Lumbar epidural anatomy. A new look by cryomicrotome section.

The anatomic findings from cryomicrotome sections of 38 cadaver lumbar spines are reported. The technique produces high-resolution planar images of undisturbed epidural anatomy. Several observations differ from previous reports that used methods more prone to artifact. The epidural contents are found in circumferentially and metamerically segmented compartments, rather than in a uniform layer. Large areas of the dura are directly in contact with the spinal canal wall. The steeply arched ligamenta flava are fused in the midline to a variable degree. The space anterior to the dura is filled with veins and is isolated from the rest of the epidural space by a membranous lateral extension of the posterior longitudinal ligament. This membrane and a midline posterior fat pedicle are the only observed potential barriers to the spread of epidural solutions. These findings may be important in understanding the mechanics and pharmacokinetics of solutions injected into the epidural space and in refining techniques for needle and catheter placement.