Vascular anatomy in the lumbar spine investigated by three-dimensional computed tomography angiography: the concept of vascular window.

OBJECTIVE: To report an in vivo anatomic evaluation of prevertebral vessels in the lumbar spine using three-dimensional (3D) computed tomography (CT) angiography and to develop the concept of vascular window for surgical access to L4-5 and L5-S1 disks.

METHODS: In 146 patients who were scheduled for anterior lumbar spine surgery, 3D CT angiography was performed preoperatively. Spinal disorders included degenerative disk disease (n = 120) and low-grade spondylolisthesis (n = 26). 3D reconstructions were obtained using the volume-rendering technique. Level of aortic bifurcation and iliocavum confluence, presence of the ascending iliolumbar vein, presence of the central sacral vessels, and anatomic variations were analyzed. A vascular window at L5-S1 was defined as the "free vascular" area for the anterior part of the L5-S1 disk. A vascular window at L4-L5 was defined as the "free vascular" area for the left anterolateral part of the L4-5 disk.

RESULTS: The level of aortic bifurcation was most often observed at L4 (64%). The iliocavum confluence occurred most frequently at L5 (44%). The iliolumbar ascending vein and central sacral vessels were identified in 84% and 72% of cases. Five (3.5%) anatomic variations were noted: right internal iliac vein draining into the left common iliac vein in two cases and tortuous vessels in three cases. A vascular window was measured to 34.5 mm ± 12 at L5-S1 and to 23 mm ± 8 at L4-L5. The vascular window was <25 mm in approximately one in four patients at L5-S1 and in approximately two in three patients at L4-L5.

CONCLUSIONS: This study confirms that vascular anatomy in the lumbar spine is characterized by a great variability that has significance for preoperative assessment. 3D CT angiography allowed for an effective evaluation of the relationships between the prevertebral vessels and the intervertebral disks at L4-L5 and L5-S1. Although adherence of vessels to the anterior ligament cannot be predicted by this technique, the concept of vascular windows investigated preoperatively by CT angiography could be helpful in predicting the need for vessel mobilization during anterior lumbar spine surgery.