Spatial distribution and pattern of extrinsic nerve strands in the aganglionic segment of congenital aganglionosis: stereoscopic analysis in spotting lethal rats.

The distribution and pathways of extrinsic enteric nerves in the aganglionic segment in Hirschsprung's disease have not completely delineated. The zinc iodide-osmic acid method was used to investigate nerve fibers of the intestine in aganglionic rats. A light microscope equipped with a polarizing filter system clarified the major pathways and the fine distribution of extrinsic nerves in the aganglionic segment of a long-segment aganglionic rat model. Two sets of extrinsic nerve strands were observed in the distal aganglionic colon; one consisted of a continuous hypertrophied network located between the longitudinal and circular muscle coats, and the other involved branches that coursed along the blood vessels in the submucosal layer and that originated in the nearby mesentery. These two sets of nerve strands were connected by fine nerve fibers. Hypertrophied myenteric nerve strands were also present in normal (ganglionic) colon, fewer strands were found in the proximal aganglionic colon, and none were found in the ileum. The authors speculate that the ascending extrinsic nerve strands disappear from the ileum in cases of long-segment colonic aganglionosis, by the same mechanism that occurs in normally innervated bowel.