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Rectus Abdominis
Clinical Note
Surgical incisions through the rectus abdominis can be made transversely because the abdominal nerves run in that direction and the healed scar appears very similar to one of the many tendinous intersections within the muscle.
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The rectus sheath is composed of the aponeuroses of the abdominal muscles.
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The inguinal ligament (Poupart's) is the thickened inferior border of the external oblique aponeurosis.
Anterior Abdominal Wall Muscles
Clinical Note
Because of the dense fascia investing the rectus muscles, a rectus sheath hematoma, which may occur after muscle injury in a patient with coagulopathy, develops within a tight, nonelastic space and can become remarkably firm.
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The linea alba is composed of the interweaving fibers of the aponeuroses of the abdominal muscles and is important surgically because longitudinal incisions in it are relatively bloodless.
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The composition of the anterior and posterior layers of the rectus sheath changes superior and inferior to the arcuate line (of Douglas), which is where the inferior epigastric artery enters the sheath.
Abdominal Wall, Superficial View
Clinical Note
Varicosity of the paraumbilical veins is associated with portal hypertension (often caused by cirrhosis) and is termed caput medusa . Varicosity of the thoracoepigastric vein is similarly associated with portal hypertension and also with increased pressure or obstruction in the IVC because blood from the lower body then uses this vein to return blood to the heart via the SVC.
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Abdominal wall collaterals join the internal thoracic (mammary) and lateral thoracic veins to return venous blood to the vena cava.
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The paraumbilical veins communicate with the portal vein via the vein in the ligamentum teres hepatis (round ligament of the liver).
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When pathology obstructs normal flow, collateral vessels may dilate and become tortuous as shown in this CT.
Inguinal Region
Clinical Note
When the bladder fills, it expands in the extraperitoneal space between the peritoneum and the abdominal wall. Thus, the bladder may be penetrated (suprapubic cystotomy) for removal of urinary calculi, foreign bodies, or small tumors without entering the peritoneal cavity.
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The inferior epigastric vessels are an important landmark for differentiating between indirect and direct inguinal hernias. Pulsations from the artery can be felt medial to the neck of an indirect hernia and lateral to the neck of a direct hernia.
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The inferior epigastric vessels enter the rectus sheath approximately at the arcuate line, which is where the formation of the sheath changes. Inferior to the line the aponeuroses of all of the abdominal muscles pass anterior to the rectus abdominis muscle whereas superior to the line, half of the aponeurosis of the internal oblique muscle and all of the aponeurosis of the transversus abdominis pass posterior to the rectus muscle.
Quadratus Lumborum
Clinical Note
Grey-Turner's sign, ecchymosis in the flank resulting from retroperitoneal hemorrhage (most often from hemorrhagic pancreatitis), occurs as the blood spreads from the anterior pararenal space to between the two leaves of the posterior renal fascia and subsequently to the lateral edge of the quadratus lumborum muscle.
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The quadratus lumborum muscle primarily laterally flexes the trunk when acting unilaterally.
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The quadratus lumborum muscle attaches to the 12th rib and thereby can act as an accessory respiratory muscle by allowing the diaphragm to exert greater downward force by preventing upward movement of the 12th rib.
Psoas Major
Clinical Note
A psoas abscess usually results from disease of the lumbar vertebrae, with the pus descending into the muscle sheath; it may cause swelling in the proximal thigh that refers pain to the hip, thigh, or knee. The infection is most commonly tuberculous or staphylococcal. Before the discovery of antibiotics, these infections were life threatening.
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The psoas major muscle is a primary flexor of the trunk.
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The psoas minor is an inconstant muscle that inserts onto the pubis; the major inserts onto the lesser trochanter.
Kidneys, Normal and Transplanted
Clinical Note
A transplanted kidney is typically placed in the pelvis and its associated artery is attached to the external iliac artery, although it may also be attached to the common iliac artery as shown in the MR image.
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Patency of the anastomosis (connection) of the iliac artery to the transplanted renal artery is demonstrated.
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The indication for kidney transplantation is end-stage renal disease (ESRD). Diabetes is the most common cause of ESRD, followed by glomerulonephritis.
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Potential recipients of kidney transplants undergo an extensive immunologic evaluation to minimize transplants that are at risk for antibody-mediated hyperacute rejection.
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The left kidney is the one preferred for transplant because of its longer vein compared to the right.
Abdominal Regions
Clinical Note
The umbilical region remains a region of abdominal muscle weakness after birth, and umbilical or paraumbilical hernias can develop at any age.
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Classically, the abdomen is divided into four quadrants defined by vertical and horizontal planes through the umbilicus. More recently, it has been divided into nine regions based on subcostal, transtubercular, and right and left lateral rectus (semilunar) planes.
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Note the greater height of the left colic (splenic) flexure compared to the hepatic flexure on the right.
Appendix
Clinical Note
Appendicitis is a common cause of acute abdominal pain, which usually begins in the periumbilical region and migrates to the right lower quadrant because of associated peritoneal irritation.
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Inspissated bowel contents may lead to development of an appendolith, which is a calcified concretion that may obstruct the proximal lumen of the appendix; stasis, bacterial overgrowth, infection, and swelling (i.e., appendicitis) may follow, as can eventual rupture.
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The appendix is highly variable in its location, including occasionally being posterior to the cecum (retrocecal).
Abdomen, Upper Viscera
Clinical Note
A collection of pus between the diaphragm and the liver is known as a subphrenic abscess and may be secondary to the following: (1) peritonitis following a perforated peptic ulcer, appendicitis, pelvic inflammatory disease, or infection subsequent to cesarean section; (2) trauma that ruptures a hollow viscus and contaminates the peritoneal cavity; (3) a laparotomy during which the peritoneal cavity is contaminated; and (4) a ruptured liver abscess. Treatment is placement of a drainage tube until the abscess heals.
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The right kidney is not apparent in this image because of the obliquity of the image (the plane of the “coronal” image is angled so that it passes anterior to the right kidney but through the left kidney).
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The vasa recta (terminal branches) of the superior mesenteric artery (SMA) supply loops of small bowel.
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The terminal or fourth segment of the duodenum is attached to the diaphragm by a variable band of smooth muscle known as the suspensory ligament of the duodenum (ligament of Treitz). It is not recognizable on CT images.
Omental Bursa, Oblique Section
Clinical Note
Ascites is an accumulation of excess fluid in the peritoneal cavity. The finding of a disproportionate amount of ascites in the bursa may help narrow the differential diagnosis to organs bordering the lesser sac.
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The omental bursa, also known as the lesser sac, is the portion of the peritoneal cavity that is directly posterior to the stomach.
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The only natural connection between the omental bursa and the remainder of the peritoneal cavity (greater sac) is the epiploic foramen (of Winslow).
Stomach, In Situ
Clinical Note
Adjustable gastric banding, or lap band surgery, is a form of restrictive weight loss surgery (bariatric surgery) for morbidly obese patients with a body mass index (BMI) of 40 or more. The gastric band is an inflatable silicone prosthetic device that is laproscopically placed around the fundus of the stomach to reduce the amount of food that can be ingested at any one time.
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The stomach is filled with whole milk in this patient, the fat content of which decreases the CT density of the stomach fluid in order to enhance contrast differences with other tissues, such as the stomach wall. Note that the pyloric valve is closed, as it is most of the time.
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The position of the stomach is variable in relation to the body habitus. This patient has an “orthotonic” stomach.
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The term gastric antrum is a clinical term referring to the distal part of the stomach immediately proximal to the pyloric valve (pylorus). Anatomically, this part of the stomach would be referred to as the gastric antrum.
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