Radiologic, Histologic and Scanning Electron Microscopic Characterization of the Peritoneal Reflection in Crohn's Disease

The peritoneal reflection bridges visceral and parietal peritoneum and lacks adjoining or underlying organs. As such it provides an opportunity to perform a focussed examination of the peritoneum in Crohn's disease. The aim of this study was to exploit this anatomical property and conduct a multilayered, focussed examination of the peritoneal reflection in normality and in Crohn's disease. The in vivo reflection was first digitally reconstructed using computerized tomographic imaging of the abdomen, in normal subjects (n = 20) and in patients with Crohn's disease (n = 20). Pixel density in both sets of digital replica was determined and compared. Separately, the reflection was harvested from ten cadavers (normal controls) and from ten patients with intestinal Crohn's disease. Samples were processed for histological and scanning electron microscopic (SEM) analysis. Sections were evaluated qualitatively and quantitatively to assess composition and organization of the reflection in normality and in Crohn's disease. The average pixel density of the peritoneal reflection was increased in Crohn's disease compared with controls (4 ± 32 vs. -86 ± 24, p < 0.005). At the histological level, the reflection in Crohn's disease was thicker than in normality (0.410 ± 0.089 mm vs. 0.219 ± 0.048 mm, p = 0.005). This was partly explained by a greater number of cells (90 ± 28 vs. 47 ± 22, p = 0.002), and vessels (3 ± 1.3 vs. 1.7 ± 1.3 respectively, p = 0.037), per high powered field, in the reflection in Crohn's disease. The SEM analysis demonstrated the cellular infiltrates apparent in Crohn's disease were acute inflammatory in nature and were widespread both on the surface and within, the reflection. The SEM analysis identified a pattern of looping channels in the mesothelium in Crohn's disease. This mesothelial signature was absent in normality. The channels of the network were topographically associated with tubular structures which were inverse in shape to the channels, but similar in dimension. The peritoneal reflection is a site of acute inflammation in Crohn's disease. Crohn's disease is associated with a mesothelial signature characterized by a network of looping channels.