The endoabdominal fascia lines the abdominal cavity. It is comprised of:
- Transversalis fascia: outer layer. Lies between the inner surface of the transverse abdominis muscle and the extraperitoneal tissue.
- Extraperitoneal tissue: this is a layer of connective tissue between the transversalis fascia and parietal peritoneum.
- Parietal peritoneum (or fascia): this layer is a thin serous membrane acting as a balloon which lines the abdomen and into which the organs are pressed into from the outside.
- Visceral peritoneum (or layer): inner layer. This layer lines the organs and is known as the visceral peritoneum in the abdomen, pleura around the lungs (Gallaudet, 1931) and pericardium around the heart.
Li (2012) defined the transversalis fascia as lining the inner surface of the transversus abdominis. It can be divided into two layers, superficial and deep with a dividing intermediate layer:
- Superficial layer of the transversalis fascia: closely covers the internal surface of the transversus abdominis and its aponeurosis.
- Intermediate layer: is an amorphous fibroareolar space filled with fat and loose fibrous tissue. It lies between the superficial and deep layers of the transversalis fascia.
- Deep layer of the transversalis fascia: lies underneath the intermediate layer. It is seperated from the peritoneum by a loose amorphous fibroareolar space.
Superiorly the superficial and deep layers fuse to form the fascia covering the inferior surface of the diaphragm. Forming the subdiaphragmatic fascia the transversalis fascia travels through the medial and lateral arcuate ligaments and aortic hiatus to become the endothoracic fascia. Apaydin et al (2008) found the transversalis fascia also blended with the endothoracic fascia at the oesophageal hiatus to form the phrenico-esophageal ligament. This ligament attaches the oesophagus to the right diaphragmatic crura at the oesophageal hiatus.
Anteriorly the superficial layer covers the inner surface of the transversus abdominis and the posterior rectus sheath (or the rectus abdominis muscle). The deep layer lines the outer surface of the peritoneum.
Posteriorly the superficial and deep layers join together and form a continuous sheet anterior to the lumbar fascia.
Running from an anterior to posterior direction the transversalis fascia courses laterally over the quadratus lumborum and then medially over the psoas major. At these points the transversalis fascia gets renamed the quadratus lumborum and psoas fascia respectively.
As the transversalis fascia is the fascia of the quadratus lumborum and psoas it extends superiorly to form the subdiaphragmatic fascia. At this point it forms the arcuate ligaments and, with the endothoracic fascia, the phrenico-esophageal ligament (Apaydin eat al (2008).
The lateral arucate ligament (rib 12 to L1 TP) is a thckening of the quadratus lumborum fascia. The medial arcuate ligament (L1 body to L1 TP) is a thickening of the psoas fascia.
Laterally Li et al (2012) found the superficial and deep layers of the transversalis fascia to join at the:
- Outer edge of the quadratus lumborum (at the level of the renal hilum)
- Outer edge of the psoas major (at the level of L3).
- Anterior axillary line.
Also at the outer edge of the quadratus lumborum the transversalis fascia blends with the lateral conal fascia* (Li et al 2012).
*: Lateral conal fascia is formed by the lateral fusion of the anterior and posterior renal fascia. It then travels laterally inrelation to the posterolateral aspect of the colon and fuses with the lateral parietal peritoneum.
Inferiorly the transversalis fascia is continuous with the endopelvic fascia.
Inferiorly Meyer (1927) found the transversalis fascia, along with the pelvic fascia with which it is continuous, tightly adherent to the pelvic brim. Hayes (1950) found anteriorly at the pelvic brim the transversalis fascia blends with the periosteum of the dorsal surface of the superior pubic ramus and pubic crest.
Spaces between the superficial and deep layers of transversalis fascia
The spaces between the superficial and deep layers of the transversalis fascia are:
- Extraperitoneal space: the space between the superficial and deep layers of the transversalis fascia.
- Retroperitoneal space: space behind the peritoneum in the abdominal cavity.
- Retzius space: the space between the symphysis pubis and bladder.
- Retroinguinal (Bogros) space: is bound by the transversalis fascia anteriorly, the peritoneum posteriorly and the fascia iliacus laterally.
- The inferior epigastric vessels: these vessels penetrate the superior layer of the transversalis fascia as they originate from the external iliac vessels. They run in the matrix between the two layers and then penetrate the superficial layer of the transversalis fascia at the level of the linea arcuata and run into the rectus sheath.
Parietal and visceral peritoneum
- Parietal peritoneum (or fascia): this layer is a thin serous membrane acting as a balloon which lines the abdomen and into which the organs are pressed into from the outside.
- Visceral peritoneum (or layer): this layer lines the organs. It is known as the visceral peritoneum in the abdomen, pleura in the thorax (Gallaudet, 1931) and pericardium around the heart.
- Between these parietal and visceral layers is a closed sac with a potential space. This space is called the peritoneal cavity, the pleural space and pericardial cavity.
The parietal and visceral peritoneum are continuous at:
- Sides and anterior surface of the ascending and descending colon.
- Falciform ligament.
- Lateral margin and part of the anterior surface of the left kidney.
- Toldt's fascia: visceral peritoneum of the mesocolon fuses with the parietal peritoneum of the retroperitoneum. Separates the mesentery from the retroperitoneum.
- Retroperitoneal segments of the bowel: most of the duodenum, ascending colon, descending colon and rectum.
- Intraperitoneal bowel loops suspended by the mesentery: loop one (abdominal oesphagus, stomach and D1). Loop two (duodenojejunal junction, jejuneum, ileum and usually the caecum). Loop three (transverse colon). Loop four (sigmoid colon and occassionally the descending colon).
In the region of the aorta and inferior vena cava the parietal peritoneum is continuous with the mesentery of the small intestine.
Where the visceral peritoneum encloses or suspends organs within the peritoneal cavity, the peritoneum and its related connective tissue forms peritoneal ligaments, omenta and mesenteries.
The peritoneal ligaments are formed by fused double layers of peritoneum:
Gastrohepatic ligament: lesser omentum. Stomach: lesser curvature --> liver: fissure for ligamentum venosum.
Hepatoduodenal ligament: free margin of the lesser omentum. Liver: porta hepatis --> D1 and D2: flexure between D1 and D2.
Gastrosplenic ligament: left lateral extension of the greater omentum and lateral boundary of the lesser sac. Stomach: greater curvature --> spleen.
Splenorenal (lienorenal) ligament: left kidney --> spleen. Surrounds the pancreatic tail and extends to the left anterior pararenal space.
Gastrocolic ligament: greater omentum. Stomach: greater curvature --> transverse colon.
Transverse mesocolon & sigmoid mesocolon: the mesocolon attaches the colon to the posterior abdominal and pelvic wall. Refer 'mesenteries'.
Falciform ligament: separates the liver into the right and left lobes. Peritoneum behind the right rectus abdominis and diaphragm --> Liver: courses cranially along the anterior surface of the liver, blending into the hepatic peritoneal covering and then carries on posterosuperiorly to become the anterior portion of the left and right coronary ligaments. Contains the ligament teres (round ligament).
Ligamentum teres (round ligament): a remnant of the obliterated umbilical vein (ductus venosus). Anterior portion is an extension of the falciform ligament. Liver: umbilical fissure --> umbilicus.
Coronary and triangular ligaments: liver --> diaphragm: inferior surface. Bare area* of the liver is delineated by the coronary ligament centrally (anteriorly and posteriorly) and the right and left triangular ligaments laterally.
* Bare area of liver: the cranial aspect of the liver is a convex area along the diaphragmatic surface. It is devoid of any ligamentous attachments or peritoneum. This bare area of the liver is attached to the diaphragm by flimsy fibroareolar tissue.
Phrenicocolic ligament: left lateral extension of the root of the transverse mesocolon. Diaphragm: opposite left r10 & r11 --> Transverse-descending colon: left (splenic) colic flexure. Passes below the spleen acting as a suspensory ligament of the spleen.
Duodenocolic ligament: right colon --> duodenum.
Liver: potra hepatis and fossa for the ductus venosus --> stomach: lesser curvature (hepatogastric ligament) and duodenum: D1 (heaptoduodenal ligament).
From the liver attachment at the ductus venosus this connective tissue ascends to the diaphragm where it attaches to the oesophagus.
The lesser omentum is often defined to encompass a variety of structures:
- Hepatogastric ligament.
- Hepatoduodenal ligament.
- Hepatophrenic ligament.
- Hepatoesophageal ligament.
- Hepatocolic ligament.
Greater curvature of the stomach (right border: D1) --> descend in front of the small intestines --> ascend to, and encloses, the transverse colon.
The left side of the greater omentum is continuous with the gastrosplenic ligament.
The greater omentum is often defined to encompass a variety of structures:
- Gastrocolic ligament: occasionally considered synonymous with the greater omentum.
- Phrenicosplenic ligament.
- Gastrophrenic ligament.
- Gastrosplenic (gastrolienal) ligament.
- Splenorenal (lienorenal) ligament: occasionally considered part of the greater omentum.
The phrenicosplenic, gastrophrenic, gastrosplenic and splenorenal (lienorenal) ligaments are all part of the same mesenteric sheet making the divisions between them fairly arbituary.
The mesenteries are a double fold of peritoneum that attaches the intestines to the posterior abdominal wall. The mesenteries are classified as the mesentery of the small intestine (the mesentery proper) and the mesentery of the large intestine (the mescolon).
Mesentery of the small intestine (mesentery) proper
The mesentery of the small intestine is a large and broad fan-shaped mesentery. It extends from the D/J junction (just to the left of L2) to the I/C junction (anterior to the right SIJ) and then attaches to the posterior abdominal wall.
Mesentery of the large intestine (mesocolon)
- Mesoappendix: appendix --> back of the lower end of the mesentery close to the I/C junction.
- Transverse mesocolon: transverse colon --> posterior abdominal wall. Connects to the pancreas, duodenum and greater omentum.
- Sigmoid mesocolon: sigmoid colon --> pelvic wall. Forms an inverted 'V' attachment. The apex of the 'V' is at the level of the division of the left common iliac artery (anterior to the left sacroiliac joint). The base of the right limb descends to the median plane at the level of S3. The left limb descends on the medial side of the left psoas major.
Sometimes the ascending and descending colon is attached to the posterior abdominal wall by the ascending and descending mesocolon. However, it is more common for the peritoneum to only cover the front and sides of the ascending and descending colon.
The mesorectum is the fat surrounding the rectum. It blends superiorly with the sigmoid mesentery and extends down to the levator ani. It is enclosed by the mesorectal fascia. Chang et al (2019) found anatomically the mesocolon extended as one continuous structure. They identified the mesocolon as extending from the descending colon through the sigmoid colon and then running further into the pelvis to become the mesorectum.
Coffey et al (2015) took this continuity further. They dismissed the idea of seperate mesenteries for the small and large intestine and identified the continuity of one single mesentery from the D/J junction to the distal mesorectum. Interestingly the attachments these authors describe parallel the work of Leonardo da Vinci.
These authors described the root of the mesentery starting from where the superior mesenteric artery originates from the pancreatic bed (retroperitoneal space the pancreas and D1 shares). From this location, the mesentery fans out to span the entire gastrointestinal tract from the D/J junction to a termination at the distal mesorectum.
Where the mesentery is apposed to the retroperitoneum, its surface area is limited. However, as it attaches on to the gastrointestinal tract, it elongates considerably. They describe approximately 6 feet of elongated mesentery is compactly plicated into the abdominal cavity and tightly packaged in a spiral formation.
As well as Coffey et al (2015) finding the root of the mesentery to originate at the superior mesenteric artery Martin (1942) also found the anterior renal fascia to cover the mass of connective tissue surrounding the origins superior mesenteric artery.
The retroperitoneal connective tissue is divided into three layers:
- Outer layer: transversalis fascia.
- Intermediate layer: these tissues are locally condensed or specialized forming the fascia for the kidneys (renal fascia), adrenals, kidneys, ureters, and the vessels and nerves.
- Inner layer: peritoneum.
As this is retroperitoneal tissue obviously all the layers will be behind (superficial) to the peritoneum.
The renal fascia is divided into the:
- Anterior renal fascia (Gerota fascia or fascia of Tobdt).
- Posterior renal fascia (Zuckcnkandl fascia).
The anterior renal fascia as a single lamina is thinner than the posterior renal fascia which is a double lamina (Bechtold et al 1996). Stecco et al (2017) described the renal fascia as a zone of dense endoabdominal fascia.
These two fascia encompass the kidney to form an inverted cone of tissue that lies lateral to the lumbar spine and extends into the pelvis.
This cone is formed by the kidneys being embryologically formed in the pelvis. As they migrate superiorly to their normal adult position the fascia surrounding them migrates with them forming a long tapered cone.
The space between the anterior and posterior renal fascia is called the perirenal space. Septa traverse this space connecting the anterior and posterior renal fascia as well as the renal capsule with the renal fascia.
The perirneal space contains: containing the kidneys, adrenals and proximal ureters.
The boundaries of the renal fascia are:
- Superiorly: fuses with the posterolateral aspect of the hemidiaphragm. The right anterior and posterior renal fascia blends with the right inferior coronary ligament.
- Posteriorly: quadratus lumborum (transversalis) fascia. Martin (1942) removed a block of tissue from r11 and r12 to the iliac crest attaching anteriorly to the quadratus lumborum muscle. When this tissue was removed followed by the quadratus lumborum muscle the posterior layer of the renal fascia was exposed.
- Medially: at the renal hilar level, and caudally from this level, the renal fascia fuses with the lateral margin of the quadratus lumborum (transversalis) fascia.
Martin (1942) found medially the anterior renal fascia splits into a superficial and deep laminae. Superficial layer: up to the origin of the superior mesenteric artery this layer crosses the midline to form a mass of connective tissue in front of the aorta and inferior vena cava. Here it blends with the anterior renal fascia from the opposite kidney. Above the level of the superior mesenteric artery the anterior renal fascia covers the mass of connective tissue surrounding the origins of the coeliac axis and superior mesenteric artery (in which lie the coeliac and superior mesenteric autonomic plexuses). Deep layer: passes backwards around the medial border of the kidney becoming firmly adherent to the front of the renal hilum and then continues to join the posterior renal fascia.
As well as Martin (1942) finding the anterior renal fascia to cover the mass of connective tissue surrounding the origins of the coeliac axis and superior mesenteric artery Coffey et al (2015) found the root of the mesentery to start also at the superior mesenteric artery.
The posterior renal fascia splits at the medial boarder of the kidney. One layer turns into the hilum of the kidney and becomes firmly attached to the posterior aspect of the the ureter. The second layer blends with the psoas major (transversalis) fascia especially at the medial and lateral edges of the psoas.
- Laterally: the posterior renal fascia blends with the anterior renal fascia forming the lateralconal fascia. Martin (1942) found the renal fascia also fuses laterally with the transversalis fascia.
- Inferiorly: the posterior and anterior renal fascia gradually converges, but does not fuse, towards a point about 8 cm inferior to the lower pole of the kidney (Bechtold et al 1996). The perirenal space blends loosely with the iliac fascia and periureteric connective tissue.
Anterior and posterior pararenal spaces
As the kidneys are retroperitoneal they are behind the outer (parietal) layer of the peritoneum. But in front of the superficial transversalis fascia.
Between the posterior renal fascia (anteriorly) and transversalis fascia (posteriorly) is the posterior pararenal space. This space is limited medially by the psoas major, superiorly by the fusion of the retrorenal, psoas and quadratus lumborum fascia and inferiorly it opens into the pelvis and communicates with the anterior pararenal space.
Between the anterior renal fascia (posteriorly) and the parietal peritoneum (anteriorly) is the anterior pararenal space.
The anterior pararenal boundaries are:
- Superiorly: diaphragm.
- Anteriorly: posterior parietal peritoneum.
- Laterally: lateralconal fascia.
- Posteriorly: anterior renal fascia.
- Medially: continuous with contralateral anterior pararenal space.
- Inferiorly: iliac fossa and posterior pararenal space.
Contains: pancreas, retroperitoneal segments of the duodenum, ascending and descending colon and the mesenteric root.
With the relation of the anterior pararenal space and descending colon Chang et al (2019) found the anterior renal fascia along the descending colon segment extended as the urogenital fascia in the sigmoid colon segment and visceral fascia in the pelvis.
Superior mesnteric artery
The superior mesenteric artery is an important landmark for the anterior renal fascia, mesentery and the suspensory ligament of the duodenum (ligament of Treitz).
Martin (1942) found below the superior mesenteric artery the anterior renal fascia crosses the midline to join the contralateral anterior renal fascia and superior to the artery it covers the mass of connective tissue surrounding the origins of the coeliac axis (artery) and superior mesentery artery (in which lies the coeliac and superior mesenteric autonomic plexus).
Coffey et al (2015) found the root of the mesentery for the small and large intestine to start from where the superior mesenteric artery originates from the pancreatic bed (retroperitoneal space the pancreas and D1 shares).
Suspensory ligament of the duodenum (ligament of Trietz): double fold of peritoneum. It comprises two parts: part one: right crus of diaphragm --> connective tissue around coeliac and superior mesenteric artery. Part two: muscular part which suspends D/J junction. Connective tissue around coeliac artery --> duodenum: between pancreas and left renal vein.
The surface anatomy of this area is discussed to aid in the use of any osteopathic techniques.
The superior mesenteric artery originates from the anterior surface of the abdominal aorta slightly to the right of the D/J junction. The suspensory ligament of the duodenum (ligament of Trietz) as well as suspending the D/J junction from the retroperitoneum surrounds and protects the superior mesenteric artery and coeliac trunk.
The origin of the superior mesenteric artery from the abdominal aorta is at the level of L1 which corresponds to the transpyloric plane (half way between the xiphoid and umbilicus) close to the left midclavicular-umbilical line.
The artery then descends to the right iliac fossa supplying along its course the pancreas and intestine (lower part of the duodenum --> appendix, ascending and transverse colon).
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