Endoabdominal Fascia
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.
Transversalis fascia
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 separated from the peritoneum by a loose amorphous fibroareolar space.
Superiorly
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
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
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 thickening of the quadratus lumborum fascia. The medial arcuate ligament (L1 body to L1 TP) is a thickening of the psoas fascia.
Laterally
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 lateroconal fascia* (Li et al 2012).
*: Lateroconal fascia is the peritoneal thickening extending from the lateral fusion of the anterior and posterior renal fascia.
Inferiorly
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.
Peritoneum
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.
Peritoneal ligaments
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 --> large intestine: left (splenic) colic flexure. Passes below the spleen acting as a suspensory ligament of the spleen.
Duodenocolic ligament: right colon --> duodenum.
Omentum
Lesser omentum
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 omentum
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.
Mesenteries
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
Coffey et al (2015) found the mesenteric origin i.e. its root is where the superior mesenteric artery distributes from the pancreatic bed (retroperitoneal space the pancreas and D1 shares).
Coffey and O’Leary (2017) found the mesentery to be suspended by the superior mesenteric artery alone, with a resultant tendency to twist around it. This suspensions holds the mesentery up preventing it from collapsing down into the pelvis.
From this location, the mesentery fans out to span the entire gastrointestinal tract from the D/J junction to the termination at the distal mesorectum. Interestingly the attachments these authors describe parallel the work of Leonardo da Vinci.
The mesentery of the small and large intestine is thus likened to a Chinese fan.
The handle of the fan is the mesenteric root twisted around the superior mesenteric artery.
The leaves of the fan, the small intestine mesentery, flatten against the posterior abdominal wall, attached to it by a peritoneal reflection, on a line running from just to the left of L2 (D/J junction) to the right anterior sacroiliac region (I/C junction) and then onto the small intestine.
These leaves of the small intestine mesenetery continue laterally forming (i & ii) the ascending and descending mesocolon (terminating at the mesorectum) attaching the ascending and descending colon to the posterior abdominal wall and (iii) the transverse mesocolon attaching the transverse colon to the superior mesenteric artery. Standring (2015) also found the transverse mesocolon can be attached to the small intestine mesentery at the D/J flexure by a peritoneal band.
Okino et al (2001) found the root of the mesentery contiguous with:
Superiorly: hepatoduodenal ligament around the superior mesenteric vein and portal vein*.
Anteriorly: transverse mesocolon around the gastrocolic trunk and uncinate process of the pancreas. The gastrocolic trunk represents the convergence of the transverse mesocolon, greater omentum, and mesenteric root (Aldouri 2017).
Posterolaterally: ascending and descending mesocolons (anterior pararenal space).
Superior mesenteric artery and vein and the gastrocolic trunk pass through the root of the mesentery (Aldouri 2017)
*: the portal vein is formed at the confluence of the splenic vein and superior mesenteric vein. It passes into the liver via the hepatoduodenal ligament at the liver hilum.
Mesentery of the large intestine (mesocolon)
The mesocolon is the part of the mesentery that attaches the colon to the posterior abdominal wall. Traditionally the mesocolon has been described as a separate structure to the small intestine mesentery.
Its traditonal classifications are:
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.
The ascending and descending colon was described as sometimes being attached to the posterior abdominal wall by the ascending and descending mesocolon. However, it was more commonly described as the peritoneum only covering the front and sides of the ascending and descending colon.
In contradiction to this tradtional view Coffey et al (2015) found:
The mesocolon is a continuous structure with the small intestine mesentery.
The ascending mesocolon is always present and attaches (i.e. flattens against) the posterior abdominal wall.
The descending mesocolon is always present and attaches (i.e. flattens against) the posterior abdominal wall.
The descending mesocolon is continuous at its superior end with the transverse mesocolon and its inferior end with the mesosigmoid and mesorectum (and Chang et al 2019)*.
These authors describe the transverse mesocolon as best thought of as being the structure generated where the mesenteric components of the hepatic and splenic flexure converge with the origin of the middle colic artery (i.e. at the superior mesenteric artery).
As opposed to being attached to the posterior abdominal wall, like the ascending and descending colon, it is attached to the origin of the middle colic artery (i.e. at the superior mesenteric artery).
The attachment of the transverse mesocolon to the superior mesenteric artery makes it more mobile than the ascending and descending mesocolons that are attached more rigidly to the posterior abdominal wall.
Between the ascending and descending mesocolon and the posterior abdominal wall (retroperitoneum) is Toldt's fascia. Therefore the mesocolon is attached to Toldt's fascia forming the colofascial plane.
*: 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.
Vikram et al (2009) found the transverse mesocolon continuous with the splenorenal ligament (left kidney --> spleen) and the phrenicocolic ligament (diaphragm opposite r10 & 11 --> large intestine: left (splenic) colic flexure).
Vikram et al (2009) also found the root of the transverse mesocolon to extend across D2 and the pancreas.
As well as Coffey et al (2015) finding the root of the mesentery and transverse mesocolon 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. This artery also gives attachment to the suspensory ligament of the duodenum (ligament of Treitz).
Therefore the transverse mesocolon is continuous with:
Splenorenal ligament: left kidney and spleen.
Phrenicocolic ligament: diaphragm.
Duodenum: D2 (& D1 via the greater omentum, refer below).
Pancreas.
Anterior renal fascia.
Suspensory ligament of the duodenum (ligament of treitz): right crus of diaphragm and D/J flexure.
Root of the small intestine mesentery: as well as a similar insertion on the superior mesenteric artery the transverse mesocolon can be attached to the small intestine mesentery at the D/J flexure by a peritoneal band (Standring 2015).
Via the transverse colon: greater omentum and gastrocolic ligament attaches to the stomach and D1.
Renal fascia
The retroperitoneal connective tissue is divided into four layers:
Outer layer: transversalis fascia.
The next layer in are the tissues that are locally condensed or specialised forming the fascia for the kidneys (renal fascia), adrenals, kidneys, ureters, and the vessels and nerves.
Toldt's fascia: lies between the retroperitoneal structures and peritoneum. This fascia tightly fuses with the anterior renal fascia whereby some authors class the anterior renal fascia and toldt's fascia as being the same entity.
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 perirenal 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. The deep layer of the renal fascia extends continues with the transversalis fascia at the level of the vertebral body (Li et al 2021).
Anteriorly: anterior renal fascia and where it fuses with Toldt's fascia (refer 'Toldt's fascia').
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 from L3-L5 (Coffin et al 2014). 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 and transverse mesocolon to start also at the superior mesenteric artery. This artery also gives attachment to the suspensory ligament of the duodenum (ligament of Treitz).
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: at the posterior axillary line the posterior renal fascia blends with the anterior renal fascia . The lateroconal fascia is the peritoneal thickening that extends from the fusion of the anterior and posterior renal fascia. Martin (1942) found the renal fascia also fuses laterally with the transversalis fascia at the lateral edge of the quadratus lumborum.
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 (lower urogenital fascia).
Lower urogenital fascia
As an extension of the renal fascia the lower urogenital fascia (these two fascia are typically described together as the urogeniotal fascia) has the same superficial and deep layer (Li et al 2021).
At the pelvic brim the ureters, vas deferens, genital vessels, superior hypogastric plexus, seminal vesicles, prostate, and urinary bladder are ensheathed by both layers of the urogenital fascia (Li et al 2021).
In the inguinal region, the deep and superficial layers ensheathed the vas deferens and spermatic vessels and move through the deep inguinal ring. From the deep inguinal ring to the midline, the superficial layer extends to the posterior wall of the urinary bladder, whereas the deep layer extends to the anterior wall of the urinary bladder. The deep and superficial layers wraps around the urinary bladder and extends along the medial umbilical ligament to the umbilicus (Li et al 2021).
At the sacral promontory the deep and superficial layers extends along the sacrum, forming the presacral fascia. The superficial layer (superficial layer of the presacral fascia) forms the rectosacral fascia at S4; the deep layer (deep layer of the presacral fascia) extends to the pelvic diaphragm terminating at the levator ani.
Due to the attachment of the levator ani to the pubic symphysis Ramin et al (2015) provided a myofascial link from the abdominal wall to the obturator fascia: internal oblique and transverse aponeurosis, that blend into each other at the pubic symphysis, forming the urogenital diaphragm —> central tendon of perineum —> levator ani. From the levator ani (i) superficial layer, above the levator ani, bends posteriorly, through the arcus tendinous levator ani —> obturator internus aponeurosis; (ii) through the levator ani → deep portion of the anococcygeal ligament presacral fascia —> iliac fascia of the iliopsoas; (iii) deep layer, below the levator ani, connects the aponeurosis of the internal oblique with the lower band of the pelvic diaphragm.
Anterior and posterior pararenal spaces
As the kidneys are retroperitoneal they are behind the outer (parietal) layer of the peritoneum separated from it by the anterior renal fascia/toldt's fascia. 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: lateroconal fascia.
Posteriorly: anterior renal fascia/toldt's 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 presacral fascia (Muntean 1999) in the pelvis.
Toldt's fascia (Liang et al 2018)
Toldt's fascia fuses the overlying mesocolon to the underlying retroperitoneum. Therefore it utilises the term 'mesofascial interface' and 'retrofascial interface'. At the level of the kidney the floor of Toldt's fascia fuses with the anterior (Gerota) fascia and then extends in all directions:
Superiorly: dorsal surface of the duodenum and pancreas.
Medially: fuses with the adventitia of the abdominal aorta.
Laterally: tapers at an area below the reflection of the visceral and parietal peritoneum.
Inferiorly: as a combined fascia with the anterior renal fascia extends down covering the gonadal vessels, ureter and retroperitoneal structures as well as the upper end of the rectum where it meets the junction of the endopelvic fascia and proper fascia of the rectum.
Superior mesenteric artery
The superior mesenteric artery is an important landmark for the anterior renal fascia, root of the mesentery, transverse mesocolon 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).
Suh et al (2013) noted the movement of the superior mesenteric artery during expiration. These authors found the movement of the artery to be dependent upon the movement of the viscera during respiration.
Although the mesentery will obviously move during respiration could the movement of the superior mesenteric artery, as the point of attachment for the mesentery, play an important role in the mesentery’s mechanical movement?
Suh et al (2013) found on expiration due to movement of the pancreas, kidneys and duodenum the superior mesenteric artery translates superiorly and posteriorly. This translation occurs in respect to its origin at the abdominal aorta as the aorta is relatively fixed, in other words the superior mesenteric artery and abdominal aorta don't move as a single complex. This superior and posterior translation movement causes and upward angling and increase curvature of the superior mesenteric artery.
Mean time the branch* of the superior mesenteric artery moves left whilst the bifurication* moves right and the distance between the branch and the bifurication decreases.
*: these authors defined the branch of the superior mesenteric artery as being the point from which it branches from the abdominal aorta. The bifurication is a bit further along the artery where the first bifurication occurs on the branch vessel.
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