Mesentery
Mesentery | |
---|---|
ileocecal junction | |
Details | |
Pronunciation | /ˈmɛzənˌtɛri/ |
System | Digestive system |
Identifiers | |
Latin | mesenterium |
MeSH | D008643 |
TA98 | A10.1.02.007 |
TA2 | 3740 |
FMA | 7144 |
Anatomical terminology] |
The mesentery is an
The mesocolon was thought to be a fragmented structure, with all named parts—the ascending, transverse, descending, and sigmoid mesocolons, the mesoappendix, and the mesorectum—separately terminating their insertion into the posterior abdominal wall.
Structure
The mesentery of the
The mesentery becomes attached to the colon at the gastrointestinal margin and continues as the several regions of the mesocolon. The parts of the mesocolon take their names from the part of the colon to which they attach. These are the transverse mesocolon attaching to the transverse colon, the sigmoid mesocolon attaching to the sigmoid colon, the mesoappendix attaching to the appendix, and the mesorectum attaching to the upper third of the rectum.
The mesocolon regions were traditionally taught to be separate sections with separate insertions into the posterior abdominal wall. In 2012, the first detailed observational and histological studies of the mesocolon were undertaken and this revealed several new findings.[6] The study included 109 patients undergoing open, elective, total abdominal colectomy. Anatomical observations were recorded during the surgery and on the post-operative specimens.
These studies showed that the mesocolon is continuous from the ileocaecal to the rectosigmoid level. It was also shown that a mesenteric confluence occurs at the ileocaecal and rectosigmoid junctions, as well as at the
Flexural anatomy
Flexural anatomy is frequently described as a difficult area. It is simplified when each flexure is considered as being centered on a mesenteric contiguity. The ileocaecal flexure arises at the point where the ileum is continuous with the caecum around the ileocaecal mesenteric flexure. Similarly, the hepatic flexure is formed between the right mesocolon and transverse mesocolon at the mesenteric confluence. The colonic component of the hepatic flexure is draped around this mesenteric confluence. Furthermore, the splenic flexure is formed by the mesenteric confluence between the transverse and left mesocolon. The colonic component of the splenic flexure occurs lateral to the mesenteric confluence. At every flexure, a continuous peritoneal fold lies outside the colonic/mesocolic complex tethering this to the posterior abdominal wall.[2][6]
Mesocolon regions
The transverse mesocolon is that section of the mesentery attached to the transverse colon that lies between the colic flexures.
The sigmoid mesocolon is that region of the mesentery to which the sigmoid colon is attached at the gastrointestinal mesenteric margin.
The mesoappendix is the portion of the mesentery connecting the
The mesorectum is that part attached to the upper third of the rectum.
Peritoneal folds
Understanding the macroscopic structure of the mesenteric organ meant that associated structures—the peritoneal folds and congenital and omental adhesions—could be better appraised. The small intestinal mesenteric fold occurs where the small intestinal mesentery folds onto the posterior abdominal wall and continues laterally as the right mesocolon. During mobilization of the small intestinal mesentery from the posterior abdominal wall, this fold is incised, allowing access to the interface between the small intestinal mesentery and the retroperitoneum. The fold continues at the inferolateral boundary of the ileocaecal junction and turn cephalad as the right paracolic peritoneal fold. This fold is divided during lateral to medial mobilization, permitting the surgeon to serially lift the right colon and associated mesentery off the underlying fascia and retroperitoneum. At the hepatic flexure, the right lateral peritoneal fold turns and continues medially as the hepatocolic peritoneal fold. Division of the fold in this location permits separation of the colonic component of the hepatic flexure and mesocolon off the retroperitoneum.[2][6]
Interposed between the hepatic and splenic flexures, the greater omentum adheres to the transverse colon along a further band or fold of peritoneum. Dissection through this allows access to the cephalad (top) surface of the transverse mesocolon. Focal adhesions frequently tether the greater omentum to the cephalad aspect of the transverse mesocolon. The left colon is associated with a similar anatomic configuration of peritoneal folds; the splenic peritoneal fold is contiguous with the left lateral paracolic peritoneal fold at the splenic flexure. Division of the latter similarly allows for the separation of the left colon and associated mesentery off the underlying fascia and frees it from the retroperitoneum. The left lateral paracolic peritoneal fold continues distally at the lateral aspect of the mobile component of the mesosigmoid.[2][6]
Microanatomy
Determination of the macroscopic structure of the mesenteric organ allowed a recent characterisation of the histological and electron microscopic properties.
Development
Dorsal mesentery
The
During these topographic changes, the dorsal mesentery undergoes corresponding changes. Most anatomical and embryological textbooks say that after adopting a final position, the ascending and descending mesocolons disappear during embryogenesis. Embryology—An Illustrated Colour Text, "most of the mid-gut retains the original dorsal mesentery, though parts of the duodenum derived from the mid-gut do not. The mesentery associated with the ascending colon and descending colon is resorbed, bringing these parts of the colon into close contact with the body wall."[9] In The Developing Human, the author states, "the mesentery of the ascending colon fuses with the parietal peritoneum on this wall and disappears; consequently the ascending colon also becomes retroperitoneal".[10] To reconcile these differences, several theories of embryologic mesenteric development—including the "regression" and "sliding" theories—have been proposed, but none has been widely accepted.[9][10]
The portion of the dorsal mesentery that attaches to the
Ventral mesentery
The development of the septum transversum takes part in the formation of the diaphragm, while the caudal portion into which the liver grows forms the ventral mesentery. The part of the ventral mesentery that attaches to the stomach is known as the ventral mesogastrium.[11]
The lesser omentum is formed, by a thinning of the mesoderm or ventral mesogastrium, which attaches the stomach and duodenum to the anterior abdominal wall. By the subsequent growth of the liver, this leaf of mesoderm is divided into two parts – the lesser omentum between the stomach and liver, and the falciform and coronary ligaments between the liver and the abdominal wall and diaphragm.[11]
In the adult, the ventral mesentery is the part of the peritoneum closest to the navel.
Clinical significance
Clarifications of the mesenteric anatomy have facilitated a clearer understanding of diseases involving the mesentery, examples of which include
The rationalization of mesenteric and peritoneal fold anatomy permits the surgeon to differentiate both from intraperitoneal adhesions—also called congenital adhesions. These are highly variable among patients and occur in several locations. Congenital adhesions occur between the lateral aspect of the peritoneum overlying the mobile component of the mesosigmoid and the parietal peritoneum in the left iliac fossa. During the lateral to the medial approach of mobilizing of the mesosigmoid, these must be divided first before the peritoneum proper can be accessed. Similarly, focal adhesions occur between the undersurface of the greater omentum and the cephalad aspect of the transverse mesocolon. These can be accessed after dividing the peritoneal fold that links the greater omentum and transverse colon. Adhesions here must be divided to separate the greater omentum off the transverse mesocolon, thus allowing access to the lesser sac proper.[2][14]
Surgery
While the total mesorectal excision (TME) operation has become the surgical gold standard for the management of rectal cancer, this is not so for colon cancer.[2][14] Recently, the surgical principles underpinning TME in rectal cancer have been extrapolated to colonic surgery.[15][16] Total or complete mesocolic excision (CME), use planar surgery and extensive mesenterectomy (high tie) to minimise breach of the mesentery and maximise lymph nodes yield. Application of this T/CME reduces local five-year recurrence rates in colon cancer from 6.5% to 3.6%, while cancer-related five-year survival rates in patients resected for cure increased from 82.1% to 89.1%.[17]
Radiology
Recent radiologic appraisals of the mesenteric organ have been conducted in the context of the contemporary understanding of mesenteric organ anatomy. When this organ is divided into non-flexural and flexural regions, these can readily be differentiated in most patients on CT imaging. Clarification of the radiological appearance of the human mesentery resonates with the suggestions of Dodds and enables a clearer conceptualization of mesenteric derangements in disease states.[18] This is of immediate relevance in the spread of cancer from colon cancer and perforated diverticular disease, and in pancreatitis where fluid collections in the lesser sac dissect the mesocolon from the retroperitoneum and thereby extend distally within the latter.[19]
History
Mesentery has been known for thousands of years, however it was unclear whether mesentery is a single organ or there are several mesenteries.
Almost 10 years before Treves, the Austrian anatomist Carl Toldt described the persistence of all portions of the mesocolon into adulthood.[26] Toldt was professor of anatomy in Prague and Vienna; he published his account of the human mesentery in 1879. Toldt identified a fascial plane between the mesocolon and the underlying retroperitoneum, formed by the fusion of the visceral peritoneum of the mesocolon with the parietal peritoneum of the retroperitoneum; this later became known as Toldt's fascia.[26][27]
In 1942, anatomist Edward Congdon also demonstrated that the right and left mesocolons persisted into adulthood and remained separate from the retroperitoneum—extraretroperitoneal.[28] Radiologist Wylie J. Dodds described this concept in 1986.[18] Dodds extrapolated that unless the mesocolon remained an extraretroperitoneal structure—separate from the retroperitoneum—only then would the radiologic appearance of the mesentery and peritoneal folds be reconciled with actual anatomy.[18]
Descriptions of the mesocolon by Toldt, Congdon, and Dodds have largely been ignored in mainstream literature until recently. A formal appraisal of the mesenteric organ anatomy was conducted in 2012; it echoed the findings of Toldt, Congdon, and Dodds.[6] The single greatest advance in this regard was the identification of the mesenteric organ as being contiguous, as it spans the gastrointestinal tract from duodenojejunal flexure to mesorectal level.[6]
In 2012 it was discovered that the mesentery was a single organ, which precipitated advancement in colon and rectum surgery[29] and in sciences related to anatomy and development.
Etymology
The word "mesentery" and its
Lymphangiology
An improved understanding of mesenteric structure and histology has enabled a formal characterization of mesenteric lymphangiology.[7] Stereologic assessments of the lymphatic vessels demonstrate a rich lymphatic network embedded within the mesenteric connective tissue lattice. On average, vessels occur every 0.14 mm (0.0055 in), and within 0.1 mm (0.0039 in) from the mesocolic surfaces—anterior and posterior. Lymphatic channels have also been identified in Toldt's fascia, though the significance of this is unknown.[7]
See also
- Mesorchium
- Mesovarium
- Blood vessels: The superior mesenteric artery and the inferior mesenteric artery (the two main mesenteric arteries), and the superior mesenteric vein and the inferior mesenteric vein (the two main mesenteric veins), plus their branches and the capillaries
Additional images
-
Mesenteric relation of intestines. Deep dissection. Anterior view.
References
- ^ "Definition of Mesentery". MedicineNet. Retrieved 2018-04-21.
- ^ PMID 23597667.
- S2CID 20276149.
- ^ "Irish surgeon identifies emerging area of medical science". 22 December 2020.
- ^ Beth Mole, The human body may have a new organ—the mesentery (arstechnica.com, 4 January 2017)
- ^ S2CID 205534095.
- ^ S2CID 23266182.
- .
- ^ ISBN 978-0702032257.[page needed]
- ^ ]
- ^ a b Gray's anatomy
- PMID 24264775.
- ^ "Anatomic Problems of the Lower GI Tract". NIDDK. July 2013. Archived from the original on 28 July 2016. Retrieved 3 August 2016.
- ^ S2CID 10393183.
- PMID 18667357.
- S2CID 6464670.
- S2CID 24215331.
- ^ PMID 3490750.
- PMID 20139261.
- Discover Magazine, January 7, 2017
- ^ PMID 20751205.
- ^ Miller, Sara G (January 3, 2017). "Gut Decision: Scientists Identify New Organ in Humans". Live Science.
- ^ PMID 12765932.
- ^ Ellis H. The abdomen and pelvis. In: Ellis H, editor. Clinical anatomy: applied anatomy for students and junior doctors. 12th ed. Blackwell Science; 2010. p. 86.
- ^ McMinn RH (1994). "The gastrointestinal tract". In McMinn RH (ed.). Last's anatomy: regional and applied (9th ed.). London: Langman Group. p. 331e42.
- ^ a b Toldt C (1879). "Bau und wachstumsveranterungen der gekrose des menschlischen darmkanales". Denkschrdmathnaturwissensch. 41: 1–56.
- ^ Toldt C (1919). "Splanchology – general considerations". In Toldt C; Della Rossa A (eds.). An atlas of human anatomy for students and physicians. Vol. 4. New York: Rebman Company. p. 408.
- .
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External links
- Anatomy photo:39:01-0100 at the SUNY Downstate Medical Center
- jejunumileum at The Anatomy Lesson by Wesley Norman (Georgetown University)
- McGill
(Wayback Machine copy)