Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Peritoneum, mesentery and peritoneal cavity
Core Procedures
All operations can be performed via open, laparoscopic or robotic approaches and therefore the approach is not specified.
-
Stomach: total gastrectomy, partial gastrectomy
-
Pancreas: subtotal pancreatectomy, pancreaticoduodenectomy
-
Liver: hepatectomy
-
Spleen: splenectomy
-
Appendix: appendicectomy
-
Colon: complete mesocolic excision, total mesocolic excision, partial mesocolic excision (left or sigmoid)
-
Rectum: total mesorectal excision (TME), partial mesorectal excision, Hartmann's procedure, transanal total mesorectal excision (TaTME)
-
Repair of malrotation: restoration of mesenteric conformation and pexy for non-rotation
Most intestinal, hepatic, pancreatic and splenic operations are technically based on mesenteric and peritoneal anatomy. The classical appraisal of mesenteric and peritoneal anatomy was founded on the concept of multiple ‘mesenteries’ and has recently been challenged on the grounds that the mesentery is a single and continuous organ. Although the current anatomical model is relatively new, it is evidence-based and universally applicable (even in the setting of congenital abnormalities). It is the anatomical foundation of digestive system surgery distal to the oesophagus. All aspects of mesenteric, peritoneal and fascial anatomy cannot be covered in this chapter; the reader is referred to Mesenteric Principles of Gastrointestinal Surgery: Basic and Applied Science for a comprehensive description.
Definitions
As the peritoneum, mesentery and associated fascia are continuous, there are no distinctive landmarks to indicate the anatomical limits of adjacent regions. Notwithstanding, a nomenclature has developed with reference to each different region. The terms of this nomenclature are categorized as anatomical, surgical and embryological in what follows and are defined and explained in Table 57.1 .
TABLE 57.1
Anatomical terminology defined and explained
| Term | Definition | Explanation |
|---|---|---|
| Mesentery | The collection of tissues that maintains abdominal digestive system organs in position and in continuity with other systems | It is important to draw attention to a number of aspects of this definition: Unlike previous definitions, the words ‘fold’, ‘membrane’ and ‘sheet’ are not used: once the mesentery has been mobilized or detached, it loses the shape it had in situ Earlier descriptions of the mesentery described it connecting the intestine to the posterior abdominal wall. It is more accurate anatomically to consider the mesentery as maintaining connectivity between abdominal digestive system organs and systems of the body, rather than maintaining ‘direct’ continuity with the posterior abdominal wall. The mesentery is attached to the posterior abdominal wall through a number of anatomical mechanisms, including the apposition of mesenteric regions, the peritoneal bridge or reflection, and vascular, neurological and lymphatic connections Previous definitions describing the mesentery as a double fold of peritoneum have been omitted from the current definition. It is correct to say that the surface of the mesentery is mesothelial and in continuity with the peritoneum. However, the mesentery has a substantive stroma that increases in volume with age and is the anatomical correlate for many mesenteric functions. It is misleading to highlight one histological element among several |
| Peritoneum | A continuous serous membrane supported by connective tissue, lining the innermost surface of the abdominal wall, from which it is reflected on to viscera where it is continuous with surface mesothelium ( Fig. 57.2 ; see Fig. 57.1B ) | The word ‘reflected’ refers to where the peritoneum leaves the abdominal wall to reach and merge with the surface of an adjacent viscus (such as the intestine, mesentery, liver or spleen). Where the peritoneum is reflected on to the mesentery, it is continuous with the mesothelial surface of the mesentery. Collectively, regions of the peritoneum form a mesothelial canopy that assists in maintaining the position of viscera within the abdomen. This is of considerable surgical importance, as the peritoneum obscures certain regions of the mesentery (and related structures) from direct visualization. As a result, it must be sharply incised to provide surgical access to mesentery and fascia. The peritoneum is of considerable pathological and radiological relevance because it also forms a barrier to the spread of disease |
| Fascia (Toldt's) | A connective tissue layer between an organ and retroperitoneum, where these are contiguous | Organs apposed to the retroperitoneum include the liver (at the bare area), duodenum, pancreas, mesentery and intestine (at several levels) |
| Spaces and fossae | There are several spaces and fossae that are of historical but are not of surgical relevance | |
| Peritoneal reflection | Peritoneum bridging contiguous organs (see Figs 57.1B , 57.2 ) | |
| Peritoneal folds | A fold occurs where the peritoneum doubles back sharply on itself | These occur at points where the intestine and mesentery undergo a marked conformational change (such as at duodenojejunal, ileocaecal and splenic flexures). Other than serving as landmarks, they are of limited surgical relevance |
| Mesoduodenum | Mesentery attached to the duodenum, located posterior to the pancreas and anterior to the posterior abdominal wall | In the adult, the mesoduodenum is located posterior to the head and body of the pancreas and narrows in all planes as it proceeds distally. It is continuous with the dorsal mesogastrium superiorly and with the mesenteric root region (see later) distally |
| Falciform ‘ligament’ | The most anterior region of ventral mesogastrium located between the anterior surface of the liver and the anterior abdominal wall | It is a region of mesentery and not a ligament |
| Mesocolon | Mesentery associated with colon | The mesocolon is a continuation of the small intestinal mesentery and is arbitrarily divisible into regions, according to the region of associated intestine. These include the right, transverse and left mesocolon, the mesosigmoid and the mesorectum. The mesosigmoid is further divided into two regions (medial and lateral), which can be differentiated by the fact that the medial region of the mesosigmoid is apposed to (or flattened against) the retroperitoneum, while the lateral region is mobile |
| Meso-appendix | Mesentery associated with the appendix | This is of central anatomical importance because the position of its origin from the ileocaecal region of mesentery partly determines the anatomical location of the appendix (that is, retrocaecal or pelvic) |
| Dorsal mesentery | The region of mesentery contiguous with the abdominal wall, including the dorsal mesogastrial, omental, mesoduodenal, small intestinal mesenteric, mesocolic, mesosigmoidal and mesorectal regions | |
| Ventral mesentery | The region of mesentery contiguous anterior and posterior with the abdominal wall and dorsal mesogastrium, respectively, and consisting of ventral mesogastric and falciform regions | |
| Mesenteric root region | The area where the upper (mesogastric and mesoduodenal) mesentery narrows and then fans out as the small intestinal mesentery ( Fig. 57.3 ; see Fig. 57.1D ). | |
| Retroperitoneum | The abdominal wall posterior to Toldt's fascia (see Fig. 57.1C ) | |
| Ventral mesogastrium (lesser omentum) | Mesentery bridging the liver and the stomach or duodenum (see Fig. 57.1E ) | |
| Dorsal mesogastrium | Mesentery bridging the stomach and posterior abdominal wall (see Fig. 57.1D,E ) | |
| Greater omentum | The fibroadipose structure extending inferiorly and laterally from the greater curvature of the stomach | |
| Small intestinal mesentery | Mesentery associated with the small intestine (see Fig. 57.1F ) | |
| Surgical terminology | ||
| Plane | A conceptual interface between two continuous and contiguous surfaces | This is best illustrated by an example. The mesofascial plane is formed by the mesentery and underlying fascia; both are continuous and contiguous (that is, in contact). The plane is the conceptual zone between both. This is centrally important in abdominal surgery because separation of planar components (that is, mesentery and fascia) is a cornerstone of all intestinal surgery |
| Mesenteric detachment | Detachment of a region of mesentery from underlying contiguous fascia | Detachment of an intact mesenteric package is a core technical goal in intestinal surgery. Detachment is complete when the mesentery remains connected only by either adjacent mesentery or vascular points of connectivity at an adipovascular pedicle |
| Mesofascial separation | Separation of the mesentery from underlying fascia | Mesofascial separation over a broad region results in mesenteric detachment |
| Colofascial separation | Separation of the colon from underlying fascia | Colofascial separation over a broad region results in colic detachment |
| Mesenteric disconnection | Division of all anatomical connections remaining after complete mesenteric detachment | Vascular, mesenteric (between adjacent regions) and intestinal connections are all that remain to connect the detached mesentery. Once these are divided, the mesentery (and, by definition, the intestine) is fully disconnected and can be removed |
| Peritonotomy | Sharp incision of the peritoneum | Peritonotomy, followed by traction and counter-traction, is used to expose mesentery, fascia and the mesofascial plane |
| Adipovascular pedicle | Fat heaping around major vessels that helps differentiate these from non-vascular mesentery (see Fig. 57.6 ) | Adipovascular pedicles include the ileocolic, middle colic, inferior mesenteric and left colic pedicles. Where multiple vessels are in close proximity, pedicles are not readily identifiable: for example, in the dorsal mesogastrium following division of the coeliac trunk, and in the mesosigmoid, where multiple sigmoidal branches of the superior rectal artery lie in relatively close proximity. The inferior margin of the ventral mesogastrium (previously the hepatoduodenal ligament) is a mesenteric pedicle containing the hepatic artery, portal vein and common bile duct, and can be readily differentiated from the non-pedicular region of the ventral mesogastrium (previously the gastrohepatic ligament) |
| Embryological terminology | ||
| Non-rotation (also called malrotation) | Incomplete embryological development of the mesentery, resulting in the right colon and mesocolon taking up a central abdominal position | Development of the mesentery ceases at a certain point, which means the right mesocolic region of the mesentery does not take up a position to the right of the small intestinal mesentery, and instead remains positioned to the left of the developing small intestine and mesentery. The condition is associated with non-attachment of the mesentery |
| Attachment | Flattening and anchorage of mesentery to the posterior abdominal wall across Toldt's fascia | The right and left mesocolon, medial region of the mesosigmoid and mesorectum attach or flatten against the posterior abdominal wall. Importantly, this meaning differs from previous interpretations of ‘attachment’, according to which the mesentery inserted directly into the posterior abdominal wall along a linear trajectory |
| Non-attachment | Incomplete or absent mesenteric attachment | This is of considerable surgical and pathobiological importance because it is associated with volvulus in the adult |
| Congenital adhesions | Adhesions between two peritonealized surfaces in prolonged and uninterrupted contact | Examples of surgical relevance occur at the lateral aspect of the mesosigmoid between the surface of the mesosigmoid and the peritoneum of the left iliac fossa. A further important example is the adhesions between the undersurface of the greater omentum and the upper surface of the transverse mesocolon |
History
Until recently, the widely accepted model of the mesentery described multiple ‘mesenteries’ ( 
). This was supported by the 1888 findings of Sir Frederick Treves, which were incorporated in all mainstream anatomical, radiological and surgical literature. Treves's descriptions echoed those of Henry Gray, who, in 1858, first used the term ‘mesenteries’ in his reference text on anatomy. This was a departure from the Renaissance interpretations of Eustachius, Vesalius and Da Vinci. Each depicted (but did not explicitly describe) mesenteric continuity using the term ‘mesenterium’. ‘Mesenterium’ was substituted by the terms ‘mesocolon’ and ‘small bowel mesentery’ during the nineteenth century. The recent identification of a right and a left mesocolon led to the recognition of mesenteric continuity between the small intestinal mesentery and right mesocolon ( Fig. 57.1A ). Continuity from the duodenojejunal flexure to the mesorectal level was next confirmed (see Fig. 57.1A ). Emerging data indicate that the mesentery is continuous from mesogastrium to mesorectum and is narrowed centrally at the mesenteric root region (see Fig. 57.1D ). One of the consequences of this continuity is that there are no distinctive landmarks to indicate the anatomical limits of adjacent regions. Notwithstanding, a nomenclature has developed with reference to each different region (see Table 57.1 ).
Flexures
A flexure occurs between each region of the duodenum; at the ileocaecal junction; at hepatocolic and splenic levels; at the junction between the descending and sigmoid colon; and between the sigmoid colon and rectum. With the exception of the flexure between the second and third parts of the duodenum, a flexure occurs where the intestinal tract changes from attached (to the posterior abdominal wall) to mobile (or vice versa ). Given the continuity and contiguity of the intestine, mesentery, peritoneum and fascia, each flexure can be explained in terms of these components.
The flexures most frequently encountered during abdominal surgery are the hepatic and splenic flexures. Flexures share a common underlying anatomical framework: the hepatic flexure will be described here as an exemplar. The mesenteric component of the hepatic flexure is a confluence between the right and transverse regions of the mesocolon and is best described in terms of radial and longitudinal axes. The radial axis of the hepatic and splenic flexures extends radially from the middle colic vascular pedicle to the intestinal margin of the mesentery. During this course, the mesentery changes from attached (to the posterior abdominal wall) to non-attached and mobile. The longitudinal axis extends longitudinally from one mesenteric region to the next in sequence. At the hepatic flexure, the right mesocolic region is fully attached, whereas at the transverse mesocolic region, the mesentery is attached centrally but mobile at the intestinal margin; the reverse occurs at the splenic flexure.
Embryology
This field is broad and will be briefly summarized. Dorsal and ventral mesenteric regions form early in embryological development and provide a mesenteric framework in which numerous organs develop. Development is easily conceptualized when divided into that above and below the mesenteric root region (see earlier). Above the root region, the stomach and liver develop in mesogastric mesentery. This persists into adulthood as the falciform ‘ligament’, the ventral and dorsal mesogastrium. The pancreas develops at the level of the mesoduodenal mesentery. Below the root region, the small intestinal region of mesentery elongates and coils extensively at its intestinal margin. Following return of the intestine and mesentery post herniation, both adopt a conformation in which the right colon and associated mesentery are on the right, and small intestine and associated mesentery are in the middle. The left colon and mesentery are positioned to the left (see Fig. 57.1F ). Importantly, mesenteric continuity is retained into adulthood (see Fig. 57.1A ).
‘Rotation’ is the term used to denote the process whereby the midgut region of the intestinomesenteric complex changes position from the middle region of the developing peritoneal cavity to the right side of the cavity. As a result, the small intestine and mesentery (initially located on the right) are displaced to a central position between the right colon and mesentery (on the right) and the left colon and mesentery (on the left). ‘Attachment’ is the process whereby regions of mesentery become flattened and anchored against the posterior abdominal wall. A fascial layer develops between both to anchor them together in position ( Figs 57.4 , 57.5 ; see Fig. 57.1C ). If rotation does not occur (that is, ‘non-rotation’), then the small intestine and mesentery are not displaced centrally. In addition, the right mesocolon does not become attached to the posterior abdominal wall on the right side, and its attachment (or anchorage) fails. The result is a mesentery (and, by definition, intestine) that may twist around the narrow root region, with devastating consequences.
Other defects of embryological development include non-attachment, situs inversus and atresia. In non-attachment ( Ch. 66 ), the mesentery has the correct conformation, but does not adequately attach and is prone to twisting. This is called a volvulus. In atresia ( Ch. 66 ), a region of mesentery and the corresponding region of intestine do not form normally. A gap occurs in the mesentery (usually in the region of the intersection with the intestine), around which the normal mesentery continues to develop. In situs inversus, organs ordinarily positioned on the left are now on the right and vice versa. The conformation of the mesentery, peritoneum, intestine and related organs is the same as seen in normality, only in reverse.
Congenital adhesions
Focal ‘congenital’ adhesions occur wherever two mesothelial surfaces come into prolonged and relatively uninterrupted contact. They can occur anywhere but tend to be mainly focused in certain regions, including the lateral aspect of the mesosigmoid, where this is in close contact with the peritoneum of the left iliac fossa, and between the undersurface of the greater omentum and the upper surface of the transverse mesocolon. It is not uncommon for them to be mistaken for the peritoneal reflection.
Mesentery
The following is a description of the anatomical model of the mesentery, on which surgery of the upper and lower gastrointestinal tract is based ( ). The mesentery proximal to the mesenteric root region is described first, followed by the mesentery distal to the mesenteric root region.
Anatomy proximal to the mesenteric root region
Dorsal mesogastrium and mesoduodenum
The dorsal mesogastrium is a region of mesentery in the posterior wall of the lesser sac (see Fig. 57.1A,D ). Toldt's fascia lies posterior to it, separating it from the retroperitoneum (see Fig. 57.1C ). The mesogastrium may be detached from the fascia via mesofascial separation (see earlier). This activity aids in identifying and surgically controlling vessels that enter the mesogastrium from the coeliac trunk (see Fig. 57.1D ). At the oesophago-gastric junction, the mesogastrium narrows to an apex, from which it continues into the thorax as the meso-oesophagus. At the lesser curvature of the stomach, the mesogastrium curves sharply forward towards the liver as the ventral mesogastrium (see Fig. 57.1E ). Inferiorly, the dorsal mesogastrium continues as the mesoduodenum, which narrows anteroposteriorly; in front of it lies the pancreas (see Fig. 57.1E ). The dorsal mesogastrium continues laterally as the splenic hilum to the spleen. The mesoduodenum narrows in all planes as it approaches the mesenteric root region (see Fig. 57.1E ). Regions of the developing mesoduodenum cradle the origin of the superior mesenteric artery and the termination of the superior mesenteric vein in the mesentery of the root region. The latter is of considerable anatomical and surgical importance. The body of the pancreas is above and anterior to the root region, while the head, and in particular the uncinate process, are posterior to and below it. From here, the mesentery fans out extensively to span the intestine distal to the duodenojejunal flexure (see Figs 57.1D,F, 57.3 ).
The spleen is located in the left upper quadrant under the left hemidiaphragm (see Fig. 57.1E ). The lienorenal peritoneal reflection is at the lateral margin of the spleen and curves superomedially as the lienophrenic reflection. Together, these regions of peritoneal reflection form the upper lateral boundary of the lesser sac and the lateral limit of the dorsal mesogastrium (see Fig. 57.1B ). On the right, the dorsal mesogastrium is limited by the liver, where it is apposed to the abdominal wall at the bare area (see Fig. 57.1B,C ).
Ventral mesogastrium
The relationship between the ventral and dorsal mesogastria (as well as the ventral and dorsal mesoduodena) is of considerable anatomical importance (see Fig. 57.1E ). Continuity provides the mesenteric frame in which branches of the coeliac trunk reach many different organs. It is also the anatomical frame in which elements of the biliary tree and portal venous system pass from one organ to another (see Fig. 57.1D ).
In the adult, the portal vein, bile duct and hepatic artery are located in the inferior margin of the ventral mesogastrium. Previously, this region was termed the ‘hepatoduodenal ligament’ and the remainder of the ventral mesogastrium was called the ‘gastrohepatic ligament’. As neither term has a distinct anatomical correlate and their usage is confusing, they are not used here (see Table 57.1 for further explanation). The inferior margin of the ventral mesogastrium is thickened compared with the rest of the mesogastrium, giving rise to a pedicle (the ‘portal pedicle’) ( Fig. 57.6 
; see Fig. 57.1D,E ).
Greater omentum
The greater omentum is suspended from the greater curvature of the stomach; the gastroepiploic arterial arcade is at their intersection. The greater omentum is apposed to the upper surface of the transverse mesocolon in a highly variable manner that is mediated by diffuse adhesions between both structures. A similar mechanism of attachment occurs between the greater omentum and the peritoneal reflection at the hepatic and splenic flexures. Attachment to the splenic peritoneal reflection is usually extensive, which has implications for surgical mobilization of the splenic flexure. A peritoneal reflection occurs between the greater omentum and the upper border of the transverse colon; it is well developed in the midline region but narrows laterally to an apex at either pole of the transverse colon.
Falciform ‘ligament’
The falciform ‘ligament’ is the most anterior remnant of the ventral mesogastrium. It is a midline structure located between the anterior surface of the liver and the inner surface of the anterior abdominal wall. Its inferior border is thickened and called the ligamentum teres. Superiorly, it narrows towards an apex, from which the triangular and coronary peritoneal reflections of the liver extend laterally.
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here