Histopathological Studies of Chronic Nerve Compression

ABSTRACT

Recently nerve entrapments or nerve root compressions are common clinical symdromes. However, a clear understanding of both pathophysiological and morphological changes is lacking and it may not be completely established in the experimental model for chronic nerve compression, compared with a surprising review of peripheral nerve exposed to various acute damage. Adult Sprague-Dawley rats weighing 250 to 300g were used as the experimental model to elucidate histopathological changes in chronic nerve compression, which were produced by banding the sciatic nerve(normally 1.2mm in diameter) with the length of 1cm silastic tubings with inner diameter, 0.6mm(Group I), 0.9mm(Group II) and 1.5mm(Group III) in each. Specimens were obtained for light and electron microscopic studies postoperatively at 1 and 3 months following by nerve conduction study. Grossly in group I, the sciatic nerve was compressed to approximately 50% of its normal in cuff area and in thin strand on distal part at 1 month and more progressed at 3 months. The sciatic nerve of group II demonstrated 75% of control and distal part in 50% compression at 1 month, but the nerve seemed not to be affected by tubing. Light microscopic findings revealed Wallerian degeneration and diminished large myelinated fiber particularly in the periphery of nerves with 34% of transverse nueral percentage in group I at postoperative 1 month. Above findings were progressed to epineurial scarring and fibrosis at 3 months. There were marked diminution and deformity in large myelinated fiber in group II, but it was not more severe than the ones of group I. Electron microscopic findings in this group revealed the appearance of small regenerating unit clusters and thinly myelinated fibers. In group III, histological findings were not much different from that of normal nerve. Nerve conduction study revealed the decrease in conduction velocity to mean 10 M/sex in group I at 1 month and no electrical conduction at 3 months. In group II, diminution of conduction velocity in 73% of normal range at 1 month was noted, and 82% at 3 months. These findings explain correspondingly the histopathological changes in part of chronic nerve entrapment syndromes and appeal the need of further investigation in this experimental model.