Histology of the Transition Zone in Hirschsprung Disease.

Surgical management of Hirschsprung disease requires resection of the aganglionic bowel and transition zone, a length of ganglionic bowel, immediately proximal to the aganglionic segment, with neuropathologic features that seem to correlate with dysmotility. Pathologists must be able to recognize histopathologic features of the transition zone in hematoxylin and eosin-stained sections in order to interpret intraoperative frozen sections and ensure adequate resection. The proximal ganglionic portions of colonic resection specimens from 59 patients with distal aganglionosis were analyzed with closely spaced transverse sections to map the distribution of the 3 most commonly referenced features of transition zone (partial circumferential aganglionosis, myenteric hypoganglionosis, and submucosal nerve hypertrophy). Each of these "primary" findings was restricted to a region ≤5 cm proximal to the aganglionic segment in the overwhelming majority of patients. Exceptions were more common with longer aganglionic segments. Three other neuroanatomic phenotypes (gangliosclerosis, ectopic myenteric ganglia, and eosinophilic ganglionitis) of uncertain clinical significance were distributed more irregularly and often over much longer distances. Routine resection of at least 5 cm of ganglionic bowel proximal to the aganglionic segment may reduce the incidence of transition zone pull-through. However, routine intraoperative frozen section examination of the proximal resection margin to exclude the 3 primary forms of hematoxylin and eosin neuropathology described in this study is strongly advised.