Transmission electron microscopy and histological analysis of the peridural membrane

While first described in 1904, the characterisation of the peridural membrane, which is frequently encountered, yet usually unnoticed, during lumbar decompression surgery, remains inconclusive. This relatively little known membrane is continuous with the posterior longitudinal ligament and lines the epidural space. In this study, we are comparing the membrane and ligamentum flavum from patients to analyse the variations of the histological and ultrastructural compositions. We took samples of the membrane and ligamentum flavum from five separate patients who were undergoing lumbar spine decompression surgery for herniated discs which were then analysed with transmission electron microscopy and stained with H&E (morphology), trichrome (collagen content), and Verhoeff-Van Gieson (elastin content). Upon analysis of the peridural membrane, we observed tightly packed collagen fibres, interspaced with elastin fibres and very few fibroblasts. While the ligamentum flavum showed a significantly higher elastin to collagen ratio and looser arrangement of collagen fibres with a larger extracellular matrix. The peridural membrane was similar in appearance and constituent parts to the dura mater. The peridural membrane is a distinctive and important membrane in the spinal canal, and given its high collagen to elastin ratio and it tightly packed nature, we conclude that it forms a protective layer around the spinal cord which may help in minimising the compressive nature of intervertebral disc herniation.