Transmission electron microscopy and histological analysis of the peridural membrane.

INTRODUCTION: 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. MATERIALS AND METHODS: 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). RESULTS: 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. CONCLUSION: 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.

The Peridural Membrane of the Human Spine is Well Innervated.

There is evidence that low back pain may originate from a peridural membrane (PDM) at the inferior and medial aspect of neural foramen of the lumbar spine. The objective of this investigation was to determine if this membrane contains neural elements suggestive of sensory innervation with nociceptive function. Spines of four embalmed and three non-embalmed human cadavers were dissected using a sagittal approach to the neural foramen. Seventeen samples of the peridural membrane overlying the neural foramen were collected for immunohistochemistry (IHC) examination by light microscopy and transmission electron microscopy (TEM). Chromagin tagged antibodies to protein gene product 9.5 (PGP9.5) and S-100, and fluorescent antibodies to substance P and calcitonin gene related peptide (CGRP) were used to label neural structures in tissue sections cut from paraffin embedded blocks. This approach allows good visualization of all neural elements, small sensory, and nociceptive nerve fibers in particular. Neural elements were found in all samples. Marked presence of small nerve fibers was observed in 12 of 15 samples. IHC and TEM evaluation revealed myelinated as well as unmyelinated fibers in the peridural membrane. CGRP and substance P immunoreactive fibers indicative of nociceptive function were abundant. These findings confirm and expand evidence that the peridural membrane in human is well innervated and contains sensory nociceptive nerve fibers suggestive of a nociceptive function of the membrane.

Clinical implications of epidural fat in the spinal canal. A scanning electron microscopic study.

BACKGROUND AND OBJECTIVES: This review of articles summarizes recent developments in relation to fat located in the epidural space and also in dural sleeves of spinal nerve roots in order to improve our understanding of the clinical effects of the epidural blockade. METHOD: Medline search was carried cross-matching of the following words: "epidural fat", "epidural space", "adipose tissue" and "fat cells" from 1966 to 2008 in which articles referring to different pathologies that alter the epidural fat were also reviewed. Techniques used by different authors included the use of samples from dissections, cryomicrotome sections, as well as light and electron microscopy. RESULTS: Fat in the epidural space has a metameric distribution along the spinal canal that can be altered in some pathological conditions. Epidural fat is not evenly distributed. At cervical level fat is absent while in the lumbar region, fat in the anterior and posterior aspects of the epidural space forms two unconnected structures. Fat cells are found also in the thickness of dural sleeves enveloping spinal nerve roots but not in the region of the dural sac. Epidural lipomatosis is characterized by an increase in epidural fat content. When a patient has a combination of kyphosis and scoliosis of the spine, the epidural fat distributes asymmetrically. Spinal stenosis is frequently accompanied by a reduction in the amount of epidural fat around the stenotic area. CONCLUSIONS: The epidural space contains abundant epidural fat that distributes along the spinal canal in a predictable pattern. Fat cells are also abundant in the dura that forms the sleeves around spinal nerve roots but they are not embedded within the laminas that form the dura mater of the dural sac. Drugs stored in fat, inside dural sleeves, could have a greater impact on nerve roots than drugs stored in epidural fat, given that the concentration of fat is proportionally higher inside nerve root sleeves than in the epidural space, and that the distance between nerves and fat is shorter. Similarly, changes in fat content and distribution caused by different pathologies may alter the absorption and distribution of drugs injected in the epidural space.

Determination of the optimal angle for needle insertion during caudal block in children using ultrasound imaging.

Using ultrasound imaging, the optimal angle for needle insertion during caudal epidural injection in children was estimated. After general anaesthesia, ultrasonography was performed at the sacral hiatus in 130 children aged 2-84 months positioned in the lateral position. The median [range] values for the intercornual, caudal space depth and the distance from skin to the posterior sacral bony surface were 17.0 [9.6-24] mm, 3.5 [1-8] mm and 21.0 [10-39] mm, respectively. The optimal angle showed no significant correlation with age, weight, height or body surface area. The median [range] calculated optimal angle for the needle was 21.0 [10-38] degrees. We conclude that the needle should be inserted at about 20 degrees to the skin to avoid puncture of the bone and potential intra-osseous injection.

[New results in the visualization of the spinal dura mater with scanning electron microscopy]. / Neue Ergebnisse bei der Darstellung der Dura mater spinalis mittels Rasterelektronenmikroskopie.

UNLABELLED: Although there are various published descriptions of the dura mater spinalis [4, 7, 9, 11, 16], some points relating to the texture of the collagen fibres in the dura have still not been adequately explained. In this study the orientation of the collagen fibril bundles was revealed with the aid of scanning electron microscopy, and our observations have yielded new insights into the three-dimensional structure of the human dura mater spinalis. MATERIALS AND METHODS: The preparations used were taken from the bodies of four persons who had died of acute cardiac infarct at the ages of 70-78 years. The histories of these patients gave no indications of earlier neurological, endocrine or septic illnesses. The tissue examined was taken 8-12 h after death in all cases; it was immediately fixed in glutaraldehyde and then processed for scanning electron microscopy in the usual way. RESULTS: In the outermost (epidural) layer of the dura mater spinalis the collagen fibres are bunched together in bands that run in all directions. Elastic fibres 2 mm thick are woven into this three-dimensional network of collagen systems. On the inside (the arachnoid side) thin collagen fibres are fused into layers in such a way that the innermost layer resting on the arachnoid has a smooth, shiny appearance comparable to that of a serosa. It is attached to the actual dura with a supporting band of connective tissue. Rests of the subdural neuroepithelium could contribute to the smooth appearance of the superficial aspect. CONCLUSIONS: The outermost layer of the dura is made up mainly of collagen fibres, which run in all three directions--longitudinal, horizontal and transverse--both singly and in groups. These findings are at odds with "classic" descriptions, according to which the fibres in the dura mater spinalis all have a parallel course with a longitudinal orientation in tangential sections.

[Angio-fibrolipoma in epidural space of the vertebral canal]. / Naczyniako-wlókniako-tluszczak w przestrzeni zewnatrzoponowej kanalu kregowego.

55-yera old patient with angio-fibro-lipoma of thoracic part of the vertebral canal was described. This rare, benign tumour was totally removed. Subsequently the neurological state of the patient improved.

Gd-DTPA enhancement of posterior epidural scar: an experimental model.

Because of the tremendous clinical and physiological importance of anterior epidural scar, an easily produced and reproducible model to assess potential pathways for lessening its formation is a necessity. We speculated whether posterior epidural scar (produced by the less complex surgery of laminectomy alone) could be considered equivalent to anterior scar from an imaging standpoint; that is, enhancement following Gd-DTPA irrespective of scar age. Posterior epidural scar in dogs showed the highest degree of enhancement 1 month after surgery, with a rapid decline thereafter out to 4 months postsurgery to a level equivalent to that of paraspinal muscle. Gd-153-DTPA time/activity curves paralleled the Gd-DTPA findings. Light microscopy showed granulation tissue after 1 month, and mature scar with large amounts of collagen 4 months after surgery. Electron microscopy showed tight capillary endothelial junctions. An appropriate model for epidural scar, which has imaging characteristics similar to human anterior scar, necessitates an extensive lumbar laminectomy with anterior epidural dissection. A simple laminectomy, while easily performed, does not provide a physiologically correct time course of enhancement.

Gadolinium-DTPA-enhanced MR imaging of the postoperative lumbar spine: time course and mechanism of enhancement.

To define the time course and mechanism of enhancement of epidural fibrosis after gadolinium-DTPA (Gd-DTPA) injection, we undertook a three-part study in humans and dogs with epidural scar after spine surgery. First, the dynamic in vivo contrast-enhancing properties of epidural scar were assessed by using sequential fast (18-sec) spin-echo sequences after contrast injection. Epidural scar in dogs rapidly enhanced; peak enhancement (101%) was 6 min after injection, with a slower decline toward baseline to 45% after 44 min. Epidural fibrosis in patients followed a similar pattern, with a maximum enhancement of 73% after 5 min. Paraspinal muscle had a lower peak enhancement in both patients (36%) and dogs (22%). Second, vascular injection in two dogs with India ink demonstrated multiple small vessels throughout the epidural scar. Third, light and electron microscopy was performed on epidural scar obtained at reoperation in both patients and dogs. Light microscopy showed multiple small capillaries scattered throughout a background of collagen. Electron microscopy demonstrated a wide variation in the junctions between endothelial cells ranging from "tight" to "loose." Regions of endothelial discontinuity were also visualized. This study suggests that Gd-DTPA diffuses rapidly into the extravascular space in epidural scar, with a slower, net movement toward the intravascular compartment as the agent is renally filtered. The contrast agent transgresses the endothelium through "leaky" intercellular junctions and areas of endothelial discontinuity.