ABSTRACT
Grossly, the sural nerve looks like a pearly white cord and measures 2 to 3 mm in diameter. Thus, it resembles angel-hair pasta. It is usually adhered to some loose adipose tissue. In general, the superficial peroneal and radial nerves are smaller than the sural nerve in diameter. There are three compartments in the nerve: the epineurium, perineurium, and endoneurium. Five to fifteen nerve fascicles are usually present in the sural nerve (Color Figure 4.1),* surrounded and bound by connective tissue in the epineurium (Color Figures 4.2 and 4.3). The epineurium makes up approximately one-half of the cross-section area of the nerve. The most important structures in the epineurium are arterioles and venules because these are the vessels most often involved in vasculitic neuropathy. One or two arterioles are found in the epineurium, and their diameters range from 30 to 300 µm. Pacinian corpuscles are rarely observed in the epineurium. Midroni et al. observed this in only 3 of nearly 700 consecutive cases. Apparently, a few mononuclear cell infiltrates were found around the vessels in the epineurium of normal nerves.1,2 Dyck stated that it is not always easy to decide whether the degree of perivascular infiltration is abnormal.1 Again, one has to judge such findings in correlation with the clinical findings. Other cell types normally seen in the epineurium include fibroblasts and mast cells. The perineurium separates the endoneurium of the nerve fascicle from the epineurium. The endoneurium contains nerve fibers, Schwann cells, and blood vessels, together with bundles of endoneurial collagen fibers oriented longitudinally along the nerve fascicles. Ninety percent of the cell nuclei in the endoneurium belong to Schwann cells; the rest of the cells are mainly fibroblasts and capillary endothelium. Occasional mast cells are also present in the endoneurium. A regular light microscope does not reliably detect and identify scattered lymphocytes in normal nerves. Thus, if scattered lymphocytes are definitely observed under the light microscope, this should be interpreted as abnormal. A few recent studies have found a few leukocytes in normal nerves using Leukocyte Common Antigen (LCA) immunohistochemical staining.3,4 There were no immunopositive T-or Bcells.5 As a practical guideline, Midroni stated that a few (three to four on cross-section) LCA-positive cells randomly dispersed throughout the endoneurium of an average fascicle do not necessarily indicate abnormality.2 However, cuffing around an endoneurial vessel is always regarded as a significant marker of inflammation.
