How the mesentery became your 79th organ

The researcher behind the discovery reveals how he made it, and what it means for medicine.

The world’s anatomy books will need some updating—a new organ has been discovered, meaning we now have 79, not 78. The designation of the mesentery as an organ made waves this month, even resulting in an update to Gray’s Anatomy. The mesentery was previously believed to consist of fragmented and separate parts, but it became clear to John Calvin Coffey and his colleagues that it’s one continuous organ, something with a unique function we can’t survive without. We speak with him about how he made the realization and what his discovery means for medicine.

To learn more about how Coffey’s work will affect research in Crohn’s disease, follow his project on ResearchGate.

ResearchGate: What was the previous view on the mesentery?

John Calvin Coffey: The classic anatomic view was that it was made of multiple separate parts. This not only led to great confusion and a lack of clarity, but it also meant people tended to ignore the mesentery and not focus research efforts on it.

According to the classic view, the small intestine, transverse colon, and sigmoid colon all have a mesentery. However, the right and left colon do not. If a mesentery was found in these regions of the colon, it was regarded as anomalous, or pathological.

The erroneous description of the mesentery meant that surgeons tended to focus almost entirely on the intestinal component when removing an organ, almost to the exclusion of the mesentery. In addition, radiologists examining CT or MRI images of the abdomen always struggled, and indeed reported their struggles in the literature, to reconcile what they were seeing on radiological scans with the classic view of mesentery anatomy.

J. Calvin Coffey, professor of surgery and deputy director of the Graduate Entry Medical School, University of Limerick, Ireland and Consultant Surgeon, Health Services Executive. Picture: Alan Place.

RG: What motivated your research into it?

Coffey: I am primarily a colorectal surgeon, and I noticed that when we conduct good colorectal surgery, we always access the plane formed between the mesentery and the back wall of the abdomen. We then detach the mesentery from this plane and, as the intestine is attached to the mesentery, the intestine becomes mobile enough for us to remove. Surgeons rely on the presence of the mesentery throughout.

RG: When did you first realize that this could be a distinct organ?

Coffey: This was a gradual realization. As we accumulated data regarding structure, ultrastructure, and function it became apparent to us that we had the basis to argue that the mesentery is as an organ. The research started in 2008 whilst I was in surgical training and has continued up to this day.

RG: How did you go about proving this?

Coffey: We accumulated evidence relating to structure and function. We also accumulated evidence in disease settings where the mesentery was abnormal, and we were able to say that the mesentery performs an essential or vital function. The studies involved a strong collaboration between surgeon and anatomist. Many of the studies conducted were completed in cadavers. As I am a surgeon, every operative case was an opportunity to accumulate and document observations related to the mesentery. I also have the advantage of seeing cases of mesenteric abnormalities and thus was able to study the shape and the function of the mesentery in these settings also.

RG: How does something officially become a new organ?

Coffey: No single authority formalizes the adoption of a structure as an organ. In the absence of such a body, one must look at all the definitions of the word “organ” and see if one’s argument holds true. We have done this with the mesentery and found that it fulfils all the criteria that are interchangeably adopted in defining an organ. It is a discrete anatomic entity. One cannot survive without it, and so it provides a vital function. It has many unique cellular and tissue-based adaptations that are crucial to it being able to perform its function. Given these properties, and given that it is discrete, substantive, unique, and vital, then there is a strong argument for it being an organ.

RG: And how does it feel to have made this distinction? What about the changes in anatomy being included in the new edition of Gray’s Anatomy?

Coffey: We are thrilled to have clarified the structure and for Gray’s Anatomy to have been updated to reflect continuity of the mesentery from the duodenum to the rectum. We are most proud of the fact that by clarifying the structure, the mesentery can now be studied using scientific methodology.

We were also thrilled that the review article was published in such a prestigious journal such has the Lancet Gastroenterology and Hepatology.

Drawing of mesenteric organ by Leonardo Da Vinci.

RG: What does this discovery mean for treatment and diagnostics?

Coffey: This means that our knowledge of human biology in health and disease is going to expand considerably, and we are enormously proud of that achievement. Clarification of mesenteric anatomy has provided the clinical community with a new perspective with which to view abdominal diseases such as Crohn’s disease, volvulus, malrotation and many others. For example, if gastroenterologists are able to identify the mesentery at colonoscopy using ultrasound, they can follow its trajectory and minimize the pain and discomfort that patients experience during colonoscopy.

In relation to Crohn’s disease, even Crohn himself recognized the importance of the mesentery here. Early data indicate that it plays a more important role than we previously thought. The mesentery is used by inflammatory cells which track across it to reach the surface of the intestine and exert their pro-inflammatory effects.

RG: What’s next for your research?

Coffey: I think that scientists and clinicians are at a very exciting point in time. We can develop the science of the mesentery, because we can now systematically study it in the way we have been able to study other organs.  There are many areas to explore. For example, the mesentery must intersect with the intestine to be attached to it. This intersection is at least two meters long and has not yet been investigated, despite the fact that it must be one of the most important anatomic zones in the digestive system.

Increases in abdominal fat are linked to heart disease, stroke, metabolic syndrome, diabetes, peripheral vascular, and many other diseases. We now know, as a result of the recent clarification of mesenteric anatomy, that the fat within the mesentery is the single largest contributor to abdominal fat. Early data also indicate that if part of the mesentery is removed in Crohn’s disease, that recurrences necessitating further surgery, are reduced.

Clarification of mesenteric structure has implications for surgeons, gastroenterologists, radiologists, pathologists, oncologists and many other clinical specialties.

It also has implications for scientists involved in the investigation of the immune system, human metabolism, anatomy, embryology, histology and many other scientific disciplines. With the platform that we now have, I think we will see an expansion in many of these fields of scientific and clinical endeavor.