The Pathological Changes in Rats' Nerves Subject to Moderate Compression.

In recent years there has been considerable interest in conditions such as carpal tunnel compression and ulnar neuritis which are believed to be due to gentle compression or constriction of peripheral nerves. Many of these lesions have been explored, and usually the nerve is found swollen proximal to the constriction and narrowed deep to it. Since the symptoms caused by the nerve compression are readily relieved by dividing the constricting agent, there is no opportunity for removing tissue for histological examination ; consequently the pathological changes in the compressed nerves have not been widely studied. In this investigation, because of the lack of suitable human material, lesions resembling those seen in the nerve compression syndromes were induced in rats, and the histology and vascularity of these experimental lesions was examined. REVIEW OF PREVIOUS REPORTS Marie and Foix (1913) described about twenty cases of isolated atrophy of the thenar muscles, which they attributed to compression of the median nerve by the flexor retinaculum. From one patient with severe bilateral muscle wasting, presumably of long standing, they were able to obtain the median nerves at necropsy. They found the nerves swollen and indurated proximal to the retinaculum, the swelling consisting offibrous tissue situated between and within the bundles ofaxons. Dustin (1917) recorded the pathological changes in compressed nerves which had been removed from war casualties. He found that the nerves were swollen not only proximal to the constriction but also distal to it. He ascribed this swelling to an accumulation of fluid secondary to the obstruction of neural lymphatics, which he assumed followed the nerves and drained directly into the cerebrospinal fluid; this accumulation of fluid was followed by intraneural fibrosis. He also found that the constricted nerves were traversed by newly formed arterioles. This is all the human material that has been available for examination, and the lesions studied were much more severe than those generally seen in carpal tunnel syndrome and in related conditions. The more recent investigations concern experimental lesions in warm-blooded animals. seeking a quick and simple technique of repairing cut nerves, tried to splice them with short lengths of tightly fitting arteries. They found that the nerves became swollen proximal and distal to the arterial sheaths. They attributed the proximal swelling to the obstruction of a hypothetical, proximo-distal flow of fluid within the axon, and they ascribed the distal swelling to degenerative changes following division of the …