Surgical Relevance of the Venous Anatomy of Prepsoas Space: An Anatomic Study and Radiographic Review of 516 Patients

Introduction: During lateral L2-L5 interbody fusion, retroperitoneal anatomy is often unfamiliar because of limited visualization through long/narrow minimally-invasive retractor systems. Venous anatomy anterior to the psoas muscle holds particular importance with antepsoas approaches, in which unexpected bleeding can impede operations. Venous anatomy thus represents challenges in the anterior-to-psoas surgery. Our objective is to define venous anatomy and interpret preoperative image findings that may portend aggressive intraoperative bleeding for the prepsoas approach to the lateral L2-L5 interbody fusion.

Methods: All patients undergoing anterior or lateral lumbar interbody fusions by four surgeons at a single institution over seven years were retrospectively reviewed. Only patients with preoperative MRI and/or CT myelogram of the lumbar spine were included. Images were screened for aberrant venous anatomy, with particular emphasis on left renal veins because of the implications in dilated venous vasculature in the prepsoas space.

Results: Of 516 patients who met inclusion criteria, fifteen images demonstrated prominent lumbar, ascending lumbar, and/or reno-lumbar veins which are a collection of antepsoas vessels communicating with the vena cava, iliac branches, and renal/ gonadal veins. Lumbar veins may also drain into the ascending lumbar vein, which ascends between the psoas muscle and the lumbar vertebrae. Most common indications for engorgement of anterior-to-psoas veins were an aberrant left renal vein: eleven (2%) and three (0.5%) patients had a retro-aortic and circumferential left renal vein, respectively. This abnormal anatomy causes the aorta to compress –and subsequently enlarges– the left renal vein, which in turn distends the reno-lumbar veins and ascending lumbar vein. Alternatively, the “nutcracker” phenomenon may compress the left renal vein between the aorta and superior mesenteric artery. When prepsoas veins dilate, flow voids are readily appreciated on preoperative MRI.

Conclusion : Identifying flow voids in prepsoas spaces most commonly represents dilated lumbar, ascending lumbar, and/or reno-lumbar veins. These preoperative image findings may foretell aggressive intraoperative bleeding during prepsoas approaches to lateral L2-L5 interbody fusion. Importantly, these veins can be swiftly coagulated or clipped early in the operation without physiologic consequence.