The peridural membrane of the spine has characteristics of synovium.

The peridural membrane (PDM) is a well-defined structure between dura mater and the wall of the spinal canal. The spine may be viewed as a multi-segmented joint, with the epidural cavity and neural foramina as joint spaces and PDM as synovial lining. The objective of this investigation was to determine if PDM has histological characteristics of synovium. Samples of the PDM of the thoraco-lumbar spine were taken from 23 human cadavers and analyzed with conventional light microscopy and confocal microscopy. Results were compared to reports on similar analyses of synovium in the literature. Histological distribution of areolar, fibrous, and adipose connective tissue in PDM was similar to synovium. The PDM has an intima and sub-intima. No basement membrane was identified. CD68, a marker for macrophage-like-synoviocytes, and CD55, a marker for fibroblast-like synoviocytes, were seen in the lining and sub-lining of the PDM. Multifunctional hyaluronan receptor CD44 and hyaluronic acid synthetase 2 marker HAS2 were abundantly present throughout the membrane. Marked presence of CD44, CD55, and HAS2 in the well-developed tunica muscularis of blood vessels and in the body of the PDM suggests a role in the maintenance and lubrication of the epidural cavity and neural foramina. Presence of CD68, CD55, and CD44 suggests a scavenging function and a role in the inflammatory response to noxious stimuli. Thus, the human PDM has histological and immunohistochemical characteristics of synovium. This suggests that the PDM may be important for the homeostasis of the flexible spine and the neural structures it contains

The anatomy of the peridural membrane of the human spine.

A peridural membranous layer exists between the bony wall of the spinal canal and the dura mater, but reports on the anatomy of this structure have been inconsistent. The objective of this study is to give a precise description of the peridural membrane (PDM) and to define it unambiguously as a distinct and unique anatomical entity. Thirty-four cadaveric sections of human thoraco-lumbar spines were dissected. On gross examination, the PDM appears as a smooth hollow tube that covers the bony wall of the spinal canal. An evagination of this tube into the neural foramen contains the exiting spinal nerve. The entire epidural venous plexus, including its extension into the neural foramina, is contained in the body of the PDM. Histological examination of the PDM shows a variable distribution of veins arteries, lymphatics, and nerves embedded in a continuous sheath of fibrous, areolar, and adipose tissue. The posterior longitudinal ligament may be considered a dense condensation of fibrous tissue within the membrane. Thus, the PDM is a unique, continuous, and complete anatomical structure. In the spinal canal, the PDM is adjacent to the periosteum. In the neural foramen, suprapedicular PDM and pedicular periosteum separate anatomically to form a suprapedicular compartment, bounded anteriorly by the intervertebral disc and posteriorly by the facet joint. Trauma or degeneration of the disc or facet joint may lead to inflammation and pain sensitization of PDM. This protective mechanism may be of considerable importance for the functioning of the spine under conditions of strain