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Radiculopathy is probably one of the most frequent types of pain seen in Pain Clinics. Invasive techniques such as transforaminal or translaminar injections are used when other conservative methods have failed. In these procedures, medication such as corticosteroids and local anaesthetics are injected next to the dorsal root ganglion and dorsal nerve root. The decision to use one or another approach depends on factors such as the region to treat (cervical, dorsal or lumbar), the characteristics and the cause of the pain. In this study we review the anatomical and histological aspects that can influence the decision to use each of these techniques for the treatment of radicular pain. We describe the morphology of the intervertebral foramen, its dimensions and the vascular supply of spinal cord and intervertebral foramen. We also analyze ultrastructural details that may help understand the role of spinal nerve root cuffs and other structures such as capillaries and fat that plays an important role on the spread of substances injected in the epidural space and in transforaminal blockade. This review includes a microscopic analysis of the corticosteroids used and in some cases related to the complications published.

The study of the ultrastructure of the spinal arachnoid and its relationship with the spinal nerve roots and dural sac may help explain the different patterns of local anesthetic distribution in the subarachnoid space after spinal anesthesia, as well as some neurological conditions associated with it. Under the electron microscope, the spinal arachnoid matter in humans is composed of two distinct layers: one compact and one trabecular. The trabecular arachnoid, which has a variable thickness, forms tubular structures that enclose each spinal nerve root as well as the spinal cord. The mesh-like structure of the spinal trabecular arachnoid could affect the even distribution of local anesthetics in the dural sac, leading to higher concentrations at certain sites. This anatomical feature would explain, at least in part, some of the neurological manifestations that have been described following spinal anesthesia. In this article, we discuss some of the available literature and present our own experience relevant to the ultrastructure of the spinal arachnoid in humans and its impact on distribution of local anesthetics within the spinal dural sac.

Background Spinal nerve root cuffs may be relevant in selective nerve root and epidural blockade. Methods We examined the ultrastructural aspects of spinal nerve root cuffs, such as their cellular and fibrillar components, using special histological staining methods, transmission and scanning electron microscopy, from six human cadavers. Results The morphology of the spinal nerve root cuff resembles that of the spinal subdural compartment. Cells gather together in compact layers due to specialized junctions. The thickness of its cellular layers is 5 to 8 microns; cells appear oriented parallel to the direction of their own nerve roots. The fibrillar component, made largely of collagen fibers, is found in the outer part of the spinal nerve root cuff and measures 100 to 150 microns. Numerous adipocytes separate dural laminas in concentric layers, extending from the dural sac to the spinal nerve root ganglia. However, adipocytes are not found within the thickness of the dural sac. Conclusions The presence of few capillaries and the short distance between fat and axons may affect the passage of epidurally injected substances towards nerve root axons.

We examined ultrastructural details such as the cellular component and membrane thickness of human spinal pia mater with the aim of determining whether fenestrations are present. We hypothesized that pia mater is not a continuous membrane but, instead, that there are fenestrations across the pial cellular membrane. The lumbar dural sac from 7 fresh human cadavers was removed, and samples from lumbar spinal pia mater were studied by special staining techniques, immunohistochemistry, and transmission and scanning electron microscopy. A pial layer made by flat overlapping cells and subpial tissue was identified. We found fenestrations in samples from human spinal pia mater at the thoracic-lumbar junction, conus medullaris, and nerve root levels, but these fenestrations did not appear at the thoracic level. We speculate whether the presence of fenestrations in human spinal pia mater at the level of the lumbar spinal cord and at the nerve root levels has any influence on the transfer of local anesthetics across this membrane.The ultrastructural anatomy of the human pia mater, such as pial cells, membrane thickness, and subpial tissue at different levels of the thoracic and lumbar spinal cord and nerve roots, was studied by special staining techniques, immunohistochemistry, and transmission and scanning electron microscopy. Fenestrations were found in samples at the thoracic-lumbar junction, conus medullaris, and nerve root levels. No fenestrations were found in samples at the thoracic level. At present, we cannot determine the significance of these findings.

Peripheral nerves transmit electrical signals from the periphery toward the central nervous system and provide motor, secretory or vegetative function. All structures have been reviewed under light microscopy, immunostaining, and different electron microscopic techniques. Details of myelinated, unmyelinated axons, and Schwann cells have been studied. The topographic map of the fascicles has been analysed. These topograms are characteristic and caused by the exchange of axons between different nerve fascicles. This transfer of axons begins in the proximal region of the spinal dorsal root ganglion, close to the epidural space, and continues along the intervertebral canal to distal places. The endoneurium, perineurium and epineurium are layers that cover the peripheral nerves. These three layers of connective tissue are present along the entire length of the nerve, and become thinner as the nerves branch. The endoneurium, perineurium, and epineurium serve different functions with regard to nerve impulse propagation in axons, and protection against infection. The arachnoperineurial transition tissue within nerve root cuffs and the blood nerve barrier in peripheral nerves are discussed, as well as interfascicular tissue and paraneurial compartment.

We describe the findings obtained with the use of the transmission and scanning electron microscopy in the study of human meninges and peripheral nerves. We show details about morphology and distribution of the fibers inside the dural sac. We provide information about the origin of subdural space and structural organization of the arachnoid trabeculates in sleeves that wrap the nervous roots inside the subarachnoid space. We encountered natural fenestrations in the pia mater and studied ultrastructural components of the peripheral nerves coverings. A brief comment on the history of the electron microscopy and the basics of these microscopes complete the presentation of this work. Copyright 2002, Elsevier Science (USA). All rights reserved.

We evaluate the use of the scanning electron microscopy to study different materials used in regional anesthesia with the aim of finding an alternative method for quality analysis of such items. We study spinal needles, epidural catheters, and epidural filters of different manufacturers and we verify differences between products labeled with the same denomination. We find fissures, broken tips, and faults in unused spinal needles. The characteristics of the catheters and microcatheters were observed. We observed structural details from pores in epidural filters and the mechanisms involved in the trapping of particles facilitated by the presence of several numbers of pores randomly distributed in layers within the filtering lamina. Copyright 2002, Elsevier Science (USA). All rights reserved.

Lumbar punctures often are associated with unintentional paresthesias. The tip of the needle in contact with the spinal nerve root initiates depolarization of the axons, which the patient describes as electric shocks in the dermatomes innervated. The paresthesia is triggered by a mechanical stimulus along the axon.

The endoneurium is a fine cylindrical lamina that encloses groups of axons with their respective Schwann cells, creating a specific microenvironment around them. Collagen fibers, which are the main constituent of endoneurium, surround both myelinated and unmyelinated axons. Being permeable, the endoneurium does not interfere with the passage of molecules.

We have previously postulated that it is possible to accidentally insert an epidural needle or catheter into the substance of the dura during attempted epidural block, creating an intradural space. It appears that injection of local anaesthetic into an intradural space leads to an initially inadequate neuraxial block but further doses may produce an extensive life-threatening block. In the laboratory, 54 samples of human thoraco-lumbar dura were obtained from six cadavers and prepared for scanning electron microscopy. Images from these dehydrated specimens were assessed for the presence of spaces within the dura, and attempts were made to insert an epidural catheter, under optical microscopy, into the substance of the dura in 32 cases. Electron microscopy revealed the concentric laminae that compose the dura and the presence of artefactual spaces between some of these. It was possible to insert an epidural catheter into the substance of the dura in eight specimens, creating intradural spaces which remained following catheter removal. If this represents the clinical situation, it may help to explain previously reported cases of atypical neuraxial block and their associated radiological findings.

Background: Although infrequent, subdural block is a complication of epidural anesthesia with obvious implications. Knowledge of the spinal subdural compartment (dura-arachnoid interface) may help elucidate controversies arising from evidence that subdural catheter placement is feasible and may be difficult to identify clinically. Methods: Samples of arachnoid lamina obtained during in vivo lumbosacral surgery (n = 4) and from cadavers (n = 6) were obtained and prepared for transmission electron microscopy and scanning electron microscopy. Subdural spaces were artificially produced in suitable samples, and an epidural catheter was inserted between the arachnoid and dura to compare the dimensions of meninges in relation to epidural catheters. Results: Scanning electron microscopy of the dural sac showed areas of continuity between the arachnoid lamina and dura mater and other parts with both membranes separated by a subdural space. Transmission electron microscopy allowed the study of such border zones, where alternating cellular and collagen layers could be seen. A layer rich in collagen fibers and some fibroblasts separated arachnoid and neurothelial cells (dural border cells). Few specialized membrane junctions were found among cells adjacent to collagen fibers. Dura mater had an average thickness of 260 to 400 μm, with a dural lamina of approximately 4 to 6 μm. In areas where the arachnoid appeared separated from the dural lamina, its thickness measured 35 to 45 μm. Catheters with a diameter of 700 μm were successfully inserted inside the subdural space, between the dura mater and the arachnoid lamina. Conclusions: Dura mater and arachnoid layers act as a single unit but may be pulled apart by traction forces during cadaver processing of the dural sac or in vivo placement of catheters. This generates subdural spaces, either parallel or concentric, because of the minimal resistance offered by the tissue, which may be explained by its few specialized membrane junctions.