Topographical Anatomy

6 Topographical Anatomy


6.1 Surface Anatomy, Topographic Regions, and Palpable Bony Landmarks



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A Surface anatomy of the female


a Anterior view; b Posterior view.



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B Surface anatomy of the male


a Anterior view; b Posterior view.




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D Back and gluteal regions


Posterior view.



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E Body surface contours and palpable bony landmarks of the trunk


a Anterior view; b Posterior view.


6.2 Location of the Abdominal and Pelvic Organs and their Projection onto the Trunk Wall



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A Regions of the anterior trunk wall


Three levels can be identified on the abdominal wall from above downward: the epigastrium, mesogastrium, and hypogastrium. Each level consists of three regions:


The median region of the epigastrium is the epigastric region. It is flanked laterally by the right and left hypochondriac regions.


The median region of the mesogastrium is the umbilical region, which is bounded laterally by the right and left lumbar regions.


The median region of the hypogastrium is the pubic region, which is flanked by the right and left inguinal regions. The pubic region is bounded inferiorly by the urogenital region.


The levels of the abdomen are defined by horizontal planes that are determined by palpable bony landmarks (see C).



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B Quadrants of the anterior trunk wall


The quadrants of the anterior trunk wall are centered on the umbilicus, which lies at the level of the L 3–4 vertebral body and are named right and left upper and lower quadrant (RUQ, LUQ, RLQ, LLQ).



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C Horizontal (transverse) planes in the anterior trunk wall


The anterior trunk wall is divided transversely by the following imaginary planes of section:


Xiphisternal plane: passes through the synchondrosis between the xiphoid process and body of the sternum.


Transpyloric plane: plane midway between the jugular notch of the sternum and the superior border of the pubic symphysis. Located at the level of the L 1 vertebra, it divides the anterior trunk wall into upper and lower halves. The pylorus of the stomach is generally located slightly below this plane.


Subcostal plane: passes through the lowest points of the costal arch of the tenth rib at the level of the L 2 vertebral body. It marks the boundary between the epigastrium and mesogastrium (see A).


Supracristal plane: usually passes through the body of the L 4 vertebra, connecting the highest points on the iliac crests.


Intertubercular plane: connects the iliac tubercles and passes through the L 5 vertebral body. The intertubercular plane marks the boundary between the mesogastrium and hypogastrium.


Interspinal plane: connects the two anterior superior iliac spines.


Note: The three upper planes are variable in their location, which depends on the position and shape of the thoracic cage. The key variables are respiratory position, age, sex, and constitutional type.



E Projection of anatomical structures in the abdomen and pelvis onto the vertebral column


The spinal notation refers to vertebral bodies.





































T 7


Superior border of the liver


T 12


Aortic hiatus


L 1


Transpyloric plane (generally the pylorus is at or below this plane)


Gallbladder fundus


Renal hilum


Superior part of the duodenum


Pancreas (neck)


Origin of the celiac trunk


Origin of the superior mesenteric artery


Attachment of the transverse mesocolon


Spleen (hilum)


L 1/2


Origin of the renal arteries


L 2


Duodenojejunal flexure


L 3


Origin of the inferior mesenteric artery


L 3/4


Umbilicus


L 4


Aortic bifurcation


L 5


Origin of the inferior vena cava from the common iliac veins


S 3


Upper (cranial) border of the rectum



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F Placement of surgical skin incisions in the anterior abdominal wall


Note: The periumbilical midline incision passes around the left side of the umbilicus to avoid cutting the remnant of the umbilical vein on the right side (the ligamentum teres of the liver, see p. 253). This umbilical vein remnant is generally but not always obliterated, and injury to the vessel, if it is still patent, may cause significant bleeding.


The McBurney incision is also called the gridiron incision because it changes direction in different planes of the trunk wall. The muscles of the trunk wall can be divided less traumatically by tailoring the direction of the cut to the prevailing fiber direction of the various muscle layers.


6.3 Topography of the Opened Peritoneal Cavity (Supracolic Part and Infracolic Part)




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B Dissection with the greater omentum reflected superiorly and the small intestine in situ


Anterior view. The greater omentum has been reflected superiorly, carrying with it the transverse colon, to demonstrate how the intraperitoneal part of the small intestine is framed by the colon segments. The transverse mesocolon divides the peritoneal cavity into a supracolic part and an infracolic part (see B, p. 208).


The large epithelial surface area of the peritoneum is important clinically:


With bacterial infection (caused by external trauma or the seepage of septic material from an inflamed appendix), pathogenic microorganisms can easily spread within the peritoneal cavity, where bacterial toxins are readily absorbed and carried into the bloodstream. As a result, bacterial peritonitis (inflammation of the peritoneum) generally constitutes a very serious and life-threatening condition.


Localized inflammations may result in peritoneal adhesions and scar tissue bands (see A).


The large surface area can be utilized for peritoneal dialysis in patients with renal failure: A dialysis solution instilled into the peritoneal cavity can absorb waste products from the blood through the peritoneum, allowing them to be removed from the body.


6.4 Drainage Spaces and Recesses within the Peritoneal Cavity



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A Drainage spaces and recesses within the peritoneal cavity


a Anterior view with the greater omentum and small intestine removed; preferred metastatic sites (see blue stars);


b Posterior wall of the peritoneal cavity, anterior view. The mesenteric roots and sites of organ attachment create partially bounded spaces (recesses or sulci). Peritoneal fluid released by the peritoneal epithelium (transudate) can flow freely within these spaces.



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B Upper abdomen


Anterior view of the upper abdomen; the liver has been lifted to better display the subhepatic recess. The arrow points to the omental foramen, the opening into and out of the omental bursa behind the lesser omentum.



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C Recesses in the posterior wall of the peritoneal cavity


Anterior view of a male abdomen and pelvis. Because the peritoneum extends between organs, it forms recesses and sulci (see also A). In a sense, the omental bursa may be considered the largest recess in the peritoneal cavity (see p. 368).


Note: The individual recesses are located between an organ and the wall of the peritoneal cavity or between organs. Freely mobile loops of the small intestine may become entrapped in these recesses (“internal hernia”) hindering the passage of the intestinal contents and potentially causing a life-threatening bowel obstruction (“mechanical ileus”).


6.5 Overview of the Mesenteries



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A Overview of the mesenteries with the greater omentum reflected superiorly and the small intestine removed


Anterior view. The transverse colon and greater omentum have been reflected superiorly and the intraperitoneal small intestine has been removed, leaving short stumps of jejunum and ileum. Three principal mesenteries are distinguishable in relation to the small and large intestine (the formation of the mesenteries is described on p. 42):


The mesentery of the small intestine (the mesentery proper)


The transverse mesocolon


The sigmoid mesocolon (called also the mesosigmoid)


The origins of the mesenteries are shown in B. Smaller mesenteries are found on the vermiform appendix (mesoappendix) and rarely the upper part of the rectum (mesorectum, see C).



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B Projection of the mesenteric roots onto the skeleton



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C Overview of the mesenteries* with the greater omentum removed


Anterior view. The mesenteries have been exposed by removing the stomach, jejunum, and ileum, leaving short stumps of small intestine. The liver has been reflected superiorly to display one part of the lesser omentum: the hepatoduodenal ligament, which connects the liver to the pylorus and duodenum. The other part of the lesser omentum, the hepatogastric ligament (peritoneal fold between the liver and lesser curvature of the stomach), has been removed with the stomach, opening the anterior wall of the omental bursa. Most of the transverse colon and sigmoid colon have been removed to display the roots of the transverse mesocolon and sigmoid mesocolon.


Note: The ascending and descending colon become attached to the posterior wall of the peritoneal cavity during the fourth month of embryonic development. The mesenteries of the ascending and descending colon become fused to the posterior wall of the peritoneal cavity. The transverse mesocolon crosses over the duodenum, whose mesentery also fuses to the posterior wall of the peritoneal cavity during embryonic development (see p. 46). The transverse mesocolon necessarily passes over this “retroperitoneal portion” of the duodenum because of its attachment to the posterior wall of the peritoneal cavity. Developmentally, almost all of the mesenteries are dorsal mesenteries. Only upper abdominal organs like the stomach and liver have ventral mesenteries.


* “Mesentery” in the broad sense refers to any of the peritoneal folds attached to the small and large intestine. “Mesentery” in the strict sense refers specifically to the mesentery of the jejunum and ileum, and consequently the terms “mesojejunum” and “mesoileum” are not used.


6.6 Topography of the Omental Bursa



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A Shape and location of the omental bursa in sagittal section


Left lateral view. The omental bursa is the largest potential space in the peritoneal cavity. It is located behind the lesser omentum and stomach. Note: As the stomach rotates during embryonic development, the omental bursa comes to lie posterior to the stomach. The pancreas, which migrates into the retroperitoneum secondarily, thus forms part of the posterior wall of the bursa, which provides a route for gaining surgical access to that organ. As the stomach rotates in the clockwise direction (viewed from the front), its lesser curvature points to the right and also superiorly, simultaneously displacing the liver superiorly and to the right. As a result of this, the omental bursa comes to lie partially posterior to the liver.


B Boundaries of the omental bursa

























Anterior


Lesser omentum, gastrocolic ligament


Posterior


Pancreas, aorta (abdominal part), celiac trunk, splenic artery and vein, gastropancreatic fold, left suprarenal gland, superior pole of left kidney


Superior


Liver (with caudate lobe), superior recess of omental bursa


Inferior


Transverse mesocolon, inferior recess of omental bursa


Left


Spleen, gastrosplenic ligament, splenic recess of omental bursa


Right


Liver, duodenal bulb


C Surgical approaches to the omental bursa (see A)



Through the omental foramen (natural opening, see E)


Between the greater curvature of the stomach and the transverse colon through the gastrocolic ligament


Through the transverse mesocolon after elevating the transverse colon (inferior approach)


Between the lesser curvature of the stomach and the liver (through the lesser omentum)



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D Omental bursa, anterior view


a Boundaries of the omental bursa, also the shape and location of the gastric bed


b Structure of the posterior wall of the omental bursa




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F Transverse section through the omental bursa


Schematic section through the abdomen at the T 12/L 1 level, viewed from below.


Note the walls and recesses that result from the formation of the bursa during the embryonic rotation of the stomach. Because the initial upper right portion of the embryonic body cavity moves posteriorly as part of the 90° rotation of the stomach, structures that were formerly posterior (spleen) move to the left side while structures that were formerly anterior (liver) move to the right side. Recesses in the omental bursa extend close to these organs (see B).


6.7 Topography of the Upper Abdominal Organs: Liver, Gallbladder, Duodenum, and Pancreas



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A Location of the liver and gallbladder


Anterior view, the stomach and small intestine have been removed, leaving a short stump of the jejunum. Most of the transverse colon has been removed. The liver has been lifted for better exposure of parts of the lesser omentum, hepatoduodenal ligament and pancreas (for the contents of the hepatoduodenal ligament see Eb).



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B Position of the liver


Transverse section through the abdomen at approximately the T 12/L 1 level, viewed from below. The liver is intraperitoneal except for the “bare area,” which is not visible here. The left lobe of the liver extends into the LUQ, where it is anterior to the stomach. The peritoneal fold between the liver and the lesser curvature of the stomach (lesser omentum) can be seen. Portions of the liver form the right boundary of the omental bursa.



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C Areas of contact with other organs


View of the visceral surface of the liver.


Note: Impressions from organs that are in direct contact with the liver are visible only on a liver that has been hardened in place by a chemical preservative (“fixation”). An unfixed liver from a cadaver that has not been chemically preserved is so soft that generally it will not show organ impressions. Diseases of the liver may easily spread to other organs, and vice versa, at areas of contact with adjacent organs (extensive owing to the size and topography of the liver).



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D Location of duodenum and pancreas


Anterior view; the liver, stomach and small intestine have been removed, leaving the duodenum and a very small stump of the jejunum. The ascending and transverse colon have been removed to expose the right kidney, pancreas, and duodenal loop. The secondarily retroperitoneal descending colon is left in situ. The pancreas and duodenum are also secondarily retroperitoneal (for peritoneal relationships see p. 209). Both kidneys and suprarenal glands, located in the retroperitoneal space, are visible through the parietal peritoneum. The kidneys and suprarenal glands are primarily retroperitoneal. The intraperitoneal spleen is located in the left upper quadrant in a compartment called the splenic niche.


Note: The root of the (intraperitoneal) transverse mesocolon crosses anterior to the duodenum and pancreas.



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E Peritoneal relationships of the duodenum and pancreas; Contents of the hepatoduodenal ligament


a Peritoneal relationships of the duodenum and pancreas, anterior view. The root of the transverse mesocolon crosses over the descending part of the duodenum and the pancreas.


b Contents of the hepatoduodenal ligament. The hepatoduodenal ligament is part of the lesser omentum and connects the liver with the pylorus and superior part of the duodenum. It contains the hepatic portal vein, the proper hepatic artery and the common bile duct.


6.8 Topography of the Upper Abdominal Organs: Stomach and Spleen



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A Location of the stomach and spleen


Anterior view. The liver and lesser omentum have been removed, the greater omentum has been opened and retracted to the left, and the stomach pulled slightly downward for better exposure. At several sites, the peritoneum has been removed or windowed for better exposure of the opening of the hepatic veins into the inferior vena cava and the opening of the veins of the stomach into the hepatic portal vein at the margin of the hepatoduodenal ligament (here completely opened).


The spleen is retracted from its “niche” and lies close to the fundus and greater curvature of the stomach. The intraperitoneal stomach covers most of the retroperitoneal pancreas. The greater omentum, a remnant of the dorsal mesogastrium, is suspended from the greater curvature of the stomach. The stomach is partially shown transparent to display the splenic artery that extends behind the stomach from the celiac trunk to the spleen.



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B Areas of contact with adjacent organs


a, b Anterior and posterior views of the stomach walls. Because the stomach is intraperitoneal, it is very mobile relative to adjacent organs. But since the stomach is in close contact with other organs, lesions that penetrate the stomach wall (ulcers, malignant tumors) may spread to nearby organs or may cause adhesions to develop between the stomach and adjacent organs.


Aug 4, 2021 | Posted by in GENERAL SURGERY | Comments Off on Topographical Anatomy
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