Circumferential distribution of ganglion cells in the transition zone of children with Hirschsprung disease.

We prospectively studied the circumferential distribution of ganglion cells in the transition zone from a study population of 21 patients with Hirschsprung disease (HD) undergoing a pull-through procedure over a 26-month period. Twelve cases were satisfactory for examination, in that the transition zone was contained within a single surgical specimen and specimen distortion was minimal. Ganglion cells in the submucosa were counted in all 12 cases. In seven of the cases, the transition zone was proximal to the rectal sleeve and myenteric plexus ganglion cells were also counted. We found an uneven circumferential distribution of ganglion cells in both myenteric plexus and submucosa of the transition zone, resulting in a "leading edge" of ganglion cells extending into aganglionic distal bowel. The maximum length of this leading edge was 2.4 cm and 2.1 cm in the myenteric plexus and submucosa, respectively. Ganglion cells at the tip of the leading edge were present in clusters of up to six ganglion cells, in marked contrast to an absence of ganglion cells for most of the remainder of the circumference. Closely spaced myenteric plexus ganglia were seen at the tip of the leading edge in some cases. The leading edge was more frequently observed along the antimesenteric side, but this was not statistically significant. Our findings have relevance in the interpretation of intraoperative biopsies at the time of pull-through surgery and subsequent biopsies of neorectum in patients with surgically corrected HD.