The Peridural Membrane of the Lumbar Spine Has Characteristics of Synovium

Abstract

Recent investigations have renewed interest in a thin well‐innervated peridural membrane PDM which envelopes the contents of the spinal canal and neural foramen in human. Anatomical relations of the PDM in the neural foramen suggest that the suprapedicular compartment of the neural foramen functions as a joint cavity with PDM as its boundary. Inflamed and sensitized PDM may be a source of common low back pain. The purpose of this investigation is to evaluate PDM in the caudal compartment of the neural foramen of the lumbar spine for histological and immunohistochemical (IHC) characteristics of synovium.Dorsolateral and suprapedicular samples of PDM in the lumbar spine of an unembalmed human cadaver were obtained. Samples were evaluated using hematoxylin and eosin staining (HE) and IHC. Four slices of each sample were analyzed (FDNeurotech). Monoclonal and polyclonal antibodies to CD44 (hyaluronan receptor), CD55 (fibroblast like synoviocyte), CD68 (macrophage like synoviocyte) and HAS2 (hyaluronan synthetase 2) were used. Results were evaluated using A1 Nikon confocal immunofluorescent microscopy.HE staining showed a continuous membrane that contains extensive vascular and lymphatic plexus and duct‐like structures, dense and loose fibrous tissue, adipose tissue and nerve tissue in all samples. CD44 was expressed extensively throughout tissues of PDM in all samples, predominantly in perivascular areas but also in adipose, fibrous and nerve tissue. Numerous CD55 positive cells in layer like formations between and around vessels and in the wall of duct‐like structures and in the outer layers of PDM were seen in all samples. CD68 positive cells were found in all samples, but were sparse and mainly found in the outer layer of the membrane. HAS2 positive cells in layer like distributions between vessels or deep to the outer layer of the membrane were found extensively in all samples. Distributions of CD55 and HAS@ positive columnar cells in walls of duct‐like structures and blood vessels were observed in several samples.The results of this study indicate that PDM has histological and IHC characteristics of synovium. IHC identification of CD68 positive cells in the outer layers of PDM and CD55 throughout the membrane, in conjunction with conventional microscopic evaluation of the membrane, suggests the presence of an intima and subintima in PDM similar to synovium. Indeed, PDM histology similar to synovium has been reported by the author and presence of CD44, CD55, CD68 and HAS2 in synovium has been shown by other investigators. No prior reports on the presence of these markers in PDM are available in the literature. Extensive distribution of HAS2 and CD44 in PDM suggests that PDM plays a role in lubrication and homeostasis of the neural foramen and epidural cavity. Presence of CD68, a marker for macrophages, CD55, a receptor involved in regulation of complement activation and CD44, a receptor for metalloproteinases and other inflammatory mediators, indicates that PDM plays an important role in the inflammatory response to tissue injury and pain originating from the spine.Support or Funding InformationTexas Tech University Endowed professorshipThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.