The peridural membrane of the 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 respo...

The anatomy of the peridural membrane of the human spine

“…The PDM or equivalent structure in other vertebrates (Kappers, 1926) may be of fundamental importance for the homeostasis of the mobile spine, but this and other functions of the membrane (Ansari et al, 2012) are not discussed in this study. However, histological and immunohistochemical characterization of the PDM is presented in an accompanying paper and may provide further insight into the physiology of the membrane (Bosscher, Grozdanov, Warraich, MacDonald, & Day, 2020). Finally, research into the function of the PDM under adverse conditions may improve our understanding of the pathophysiology of the membrane and our ability to treat diseases of the spine.…”

Editorial: Pain 360: Emerging topics in the pathophysiology, diagnosis, and treatment of chronic pain

“…Yet even in the arena of gross anatomy, there remain unanswered questions. Further research into the often-overlooked peridural membrane and its true function represent related areas for further study ( 3 , 4 ). The original research by Bosscher mathematically models the fluid dynamics following pressurized injection into the epidural space.…”