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Although neurofibroma frequently occurs as a local manifestation of von Recklinghausen's disease, solitary lesions in the oral and maxillofacial region are rare. Here, we describe an extremely rare solitary neurofibroma that arose in the maxillary sinus of a 41-year-old man. Panoramic radiography and a CT scan showed a slightly swollen maxillary sinus mucosa and a well-circumscribed cystic lesion suggesting a radicular cyst associated with a maxillary molar. The lesions were removed by radical sinusotomy under genera anesthesia. A histopathological examination revealed that the nodular lesion of the sinus mucosa was not encapsulated and that it was composed of somewhat increased numbers of spindle cells accompanied by delicate hyperplastic fibers. These cells had flexed, wavy and linear spindle nuclei. Immunohistochemistry revealed that these tumor cells were positive for S-100 and neuron-specific enolase (NSE). A few spindle cells that were positive for α-SMA within the tumor were thought to be fibroblastic cells (myofibroblasts) derived from the endoneurium or surrounding connective tissue. These findings overall were compatible with the characteristics of neurofibroma. The cystic lesion was diagnosed as a radicular cyst. The patient remained free of tumor recurrence at 26 months of follow-up., Journal of Oral and Maxillofacial Surgery, Medicine, and Pathology, 24(3), pp.171-174; 2012

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.

Male adult Sprague-Dawley rats were subjected to unilateral crush injury, and expression of LPL protein and mRNA were assessed as a function of time post-crush. LPL activity increased in the distal portion of the injured nerve by Day 4 post-crush, after which LPL activity gradually returned to normal levels. Conversely, quantification of LPL mRNA by reverse transcription-polymerase chain reaction demonstrated unchanged or decreased LPL mRNA in the distal nerve. Immunohistochemical analysis of LPL protein expression using an anti-rat LPL antibody revealed that LPL protein is present throughout the endoneurium of the sciatic nerve and increases in abundance following crush injury. The possibility that infiltrating macrophages are responsible for the increase in LPL protein levels in the crush injured nerve was addressed by immunohistochemical staining for ED-1, a differentiated macrophage marker protein. ED-1 was minimally present in the uninjured nerve and was detected at Day 4 post-crush, suggesting that the increase in LPL protein and activity that occurs following crush injury is at least partly derived from macrophages. These data suggest a role for LPL in the response of peripheral nerves to crush injury, possibly in order to facilitate reutilization of lipids from degenerating myelin.—Huey, P. U., K. C. Waugh, J. Etienne, and R. H. Eckel. Lipoprotein lipase is expressed in rat sciatic nerve and regulated in response to crush injury. J. Lipid Res. 2002. 43: 19–25.

A peripheral nerve trunk is composed of nerve fascicles supported in a fibrous collagenous sheath and defined by concentric layers of cells (the perineurium) that separate the contents (the endoneurium) from its fibrous collagen support (the epineurium). In the endoneurium are myelinated and unmyelinated fibers that are axons combined with their supporting Schwann cells to provide physical and electrical connections with end-organs such as muscle fibers and sensory endings. Axons are tubular neuronal extensions with a cytoskeleton of neurotubules and tubulin along which organelles and proteins can travel between the neuronal cell body and the axon terminal. During development some axons enlarge and are covered by a chain of Schwann cells each associated with just one axon. As the axons grow in diameter, the Schwann cells wrap round them to produce a myelin sheath. This consists of many layers of compacted Schwann cell membrane plus some additional proteins. Adjacent myelin segments connect at highly specialized structures, the nodes of Ranvier. Myelin insulates the axon so that the nerve impulse can jump from one node to the next. The region adjacent to the node, the paranodal segment, is the site of myelin terminations on the axolemma. There are connections here between the Schwann cell and the axon via a complex chain of proteins. The Schwann cell cytoplasm in the adjacent segment, the juxtaparanode, contains most of the Schwann cell mitochondria. In addition to the node, continuity of myelin lamellae is broken at intervals along the internode by helical regions of decompaction known as Schmidt−Lanterman incisures; these are seen as paler conical segments in suitably stained microscopical preparations and provide a pathway between the adaxonal and abaxonal cytoplasm. Smaller axons without a myelin sheath conduct very much more slowly and have a more complex relationship with their supporting Schwann cells that has important implications for repair.

The strategy to regenerate nerves across large gaps is to bridge the gap with tissue autografts or biomimetic materials that promote the survival, elongation, and guidance of regenerating axons. The current gold standard is a sensory nerve autograft, such as the sural nerve or saphenous branch of the femoral nerve. The limitations of autografted tissues have prompted a search for biomimetic materials to serve as bridges for gap regeneration of peripheral nerves. Axons that fail to re-enter endoneurial tubes do not synthesize an endoneurium, although they are bundled together in minifascicles by a perineurium. A large number of neuroprotective agents have been tested in animals and humans for their ability to mitigate neuron damage after a spinal cord injury (SCI). The most widely used neuroprotective agent for human SCI has been high-dose methylprednisolone (MP). One of the consequences of SCIs is the spread of damage and disappearance of neurons beyond the immediate area of injury.

Following peripheral nerve injury, cellular and molecular changes at two sites lead to successful regrowth of many axons. In the endoneurium, macrophages are recruited and Schwann cells redifferentiate to produce diffusible and cell surface molecules that support the movement of growth cones, and in nerve cell bodies, changes in gene expression lead to synthesis of growth-associated proteins which are transported to the growth cone to increase its motility. Despite relatively successful axonal regrowth, the degree of functional recovery in many nerves is limited by the lack of cues to guide axons to appropriate targets. Most, if not all, of the spontaneous or therapeutically induced recovery of function, which is commonly seen after injury to the brain or spinal cord, is due to formation or activation of new synaptic connections rather than axonal regeneration.

Axons of both central and peripheral neurons in adult mammals have the intrinsic potential to regenerate after crush or transection, as indicated by the fact that they initiate sprouting after such injuries. A large body of evidence suggests that whether or not axons regenerate depends, in large part, on their associated glial cells. Spinal nerves are organized into three structural levels. The fundamental unit is the endoneurial unit, composed of an axon; its associated Schwann cell sheath; and surrounding connective tissue sheath, the endoneurium. The cell bodies of the motor axons are located in the ventral horn of the cord and synapse with descending tracts of motor axons from the motor centers of the brain. Motor neurons send axons peripherally to join sensory axons distal to dorsal root ganglia. During regeneration, axotomized neurons switch from a transmitting mode to a growth mode and express growth-associated proteins. The distal part of an injured axon is degraded by a process called Wallerian degeneration.

Publisher Summary The incidence and severity of diabetic neuropathy are increased by poor glycemic control, indicating that excess glucose may be the biochemical trigger in the pathogenesis of diabetic neuropathy. The chapter explores that distal symmetrical polyneuropathy is the most commonly recognized form of diabetic neuropathy and is composed primarily of sensory deficits and symptoms, which generally predominate over motor involvement. The symptoms of sensory neuropathy vary depending on the class of nerve fiber involved. The loss of large sensory fibers diminishes light touch, proprioception, and mechanoreception. Loss of small fibers diminishes pain and temperature perception, predisposing to injuries that can lead to diabetic foot ulcers. The pathology of diabetic neuropathy is multifocal with changes in axons, Schwann cells, microvascular elements in the endoneurium, and extracellular matrix. Thus a critical feature of the etiology of neuropathies is the mechanisms by which raised extracellular glucose alters the pattern of gene expression, which constitutes cell phenotype.

Publisher Summary This chapter discusses the structure and function of peripheral nervous system. Peripheral nerves comprise fasciculi of nerve fibers, myelinated and non-myelinated, enclosed in three sheaths of connective tissue. The nerve trunks are surrounded by epineurium, fasciculi by perineurium, and individual nerve fibers by endoneurium. According to axonal diameter and the speed of conduction, nerve fibers may be divided into three main groups: A, B, and C. During development, axons leaving the spinal cord as ventral roots, unite with peripheral processes of dorsal root ganglia to form segmental spinal nerves; they are accompanied at regular intervals by peri-axonal Schwann cells. The chapter discusses the peripheral receptors and effectors. Receptors are transducers, converting mechanical and other stimuli into electrical impulses. They are classified as—superficial exteroceptors responding to external stimuli; deeper proprioceptors stimulated by movement, pressure, and change of body position; and interoceptors from viscera and blood vessels. Somatic effectors are the terminals of myelinated axons of motor neurons that pass without interruption from spinal cord to striated muscle. Visceral effectors are supplied by non-myelinated axons from cells in the autonomic ganglia.

Publisher Summary This chapter reviews the current concepts regarding the connective tissue matrix of the vertebrate peripheral nervous system. The highly vulnerable neural parenchyma is isolated from adjacent tissues by membranous coverings that surround the nervous system. The meninges in the central nervous system and the peripheral sheaths function as biological barriers that maintain the physiological environment and prevent the invasion of the nervous parenchyma by pathogenic agents. Peripheral nerves contain small amounts of glycosaminoglycans, the only two detected in human femoral nerves being dermatan sulfate and heparitin sulfate. Although mature elastic fibers are not present in nerves, elastic-related fibers are frequently observed. The oxytalan fibers are mainly found in the endo- and perineurium whereas the elaunin fibers predominate in the epineurium. Structurally distinct collagen types are also segregated into different compartments of the nerve: Collagen type III is found mainly in the endo- and perineurium whereas collagen type I predominates in the epineurium. The structure of the epi-, peri-, and endoneurium is consistent with the different roles that the supporting connective tissue plays in each of these nerve compartments.

Publisher Summary There is a considerable degree of certainty that most of the labeled phospholipids of the hypoglossal and vagal nerves are present inside the axon. Two groups of experiments substantiate this concept: the first has shown that in the distal part of the crushed nerves, labeled phospholipids are present in the newly regenerating axons; the second one has indicated that in intact nerves, the Schwann cells and the connective tissue cells of the peri- and endoneurium synthesize negligible amounts of 32P-lipids as the cells are only supplied with negligible amounts of 32P either by the blood and lymphatic vessels or by the endoneural space. A series of experiments presented in the chapter reveal various facts: (1) labeled phospholipids flow for long down the axon, (2) the flow per hour becomes constant after four days from labeling the bulb, and (3) labeled phospholipids are continuously synthesized within the confines of the bulb and then conveyed down the axon.