The Human Ileocaecal Junction: An Anatomical Study using Classical and Modern Techniques

Abstract

Introduction As a major site of regulation of the physiological unidirectional flow of gastrointestinal content, the human ileocaecal junction (ICJ) is an important structure for the health of the individual. Although historically it has been considered as a valve, other evidence points to its action as a sphincter. Within the literature, debate continues over the anatomy and action(s) of the ICJ, which prompted further investigation of the anatomy of this discrete region using a combination of established and modern techniques. This is not only important in advancing our understanding of this region but also may assist investigators attempting to devise structures that mimic the actions of the ICJ in patients with distressing symptoms following its surgical removal. The aim of this investigation was to test several hypotheses concerned with the concept that the ICJ is an anatomically specialised region in terms of its musculature, vasculature, nerve supply and distribution of interstitial cells of Cajal (ICCs).

Methods and Materials A total of 27 ileocaecal specimens were obtained for this study (20 cadaver and seven surgical, 12 male, mean age 78 years, age range 49-94 years). Of these, 10 cadaver and five surgical samples were prepared and processed for histology. Surgical samples were also investigated using immunohistochemistry to identify the following antigens: S100 (neural marker), PGP 9.5 (neural marker) and CD117 (a marker for interstitial cells of Cajal). ImageJ was used for quantitative muscle and vascular analyses within histology sections, and for analysis of S100 immunolabelled sections. Observations within the ileal papilla were compared to the adjacent caecum and terminal ileum. Statistical analyses were undertaken using Student’s t-tests, Technical Error of Measurement (TEM) and Intra-class Correlation Coefficient (ICC). Resin injected vascular corrosion casts were produced from two fresh cadaver ICJ specimens. Seven cadaver and one surgical specimen were used to produce ultrathin (1mm) E12 plastinated slices of the junction for qualitative observations and three-dimensional reconstruction. The poor quality of one cadaver and one surgical specimen precluded further analysis.

Results The muscularis externa was thickest at the base of the ileal papilla (4.18 ± 0.4mm), with a gradual increase in thickness in the distal 13mm of the terminal ileum and a gradual tapering towards the tip of the ileal papilla. No secondary muscle thickening was located within the ileal papilla. There was no evidence of increased submucosal vascularity in the ileal papilla compared to the adjacent ileum (p = 0.35) or caecum/colon (p = 0.16) but the inferior lip was more vascular than the superior lip (p = <0.01). The density of S100 immunolabelling was less in the caecum and ileal papilla compared to the terminal one centimetre of ileum (p = <0.01). PGP 9.5 and CD117 positively labelled neuronal and interstitial cells of Cajal within the myenteric plexus, but there was no obvious difference in their density within the ileal papilla compared to the adjacent terminal ileum and caecum. The ICJ was well demonstrated by ultrathin E12 slice plastination enabling the construction of a three-dimensional model of the musculature of the region. The two resin vascular corrosion casts supported the histological observation that the ileal papilla itself was not more vascular than the adjacent terminal ileum but appeared more vascular than the adjacent caecum.

Conclusion In this novel quantitative study of the musculature of the human ICJ, there was evidence of a discrete thickening of the muscularis externa at the base of the papilla consistent with the concept of an anatomical sphincter. There was no anatomical evidence to support a secondary sphincter within the ileal papilla. Neither was there evidence of an increase in vascularity in the ileal papilla or greater density of innervation, contradicting previous suggestions within the literature. These anatomical investigations of the musculature, vascularity, innervation, and distribution of interstitial cells of Cajal within the human ileocaecal junction do not suggest that it is a highly specialised region compared to the adjacent terminal ileum and caecum but are consistent with a sphincteric function. The term ileocaecal valve is misleading and should be replaced by ileocaecal junction.