The perineurium is composed of connective tissue, which has a distinctly lamellar arrangement consisting of one to several concentric layers. The perineurium is composed of perineurial cells, which are epithelioid myofibroblasts. Perineurial cells are sometimes referred to as myoepithelioid due to their epithelioid and myofibroblastoid properties including tight junctions, gap junctions, external laminae and contractility. The tight junctions provide selective barrier to chemical substances.
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Within motor nerves, each axon is wrapped by the endoneurium, which is a layer of connective tissue that surrounds the myelin sheath. Bundles of axons are called fascicles, which are wrapped in perineurium. All of the fascicles wrapped in the perineurium are wound together and wrapped by a final layer of connective tissue known as the epineurium. These protective tissues defend nerves from injury, pathogens and help to maintain nerve function.
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Perineurial repair involves the individual fascicles and placing sutures through the perineurium, the protective sheath surrounding fascicles, the nerve fibers enclosed by the perineurium. Trauma to the nerve by cutting out each fascicle and fibrosis, a build up of tissue as a reaction, that develops due to the dissections and number of sutures is a problem.Wolford, Larry M., and Eber Stevao. "Considerations in Nerve Repair." BUMC Proceedings 16 (2003): 152-56.
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1163 It is present in the connective tissue of the endoneurium, perineurium, and epineurium.Chen, P., Cescon, M., Megighian, A. and Bonaldo, P. (2014a). Collagen VI regulates peripheral nerve myelination and function.
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This is surrounded by perineurium and epineurium, of which the latter is the outmost layer of dense connective tissue. When it comes to nerve repair, it is crucial that those layers make a good connection.
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The perineurium is a smooth, transparent tubular membrane which may be easily separated from the fibers it encloses. In contrast, the epineurium is a tough and mechanically resistant tissue which is not easily penetrated by a needle.
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Each nerve is composed of a bundle of axons. Each axon is surrounded by the endoneurium connective tissue layer. These axons are bundled into fascicles surrounded by the perineurium connective tissue layer. Multiple fascicles are then surrounded by the epineurium, which is the outermost connective tissue layer of the nerve.
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In third-degree injury, there is a lesion of the endoneurium, but the epineurium and perineurium remain intact. Recovery from a third-degree injury is possible, but surgical intervention may be required. ;Fourth-degree (Class III): Fourth-degree is included within Seddon's Neurotmesis. In fourth-degree injury, only the epineurium remain intact.
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Sporadically, epithelial follicles containing colloidal material can be found. The organ is surrounded by a dense, perineurium-like connective tissue. Originally, the formation was known to embryologists only ("Chievitz Organ") and was considered to be a transient rudimentary structure, disappearing before birth. In 1953, Wolfgang Zenker proved that the formation shows further development and can be found in adult humans with regularity.
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Cross-section of a nerve Each nerve is covered on the outside by a dense sheath of connective tissue, the epineurium. Beneath this is a layer of fat cells, the perineurium, which forms a complete sleeve around a bundle of axons. Perineurial septae extend into the nerve and subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurium.
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Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium. The axons are bundled together into groups called fascicles, and each fascicle is wrapped in a layer of connective tissue called the perineurium. Finally, the entire nerve is wrapped in a layer of connective tissue called the epineurium. In the central nervous system, the analogous structures are known as nerve tracts.
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It has been found by Elmer J. Lund that establishing an artificial electrical field causing a current mimicking the current of injury could facilitate regeneration. This potential for a regeneration therapy was further studied by Robert O. Becker, who described this work in his book The Body Electric. He found that the current of injury runs through the perineurium – through the myelin sheaths of the peripheral nerves.
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Electrically, the nerve shows rapid and complete degeneration, with loss of voluntary motor units. Regeneration of the motor end plates will occur, as long as the endoneural tubules are intact. Axonotmesis involves the interruption of the axon and its covering of myelin but preservation of the connective tissue framework of the nerve (the encapsulating tissue, the epineurium and perineurium, are preserved). Because axonal continuity is lost, Wallerian degeneration occurs.
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Neurotmesis is the most severe lesion with no potential of full recovery. It occurs on severe contusion, stretch, or laceration. The axon and encapsulating connective tissue lose their continuity. The last (extreme) degree of neurotmesis is transsection, but most neurotmetic injuries do not produce gross loss of continuity of the nerve but rather internal disruption of the architecture of the nerve sufficient to involve perineurium and endoneurium as well as axons and their covering.
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805 # Axonotmesis: Involves axonal degeneration, with loss of the relative continuity of the axon and its covering of myelin, but preservation of the connective tissue framework of the nerve (the encapsulating tissue, the epineurium and perineurium, are preserved).Glanze, W.D., Anderson, K.N., & Anderson, L.E (1990), p.117 #Neurotmesis: The most severe form of nerve injury, in which the nerve is completely disrupted by contusion, traction or laceration. Not only the axon, but the encapsulating connective tissue lose their continuity.
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There may be enough neuromas in the body of the lips to produce enlargement and a "blubbery lip" appearance. Similar nodules may be seen on the sclera and eyelids. Histologically, neuromata contain a characteristic adventitious plaque of tissue composed of hyperplastic, interlacing bands of Schwann cells and myelinated fibers overlay the posterior columns of the spinal cord. Mucosal neuromas are made up of nerve cells, often with thickened perineurium, intertwined with one another in a plexiform pattern.
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More mature lesions will react also for EMA, indicating a certain amount of perineurial differentiation. Early lesions, rich in acid mucopolysaccharides, stain positively with alcian blue. When medullary thyroid cancer is present, levels of the hormone calcitonin are elevated in serum and urine. Under the microscope, tumors may closely resemble traumatic neuroma, but the streaming fascicles of mucosal neuroma are usually more uniform and the intertwining nerves of the traumatic neuroma lack the thick perineurium of the mucosal neuroma.
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Axonotmesis of the nerve Axonotmesis is an injury to the peripheral nerve of one of the extremities of the body. The axons and their myelin sheath are damaged in this kind of injury, but the endoneurium, perineurium and epineurium remain intact. Motor and sensory functions distal to the point of injury are completely lost over time leading to Wallerian degeneration due to ischemia, or loss of blood supply. Axonotmesis is usually the result of a more severe crush or contusion than neurapraxia.
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Thus, the overall muscle consists of fibers (cells) that are bundled into fascicles, which are themselves grouped together to form muscles. At each level of bundling, a collagenous membrane surrounds the bundle, and these membranes support muscle function both by resisting passive stretching of the tissue and by distributing forces applied to the muscle. Scattered throughout the muscles are muscle spindles that provide sensory feedback information to the central nervous system. (This grouping structure is analogous to the organization of nerves which uses epineurium, perineurium, and endoneurium).
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The optic nerve is ensheathed in all three meningeal layers (dura, arachnoid, and pia mater) rather than the epineurium, perineurium, and endoneurium found in peripheral nerves. Fiber tracts of the mammalian central nervous system have only limited regenerative capabilities compared to the peripheral nervous system. Therefore, in most mammals, optic nerve damage results in irreversible blindness. The fibers from the retina run along the optic nerve to nine primary visual nuclei in the brain, from which a major relay inputs into the primary visual cortex.
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The endoneurium contains a liquid known as endoneurial fluid, which contains little protein. In the peripheral nervous system the endoneurial fluid is notionally equivalent to cerebro-spinal fluid in the central nervous system. Peripheral nerve injuries commonly release increased amounts of endoneurial fluid into surrounding tissues; these can be detected by magnetic resonance neurography, thereby assisting in locating injuries to peripheral nerves. The endoneurium runs longitudinally along the nerve fiber, but with discontinuities where septa pass inward from the innermost layer of the perineurium.
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Tarlov cysts are most commonly located in the S1 to S4/S5 region of the spinal canal, but can be found along any region of the spine. They usually form on the extradural components of sacrococcygeal nerve roots at the junction of dorsal root ganglion and posterior nerve roots and arise between the endoneurium and perineurium. Occasionally, these cysts are observed in the lumbar and thoracic spine. However, these cysts most commonly arise at the S2 or S3 junction of the dorsal nerve root ganglion.
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Neurotmesis occurs in the peripheral nervous system and most often in the upper-limb (arms), accounting for 73.5% of all peripheral nerve injury cases. Of these cases, the ulnar nerve was most often injured. Peripheral nerves are structured so that the axons are surrounded by most often a myelinated sheath and then an endoneurium. A perineurium surrounds that and the outermost layer is considered the epineurium. When injury occurs, “local vascular trauma leads to hemorrhage and edema (swelling), which results in vigorous inflammatory response resulting in scarring of the injured segment.
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The endoneurium (also called endoneurial channel, endoneurial sheath, endoneurial tube, or Henle's sheath) is a layer of delicate connective tissue around the myelin sheath of each myelinated nerve fiber in the peripheral nervous system. Its component cells are called endoneurial cells. The endoneuria with their enclosed nerve fibers are bundled into groups called nerve fascicles, each fascicle within its own protective sheath called a perineurium. In sufficiently large nerves multiple fascicles, each with its blood supply and fatty tissue, may be bundled within yet another sheath, the epineurium.
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In the peripheral nervous system, the myelin sheath of each axon in a nerve is wrapped in a delicate protective sheath known as the endoneurium. Within the nerve, axons targeting the same anatomical location are bundled together into groups known as fascicles, each surrounded by another protective sheath known as the perineurium. Several fascicles may be in turn bundled together with a blood supply and fatty tissue within yet another sheath, the epineurium. This grouping structure is analogous to the muscular organization system of epimysium, perimysium and endomysium.
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Deep fascia (or investing fascia) is a fascia, a layer of dense connective tissue that can surround individual muscles and groups of muscles to separate into fascial compartments. This fibrous connective tissue interpenetrates and surrounds the muscles, bones, nerves, and blood vessels of the body. It provides connection and communication in the form of aponeuroses, ligaments, tendons, retinacula, joint capsules, and septa. The deep fasciae envelop all bone (periosteum and endosteum); cartilage (perichondrium), and blood vessels (tunica externa) and become specialized in muscles (epimysium, perimysium, and endomysium) and nerves (epineurium, perineurium, and endoneurium).
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Nerves treated in this temperature range experience a disruption of the axon, with Wallerian degeneration occurring distal to the site of injury. The axon and myelin sheath are affected, but all of the connective tissues (endoneurium, perineurium, and epineurium) remain intact. Following Wallerian degeneration, the axon regenerates along the original nerve path at a rate of approximately 1–2 mm per day. Cryoneurolysis differs from cryoablation in that cryoablation treatments utilize liquid nitrogen (boiling point of -195.8 °C) as the coolant, and therefore, fall into the range of a neurotmesis injury, or 3rd degree injury according to the Sunderland classification.
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The most extreme degree of neurotmesis is transsection, although most neurotmetic injuries do not produce gross loss of continuity of the nerve but rather, internal disruption of the nerve architecture sufficient to involve perineurium and endoneurium as well as axons and their covering. It requires surgery, with unpredictable recovery.Glanze, W.D., Anderson, K.N., & Anderson, L.E (1990), p.810 A more recent and commonly used system described by the late Sir Sydney Sunderland, divides nerve injuries into five degrees: first degree or neurapraxia, following on from Seddon, in which the insulation around the nerve called myelin is damaged but the nerve itself is spared, and second through fifth degree, which denotes increasing severity of injury.
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There are several hypotheses proposed regarding the formation of Tarlov cysts, including: hemorrhagic infiltration of spinal tissue, inflammation within the nerve root cysts followed by inoculation of fluids, developmental or congenital origin, arachnoidal proliferation along and around the exiting sacral nerve root, and breakage of venous drainage in the perineuria and epineurium secondary to hemosiderin deposition after trauma. Tarlov himself theorized that the perineural cysts form as a result of blockage of venous drainage in the perineurium and epineurium secondary to hemosiderin deposition, after local trauma. Another theory gaining increasing popularity, over the past decade, is one postulated by Fortuna et al.; it described perineural cysts to be the results of congenital arachnoidal proliferation along the exiting sacral nerve roots.
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