Histopathologic findings in patients with idiopathic megacolon: a comparison between dilated and non-dilated loops

Idiopathic megacolon (IMC) is an intractable motility disorder in which chronic symptoms of colonic dysmotility appear with no mechanical cause. Although a pathological analysis is essential to understand the mechanism of IMC, no study has compared the histopathologic findings between dilated and non-dilated loops in IMC cases, and little is known about the proportion of each disease subtype.

Fifty-three full-thickness samples (dilated loops, n = 31; non-dilated loops, n = 22) from 31 IMC cases and 16 samples (dilated loops; n = 8, non-dilated loops; n = 8) from eight controls were collected. All the samples were stained with hematoxylin-eosin (HE), Hu C/D antibody, and CD117 antibody to assess degenerative myopathy, degenerative neuropathy, inflammatory neuropathy, hypoganglionosis, and mesenchymopathy according to the London Classification. Findings of the dilated and non-dilated loop samples were compared, and the proportions of each subtype were analyzed.

Based on a control study, <60 ganglion cells/cm was defined as hypoganglionosis in our series. Myopathy was observed in 11 patients (35.5%), neuropathy was in 19 patients (61.3%), and mesenchymopathy was in 10 patients (32.2%). An overlap between subtypes was observed in some cases. Surprisingly, the non-dilated loop samples exhibited very similar histopathologic abnormalities to those observed in the dilated loop samples in most cases.

Our study is the first to compare the histopathologic findings between dilated and non-dilated loops in IMC patients. Histopathologic abnormalities precede the clinical manifestation of IMC, and may consequently lead to gradual colonic dilatation; however, detailed mechanism including dilation triggering factor needs further elucidation.