomalies such as IVC thrombosis/ hypoplasia, iliac vein stenosis, obesity related IVC obstruction, bladder distention, intracranial hypotension, previous microdiscectomy, coagulopathy, Factor V Leiden mutation, protein C deficiency, Behcet's, and Budd-Chiari syndrome. [18,22] ese conditions block normal venous drainage into or through the IVC, and divert blood flow into collaterals through the vertebral venous plexus; this results in venous engorgement and compression of the thecal sac, nerve roots, or cauda equine. [22] Encountering unanticipated EVPs during lumbar surgery…”