Abdomen

Pain sensation arising from an internal organ travels with autonomic nerves and is usually dull and poorly localized. Intense visceral pain may be projected to the dermatome of the same spinal cord segment. This phenomenon is called ‘visceral referred pain’. The current working hypothesis for this phenomenon is that strong visceral pain afferents are ‘interpreted’ by our brain as originating from the afferent somatic input from the periphery (HEAD's zones) causing cutaneous hyperalgesia.

Examples: visceral pain from the stomach (peptic ulcer) is conveyed by the greater splanchnic nerve (T5–T9) and predominantly projects to the T8/T9 dermatome on the ipsilateral side.

T7–T11: thoracoabdominal nerves;

T12: anterior cutaneous branch of the subcostal nerve (T12);

L1: ilioinguinal nerve.

Note: the cutaneous innervation of the thorax region is shown in more details in chapter 5 (Thorax) .

See also chapter 12 (Neuroanatomy) for referred pain.

The anastomoses between superior and inferior epigastric arteries may serve as suitable bypass circulation for the perfusion of the lower extremities in cases of coarctation of the aorta (stenosis of the aortic isthmus, chapter 5 [Thorax], p. 273 ).

The internal thoracic (mammary) artery and the radial artery of the forearm may be used in bypass surgery in cases of myocardial infarction. The schematic to the right indicates potential anastomoses connecting the internal mammary arteries to the coronary arteries of the heart.

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Superficial anastomoses between SVC and IVC: epifascial abdominal veins from the paraumbilical region drain into the axillary vein via thoracoepigastric and lateral thoracic veins or into the femoral vein via superficial circumflex iliac and epigastric veins. Obstruction of the blood flow in the IVC may cause substantial dilation of the epifascial veins of the abdominal wall to facilitate venous drainage of the lower body.[ E273 ]

A complete physical exam includes the palpation of the superficial lymph nodes. Enlarged palpable lymph nodes may be a sign of an inflammatory reaction, a disease of the lymphatic system or a malignancy.

Lymph passes several consecutive lymph nodes before entering the venous system. Sentinal lymph nodes, the ‘guardian’ lymph nodes, are the first nodes a tumor drains to and are biopsied during cancer surgery for cancer staging. Cancer cells enter the node through one or more afferent lymphatic vessels. They may colonize the node and leave the node through the efferent vessels to spread to more distant regions of the body.

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^* Reticular cells lining the sinus wall also reside within the sinus.

The deep membranous layer of the subcutaneous tissue at the anterior abdominal wall (SCARPA’s fascia) is continuous inferiorly with the membranous layer of the perineal region (COLLES’ fascia). It does not continue to the fascia lata of the thigh. Thus fluids (extravasated urine, blood) collecting underneath the COLLES’ fascia can ascend to the anterior abdominal wall.

Abdominal surgical incisions:

Median or midline (dark blue) avoids nerves and blood vessels ( Fig. 6.4 ); may predistine to epigastric incisional hernias.

Pararectus (green) lateral to the rectus sheath.

Paramedian (red) rectus muscle is liberated from its sheath before posterior rectus sheath and peritoneum are opened.

Oblique and transverse: oriented to course of muscle fibers.

GRIDIRON (McBURNEY) (light blue): all abdominal muscle split with direction of muscle fibers; lateral one-third of the distance between ASIS and umbilicus.

Suprapubic (orange) (PFANNENSTIEL): pubic hairline; between inferior epigastric vessels.

Transverse (brown): through anterior rectus sheath and rectus abdominis muscle.

Subcostal (purple): 2.5 cm (1 in) below costal margin.

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The HESSELBACH’s triangle comprises a muscle-free area of the anterior abdominal wall and constitutes a weak area in the abdominal wall. The anterior abdominal wall deep to the membranous layer (SCARPA’s fascia of the subcutaneous abdominal tissue) here only consists of the transversalis fascia and the parietal peritoneum.

The cremasteric reflex is the contraction of the cremaster muscle and resulting elevation of the testicle on the same side when stroking the inside of the thigh. It is a physiological extrinsic reflex. The afferent fibers course in the femoral branch of the genitofemoral nerve (L1/L2) and the ilioinguinal nerve (L1), the efferent fibers project in the genital branch of the genitofemoral nerve.

Content of the spermatic cord:

• Vas deferens with artery of vas deferens (branch of the umbilical artery),

• Testicular artery (originates from the abdominal aorta),

• Pampiniform plexus of veins,

• Cremaster,

• Cremasteric artery (from the inferior epigastric artery),

• Genitofemoral nerve (genital branch) – innervation of cremaster,

• Lymph vessels,

• Autonomic nerves (testicular plexus).

Outside of the external spermatic fascia the ilioinguinal nerve passes through the superficial inguinal ring (sensory innervation of anterior scrotum – and labia majora in women).

Inguinal hernias always originate above the inguinal ligament and may reach into the scrotum in men or the labia majora in women. Indirect inguinal hernia (a) occur when content of the abdominal peritoneal cavity (greater omentum or intestinal loops) protrude into the inguinal canal or the scrotum. They are always positioned lateral to the inferior epigastric blood vessels (landmark!). Direct inguinal hernias (b) develop medial to the inferior epigastric blood vessels through the weak abdominal wall of HESSELBACH's triangle. In contrast, the hernial canal for femoral hernias is located inferior to the inguinal ligament (p. 296).

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Femoral hernias occur when content of the abdominal peritoneal cavity (greater omentum or intestinal loops) protrude into the femoral canal. The hernial canal for femoral hernias is located inferior to the inguinal ligament. Femoral hernias pass through the femoral ring and the femoral canal medial to the femoral vein and may surface through the saphenous opening of the fascia lata of the thigh. Femoral hernias are rare and occur more common in women than in men.

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Disturbances of the intestinal rotation can cause a malrotation (hyporotation and hyperrotation). These may result in intestinal obstruction (ileus) or an abnormal positioning of the respective intestinal segments, a condition that may impede the diagnosis of an appendicitis. A situs inversus describes a condition where all organs are positioned mirror-inverted. Examples for incomplete (a) and reversed (b) secondary gut rotations are shown.

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The parietal peritoneum (purple in figure) comprises the inner lining of the abdominal wall and is continuous with the visceral peritoneum (green in figure) to line the abdomino pelvic peritoneal cavity. The mesentery comprises a double layer of visceral peritoneum which ensheathes the abdominal viscera and folds back to the posterior abdominal wall. It contains blood and lymph vessels and autonomic nerves.

Intraperitoneal abdominal organs are completely covered by visceral peritoneum and have a mesentery: stomach, spleen, liver and gallbladder cecum with appendix vermiformis, small intestines (but only superior part of duodenum), transverse and sigmoid colon.

Extraperitoneal abdominal organs lack a mesentery and are positioned towards the posterior abdominal wall (retroperitoneal) or inferior to the peritoneal cavity (subperitoneal):

• Primary retroperitoneal organs: kidneys, ureters, adrenal glands;

• Secondary retroperitoneal organs have lost their dorsal mesentery by its fusion to the posterior abdominal wall during development: pancreas, duodenum (except for superior part) ascending and descending colon, upper two-thirds of rectum;

• Subperitoneal (infraperitoneal) organs: cervix of uterus, urinary bladder, distal ureter, vagina, prostate, seminal vesicles, lower one-third of rectum.

Intense localized pain (e.g. with appendicitis) in the abdomen indicates the involvement of the parietal peritoneum that is innervated by somatic nerves : thoracoabdominal nerves T7–T11, subcostal nerve (T12) and iliohypogastric and ilioinguinal nerves (L1). Rigidity of the abdominal muscles results from muscle contraction over the affected peritoneum as a protective reflex. In contrast, the pain afferents of the visceral peritoneum travel with the autonomic nerves and usually produce a dull pain that is not well localized.

The hepatorenal recess (MORRISON’s pouch), the posterior right infrahepatic space that belongs to the supracolic compartment, is an important peritoneal space in which fluids collecting in the peritoneal cavity (e.g. ascites) can ascend to the right subphrenic space (right subphrenic recess) below the diaphragm. The hepatorenal recess is bordered posteriorly by the right kidney and the right adrenal gland, anteriorly by the right lobe of the liver and the gall bladder and superiorly by the coronary ligament of the liver.

Similar to the other recesses of the peritoneal cavity, the omental bursa is of clinical relevance. Herniation of small intestinal loops (internal hernia), dissemination of malignant tumors (peritoneal carcinosis), or infections (peritonitis) c an involve the omental bursa. Peptic ulcers of the posterior wall of the stomach may perforate and cause peritonitis in the lesser sac. Inflammation or injuries to the pancreas may also cause fluid accumulation in the omental bursa.

Common surgical access routes to the omental bursa:

• 1. through the lesser omentum;

• 2. through the gastrocolic ligament;

• 3. through the transverse mesocolon.

The inferior recess of the omental bursa may extend further into the greater omentum in cases where the anterior and posterior folds have not fused.

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Anatomical constrictions of the esophagus

• 1.

  Cervical (pharyngoesophageal) constriction:

Level of C6, pharyngoesophageal junction caused by cricopharyngeus muscle, 15 cm (6 in) from incisors.

• 2.

  Thoracic (bronchoaortic) constriction:

Level of T4/T5, bronchoaortic constriction by arch of aorta, 22–23 cm (9 in) from incisors, visible in A/P views;

Level of T5, crossed by left main bronchus, 25–27 cm (10 in) from incisors, visible in lateral views.

• 3.

  Diaphragmatic constriction:

Level of T10, esophageal hiatus, 40 cm (16 in) from incisors.

For cervical esophageal diverticula see chapter 11 (Neck), p. 532.

If pressure in the portal venous system increases (portal hypertension), e.g. due to increased liver parenchymal resistance (cirrhosis of the liver), the venous blood is redirected to the superior vena cava and inferior vena cava via portocaval anastomoses. Clinically, the most important portocaval anastomosis is the connection of the esophagus to the gastric veins. This may result in dilations of the esophageal submucosal veins (esophageal varices). Rupture of these varices is associated with a mortality of approximately 50% and is, thus, the most frequent cause of death in patients with liver cirrhosis. Rupture into the lumen leads to the accumulation of darkened blood in the stomach, the rare external rupture results in bleeding into the peritoneal cavity.

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The lower esophageal sphincter (LES) is not a true sphincter muscle, but comprises a functional unit with several components:

Intrinsic components:

Esophageal muscle fibers with spiral orientation create longitudinal tension in the thoracic part and normally close the lumen. This intrinsic component is under neurohormonal influence. The lumen is widened locally with a peristaltic wave for the passage of food.

The esophageal submucosal venous plexus serves as mucosa cushion for a gas-tight closure of the lumen. The angle of 65° at the junction between cardia and fundus of the stomach is referred to as cardial notch ( angle of HIS ). This angulation creates a mucosal fold which helps prevent reflux of gastric content into the cardia.

Extrinsic components:

Phrenicoesophageal ligaments anchor the abdominal part of the esophagus to the diaphragm and secure its position at the esophageal hiatus. It allows the esophagus to move independently from the diaphragm during respiration and swallowing. The contractions of the diaphragm muscle serve as functional external sphincter to the esophagus related to the movement during respiration.

Insufficient lower esophageal sphincter components lead to gastroesophageal reflux disease (GERD) . Chronic acidic reflux causes inflammation of the esophageal mucosa and BARRETT’s esophagus with epithelial metaplasia of the lower esophagus. This increases the risk for esophageal cancer.

A hiatal gastric hernia (sliding hernia) occurs when parts of the stomach are pushed through a widened esophageal hiatus into the thoracic cavity. Heartburn is the most common symptom, similar to GERD. Chronically increased abdominal pressure or being overweight are common risk factors for GERD and hiatal hernia.

A sliding hiatal hernia is detected during the course of a radiocontrast examination. The arrow marks a stricture resulting from reflux esophagitis. The area below shows the hiatal sliding hernia of the stomach, as marked by the hollow arrow.

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