Spinal Epidural Space Anatomy and Contents

The spinal epidural space is a space between the dura and the ligamentum flava and periosteum of the vertebral bodies, pedicles and laminae. The epidural space is most capacious at the upper thoracic levels. Measurements of posterior space in adults is approximately 0.4 mm at C7-T1, 7.5 mm in upper thoracic levels, 4.1 mm at T11-12 levels and 4-7 mm in lumbar levels.2 The anterior dura is fused with the posterior longitudinal ligament and the annular ligament at the level of each intervertebral disc, which divide the anterior epidural space into vertical segments separated by midline plica mediana dorsalis. The plica, meningo-vertebral ligaments and lateral connective tissue strand (peridural membrane) divide the epidural space into lateral halves as well as anterior and posterior compartments (Fig-1a-d). The posterior longitudinal ligament separates from the anterior dura at the lumbosacral junction and the anterior epidural space becomes filled with fat more inferiorly. A rich valveless network of veins is another important content of this space.4,5 The intraosseous vertebral veins drain into the central basivertebral vein. The basivertebral vein drains into the retrovertebral venous plexus in the anterior epidural space located on the posterior aspect of the midvertebral body. The retrovertebral venous plexus has a medial meshwork and longitudinal bilateral components, the anterior internal vertebral veins. The retrovertebral venous plexus drains laterally via the supra- and infrapediculate radicular veins through the lateral nerve root canal. The radicular veins drain into the paravertebral ascending lumbar veins in the costovertebral grooves. These paravertebral veins connect with the caval system via the lumbar segmental veins located in the lateral waist of the vertebra. There is lack of lymphatics and lymph nodes in the space and thus, all pathologies involving the space are blood borne. The radicular veins are valveless and may be associated with the contiguous spread of tumor or infection. The extradural internal vertebral plexus and paravertebral veins do contain valves (Fig-1e).
1a 1b
Fig. 1-a Fig. 1-b
1c 1d
Fig. 1-c Fig. 1-d
1e
Fig. 1-e