Morphometric analysis of the human superficial radial nerve

The superficial radial nerve (SRN) is one of the cutaneous nerves biopsied for diagnosis of peripheral neuropathy. Morphometric analysis is employed to provide more quantitative data regarding the histomorphology of nerve biopsy. To detect early structural changes, morphometric data from normal nerves are necessary for diagnostic criteria. Unlike the sural nerve, morphometric data on the normal SRN have not been reported. Therefore, a morphometric analysis of the normal human SRN was done in this study. The nerves were harvested bilaterally from 21 fresh human bodies, yielding 34 nerves after excluding damaged ones. Transverse semi-thin sections were analyzed for the number of fascicles, myelinated fiber and axon diameters, myelin sheath thickness, g ratio, density and total number of myelinated fibers using the three-window sampling method. We found that 2-16 fascicles were present. Mean fiber and axon diameters were 6.32 +/- 0.09 (SEM) and 3.44 +/- 0.06 microm, respectively. Average myelin thickness was 1.44 +/- 0.03 microm. Average g ratio was 0.56 +/- 0.01. Mean density of fibers was 8,872.9 +/- 167.4/mm(2). The number of fibers varied from 1,390 to 10,941, with an average of 6,495 +/- 474. These parameters were independent of age. Asymmetry in the number of fibers was also noted in four cases. The data obtained in this study can be applied to histomorphometric evaluations of SRN biopsies, although the possibility of asymmetry should be considered.