The human ileocaecal junction: anatomical evidence of a sphincter

The human ileocaecal junction (ICJ) is a major transition zone regulating intestinal transit. Historically, it has often been considered a valve rather than a sphincter. The microscopic anatomy of this junction was studied searching for evidence of an anatomical sphincter and neuromuscular specialisation.

Ileocaecal specimens were obtained from ten cadavers and five surgical donors (7 male, mean age 81 years, age range 68-94) and examined by histology and immunohistochemistry. Quantitative analyses of muscle thickness and submucosal vascularity were performed together with immunohistochemical studies of innervation and the distribution of interstitial cells of Cajal.

The thickness of the muscular layer in both the ileum and the colon increased significantly over a distance of 1 cm leading up to the base of the ileal papilla where it reached a maximum (4.19 ± 2.0 mm) before gradually tapering towards the tip of the papilla. Submucosal vascularity in the ileal papilla was not increased compared to the adjacent ileum or caecum/colon. Neuronal density was less in the caecum and ileal papilla compared to the terminal ileum (P < 0.05). Interstitial cells of Cajal were identified within the myenteric plexus of the ICJ but their density was similar to the adjacent bowel.

A localised muscle thickening at the base of the ileal papilla is consistent with an intrinsic anatomical sphincter. There was no evidence that the ICJ has increased submucosal vascularity or a greater density of innervation compared to the adjacent bowel. The term ileocaecal valve is misleading and should be replaced by ileocaecal junction.