Mesentery: structure and function
Mesentery study is now possible because of clarification of its structure. Although this area of science is in an early phase, important advances have already been made and opportunities uncovered. For example, distinctive anatomical and functional features have been revealed that justify designation of the mesentery as an organ. Accordingly, it should be subjected to the same investigatory focus that is applied to other organs and systems. In this Review, we summarize the findings of scientific investigations so far and explore its role in human disease.
Introduction
One of the earliest depictions of the mesentery associated with the small bowel and colon was generated by Leonardo DaVinci. The DaVinci finding was continuous and appeared to converge centrally. Over the following four centuries, medical illustrators, surgeons, and physicians drew the mesentery as it appeared, suggesting contiguity. In 1879, Toldt identified a mesentery associated with the ascending and descending colon and showed that, although these structures were flattened against the posterior abdominal wall, they remained separate from it. He did not, however, combine these findings to identify it’s contiguity. Toldt’s findings were highly accurate, but were summarily ignored during the 20th century. Instead, the 1885 findings of Treves were preferred. He concluded that the ascending and descending colon do not normally have an associated mesentery. The resulting depiction in most anatomical, embryological, surgical, and radiological literature of the next century was a fragmented mesentery, present only at the small-intestine, transverse colon, and sigmoid colon. Indeed, some publications continue to depict the presence of a right or left mesocolon as being anomalous.
The mesentery associated with the small intestine and colon is now regarded as contiguous. It emerges from the superior root region and fans out to span the intestine from duodenum to rectum; however, the continuity can be seen only when it is exposed in a certain way. Dividing the peritoneum provides access to a plane formed by the mesentery and underlying fascia. When peeled away from the fascia, it emerges as a discrete entity. Repeating this process from duodenum to rectum reveals it in it’s entirety. Of note, this approach has been used in colorectal resection for many years to permit safe intestinal resection.
Mesenteric contiguity was first demonstrated in an observational cohort study of patients undergoing total mesocolic excision, in which the entire mesocolon is detached from the posterior abdominal wall. Similar observations were made in a cadaveric study of this approach, by the same authors. This contiguity is also apparent in embryological variants, such as non-rotation or malrotation, situsinversus, and mesenteric atresia. Mesenteric, peritoneal, and fascial contiguity were confirmed with datasets available in the Visible Human Project, which provides cross-sectional photographs of human anatomy without alteration and in full colour, with corresponding axial CT images. From these data sets, it was identified in full, enabling development of a radiological atlas of the normal contiguous mesentery against which abnormalities can be compared.
(Prof J C Coffey FRCSI, D P O’Leary PhD)
