In this chapter, we will address the relevant anatomy, pathogenesis, epidemiology, clinical features, diagnostic testing, specific disorders, rehabilitative management, and prognosis related to radiculopathy and plexopathy.
Each nerve fiber is surrounded by an outer endoneurial sheath. Bundles of nerve fibers are collected into fasciculi, with each fasciculus surrounded by a perineural sheath that provides tensile strength and elasticity to the nerve. Fasciculi are set in areolar connective tissue packing called the epineurium, which protects the nerve from compression (see Fig. 72–1).1
Peripheral nerve connective tissue: Epineurium, perineurium, and endoneurium.(A) The diagram shows the relationships among these three connective tissue layers in large peripheral nerves. The epineurium (E) consists of a dense superficial region and a looser deep region that contains the larger blood vessels.
(B) The micrograph shows a small vein (V) and artery (A) in the deep epineurium (E). Nerve fibers (N) are bundled in fascicles. Each fascicle is surrounded by the perineurium (P), consisting of a few layers of unusual squamous fibroblastic cells that are all joined at the peripheries by tight junctions. The resulting blood-nerve barrier helps regulate the microenvironment inside the fascicle. Axons and Schwann cells are in turn surrounded by a thin layer of endoneurium. (X140; H&E)
(C) As shown here and in the diagram, septa (S) of connective tissue often extend from the perineurium into larger fascicles. The endoneurium (En) and lamellar nature of the perineurium (P) are also shown at this magnification, along with some adjacent epineurium (E). (X200; PT)
(D) Standard error of measurement (SEM) of transverse sections of a large peripheral nerve showing several fascicles, each surrounded by perineurium and packed with endoneurium around the individual myelin sheaths. Each fascicle contains at least one capillary. Endothelial cells of these capillaries are tightly joined as part of the blood-nerve barrier and regulate the kinds of plasma substance released to the endoneurium. Larger blood vessels course through the deep epineurium that fills the space around the perineurium and fascicles. (X450). (Reproduced with permission from Nerve Tissue & the Nervous System. In: Mescher AL, eds. Junqueira's Basic Histology, 14e New York, NY: McGraw-Hill; 2016.)
The dorsal roots carry afferent sensory neurons whose cell bodies reside in the dorsal root ganglion (DRG). The DRG is located in the intervertebral foramen. The ventral roots contain primarily alpha-, beta-, and gamma-type neurons carrying motor outflow from the spinal cord. As they exit the intervertebral foramen, the dorsal and ventral roots join to form the mixed spinal nerve. (Fig. 72–2)
(A) A diagram of the spinal cord ...