09A Abdominal Wall & Viscera

Lecture 09A: Abdominal Wall & Viscera

Learning Objectives

  • Explain inguinal canal variations by sex associated with developmental anatomic changes that occur during testicular and ovarian descent.

  • Describe the anatomic pathology and consequences of adhesions, cryptorchidism, and hydrocele.

Inguinal Hernias

Structure Overview

  • Male Structures:

    • Primary structure: Spermatic cord

    • Nerve:

    • Ilioinguinal nerve (enters canal partway, exits through superficial ring)

    • Genital branch of genitofemoral nerve (within spermatic cord), lymphatics, cremasteric vessels.

  • Female Structures:

    • Primary structure: Round ligament of uterus

    • Nerve:

    • Ilioinguinal nerve

    • Genital branch of genitofemoral nerve (accompanies round ligament), lymphatics.

Inguinal Canal

  • Description:

    • Oblique passage in lower anterior abdominal wall that serves as a connection between the abdominal cavity and external genitalia.

    • Extends from deep inguinal ring to superficial internal ring, parallel to the inguinal ligament.

    • Approximately 4 cm in length in adults.

  • Boundaries:

    • Anterior wall: External oblique aponeurosis and lateral contribution from internal oblique muscle.

    • Posterior wall: Transversalis fascia with medial contribution from conjoint tendon.

    • Conjoint tendon: Composed of fibers from internal oblique and transversus abdominus muscles.

    • Roof: Arching fibers of transversus abdominus and internal oblique muscles.

    • Floor:

    • Inguinal ligament and lacunar ligament (medially).

      • Inguinal ligament: Extends from anterior superior iliac spine to pubic tubercle.

      • Lacunar ligament: Triangular ligament extending from inguinal ligament to pubic tubercle.

Inguinal Hernia Types

  • Indirect Inguinal Hernia:

    • Pathway: Protrudes through the deep inguinal ring.

    • Commonality: Most common type, especially in men.

    • Nature: Congenital; lateral to inferior epigastric vessels; processus vaginalis remains open and protrudes through the inguinal canal into the scrotum or labia majora.

  • Direct Inguinal Hernia:

    • Pathway: Occurs through the posterior wall of the inguinal canal.

    • Commonality: Acquired; develops as the abdominal wall weakens with age.

    • Location: Medial to inferior epigastric vessels; may exit through superficial inguinal ring; does not traverse the entire inguinal canal; contents can extend into the scrotum.

Complications of Inguinal Hernias

  • Bowel entrapment: Bowel and fat can get stuck, leading to pain and bowel obstruction.

  • Strangulation:

    • The blood supply to the entrapped bowel is cut off, which can lead to ischemia.

Inguinal Hernia Physical Exam

  • Palpation Technique:

    • Locate the superficial inguinal ring superomedial to the pubic tubercle.

    • Finger invagination: Invaginate the scrotal skin with your index or little finger, advancing upward along the inguinal canal toward the superficial ring.

    • Fingertip should lie beneath external oblique aponeurosis at superficial inguinal ring level.

    • Cough or Valsalva maneuver:

    • Indirect hernia: Feel an impulse at fingertip as the hernia sac passes down the inguinal canal toward the scrotum.

    • Direct hernia: Feel a broad, pushing impulse on the fingertip as the hernia bulges directly through Hesselbach’s triangle into the posterior wall of the canal.

Bilateral Female Indirect Inguinal Hernias

  • Information not explicitly described but indicates the prevalence or occurrence in the female population.

Inguinal Hernia Repair

  • Before Repair Structure Assessment:

    • Anatomical Components:

    • Internal spermatic fascia, inguinal ligament, origin of cremasteric muscle, inguinal falx (conjoint tendon), external spermatic fascia, peritoneum, transversalis fascia, transversus abdominis muscle, internal oblique muscle, external oblique muscle, testicular artery and veins, ductus deferens, cremasteric muscle and fascia, internal spermatic fascia, spermatic cord, external spermatic fascia, testis.

  • Post-surgical anatomy remains largely similar but aims for restoration of integrity to the inguinal canal and alleviation of symptoms.

Relevant Clinical Scenario: Hernia Diagnosis Test

  • Scenario: A 64-year-old man presents with a painless right groin swelling gradually increasing in size over the past year. Upon examination:

    • Finger placed through the superficial inguinal ring while patient coughs leads to a broad impulse felt medially to the inferior epigastric vessels.

  • Diagnosis Options:
    A. Direct inguinal hernia – through Hesselbach’s triangle
    B. Indirect inguinal hernia – through Hesselbach’s triangle
    C. Direct inguinal hernia – through the deep inguinal ring
    D. Indirect inguinal hernia – medial to inferior epigastric vessel.

Testicular Pathology

Congenital Inguinal Hernia

  • Definition: The processus vaginalis precedes the descent of testes and should obliterate except for the tunica vaginalis around the testes.

    • Failure of Closure: Results in an indirect hernia.

Hydrocele

  • Definition: A collection of peritoneal fluid between the parietal and visceral layers of the tunica vaginalis.

  • Commonality: Common in newborns, most resolve spontaneously by age 2.

  • Complications: Very large hydroceles can cause discomfort, difficulty with mobility or hygiene, and rarely become infected; they may mask underlying testicular pathology.

    • Communicating Hydroceles: Have a connection to peritoneum.

    • Noncommunicating Hydroceles: No connection to peritoneum, fluid comes from mesothelial lining of tunica vaginalis.

  • Surgical Interventions:

    • Hydrocelectomy (excision or eversion of tunica vaginalis) for symptomatic, large, or cosmetically concerning cases.

    • Aspiration ± sclerotherapy is less favorable due to higher recurrence rates.

    • Secondary hydroceles should address underlying causes (e.g., infection, trauma, tumor).

Cryptorchidism

  • Definition: Incomplete descent of the testicles through the inguinal canal into the scrotum.

  • Prevalence: Occurs in 2-5% of full-term male infants and approximately 30% of premature male infants.

  • Clinical Features:

    • An empty, hypoplastic, or poorly rugated scrotum or hemiscrotum.

  • Management:

    • Most testicles descend within the first four months of life; if not, generally require surgical placement (orchidopexy).

  • Potential Complications:

    • Inguinal hernia, increased risk of testicular torsion and trauma, subfertility, malignant transformation of non-descended testes.

Learning Objectives

  • Identify the structural components of the abdominal region, including the diaphragm, greater and lesser omenta, mesenteries, and ligaments, and discuss their contribution to hiatal and diaphragmatic hernias.

  • Describe the courses of vessels, lymphatics, and nerves supplying the stomach.

  • Describe gastric cell types and their contribution to digestive function.

Peritoneal Cavity

Structure and Function

  • Components: Contains omenta, mesenteries, ligaments, blood vessels, and nerves that maintain the proper position of the viscera.

  • Structure: Composed of:

    • Visceral and Parietal Peritoneum.

    • Mesentery.

    • Retroperitoneum.

Subdivisions

  • Greater Sac:

    • Majority of peritoneal cavity; begins at diaphragm and ends in pelvic cavity.

  • Lesser Sac (Omental Bursa):

    • Smaller subdivision located posterior to the stomach and liver, continuous with the greater sac through the omental foramen.

  • Omental Foramen: Surrounded by the portal vein, hepatic artery, bile duct, inferior vena cava, caudate lobe of the liver, first part of the duodenum.

Greater Omentum

  • Description:

    • A double visceral peritoneal sheet comprised of 4 simple squamous mesothelial layers that attaches at the greater curvature of the stomach and duodenum.

    • Drapes over the transverse colon, jejunum, and ileum.

  • Function:

    • Fenestrated endothelium absorbs peritoneal fluid.

    • Circulates B and T lymphocytes and macrophages to destroy pathogens.

    • Responds to inflammation by encasing the affected area.

    • Rich blood supply contributing to neovascularization of ischemic tissues.

    • Tissue secretes growth factors that promote capillary sprouting and endothelial proliferation in adjacent ischemic tissues.

Lesser Omentum

  • Description:

    • Composed of double layers of peritoneum extending from the lesser curvature of the stomach and first part of the duodenum to the liver.

    • Forms anterior boundary of the lesser sac (omental bursa).

  • Function: Serves to stabilize upper abdominal viscera, encasing vessels, ducts, and nerves as they travel between the stomach and duodenum.

Ligaments Contributing to Lesser Omentum

  • Medial hepatogastric ligament: Passes between the stomach and liver.

  • Lateral hepatoduodenal ligament: Passes between the duodenum and liver.

Mesenteries

  • Described as peritoneal folds that attach viscera to the posterior abdominal wall.

  • Types of Mesenteries:

    • Fan-shaped, double-layered structure connecting jejunum and ileum to the posterior abdominal wall containing superior mesenteric vessels, lymphatics, and autonomic nerves.

    • Transverse mesocolon: Connects transverse colon to the posterior abdominal wall and separates supracolic and infracolic compartments.

    • Sigmoid mesocolon: Inverted, S-shaped fold attaching the sigmoid colon to the posterior abdominal wall.

Clinical Scenario: Omentum Function Test

  • Knowledge Check: Determining the primary function of the greater omentum with multiple-choice responses.

Diaphragm

Structure

  • Diaphragmatic Crus: Leg-like attachment wrapping around the aorta.

  • Central Tendon: Joins muscle to muscle with no bony attachment.

  • Arcuate Ligaments:

    • Median Arcuate Ligament: Involves the abdominal aorta.

    • Medial Arcuate Ligament: Related to psoas major muscle.

    • Lateral Arcuate Ligament: Related to the quadratus lumborum muscle.

Congenital Diaphragmatic Hernias

  • Definition: Developmental defect in the diaphragm allowing abdominal viscera to herniate into the thoracic cavity, impairing lung development.

  • Consequences:

    • Compression of developing lungs leads to pulmonary hypoplasia, resulting in severe postnatal respiratory distress.

    • Left-sided defects are more prevalent due to delayed closure of the left pleuroperitoneal chest and liver protection on the right side.

Diaphragm Developmental Timeline

  1. Weeks 3-4: Mesoderm condenses to form septum transversus.

  2. 5th week: Pleuroperitoneal membranes grow from the 12th rib anteriorly.

  3. 6-7th week: Pleuroperitoneal membranes fuse with septum transversum and mesoesophagus.

  4. Weeks 6-10: Myoblasts migrate into fused membranes, forming the muscular diaphragm.

  5. Septum transversum contributes to the central tendon of the diaphragm.

Bochdalek Diaphragmatic Hernia

  • Prevalence: ~85% of cases.

  • Location: Posterolaterally, usually on the left.

  • Result: Herniation of abdominal contents into thorax causing lung hypoplasia.

Morgagni Diaphragmatic Hernia

  • Prevalence: ~2-5% of cases.

  • Cause: Failure of sternal and costal fiber fusion, often on the right side; less severe and sometimes asymptomatic.

Symptoms of Intrapleural Intestines

  • Underdevelopment of lungs with diminished bronchial and arterial branching, leading to respiratory distress shortly after birth.

  • Examination findings: Absent breath sounds ipsilaterally, displaced PMI due to mediastinal shift, scaphoid abdomen; potential increased pulmonary hypertension risk.

Esophagus

Structure Overview

  • Adventitia: Outermost layer composed of loose connective tissue; does not contain serosa.

  • Muscularis Interna: Outer longitudinal and inner circular layers provide peristaltic movement and sphinter functions, transitioning from voluntary to involuntary control.

  • Esophageal Wall Muscle Composition:

    • Upper 1/3: Striated muscle under voluntary control.

    • Middle 1/3: Mixed muscle type (skeletal and smooth).

    • Lower 1/3: Smooth muscle only, under autonomic control.

  • Submucosa: Contains mucus glands for lubrication.

  • Mucosa: Composed of non-keratinized stratified squamous epithelium.

Z-line (Squamocolumnar Junction)

  • Definition: Visible transition area where non-keratinized stratified squamous epithelium of the esophagus changes to simple columnar epithelium of the gastric cardia.

  • Above Z-line: Stratified squamous epithelium for mechanical protection.

  • Below Z-line: Simple columnar epithelium containing mucus-secreting cells for protection against stomach acid.

Arterial Supply of Esophagus

  • Cervical Esophagus: Branches of inferior thyroid artery.

  • Thoracic Esophagus: Aortic esophageal arteries.

  • Abdominal Esophagus & LES: Supplied by left inferior phrenic artery and left gastric artery.

Venous Drainage of Esophagus

  • Cervical esophagus drains into inferior thyroid vein.

  • Thoracic esophagus drains into the azygos system.

  • Abdominal esophagus drains into left gastric vein (portal circulation).

Lymphatic Drainage of Esophagus

  • Cervical esophagus: Deep cervical and paratracheal lymph nodes.

  • Thoracic esophagus: Superior and posterior mediastinal lymph nodes.

  • Abdominal esophagus: Superior diaphragmatic, gastric, and celiac lymph nodes.

Innervation of Esophagus

  • Anterior and posterior vagal nerves enter the abdominal cavity with the esophagus, affecting both motor and sensory functions.

    • Anterior trunk: Supplies the anterior stomach wall and lesser curvature.

    • Posterior trunk: Supplies the posterior wall, fundus, and greater curvature.

  • Enteric Nervous System: Intrinsic neurons modulating GI tract functions, the myenteric plexus controls peristalsis.

Esophageal Pathology

  • Hiatal Hernias:

    • Type I (Sliding): Most common (~95%); gastric cardia slides through esophageal hiatus, associated with GERD.

    • Type II (Paraesophageal): Less common (<5%); gastric fundus displaced but squamocolumnar junction remains in place.

Barrett’s Esophagus

  • Definition: Metaplastic changes in distal esophageal mucosa from chronic gastroesophageal reflux.

  • Risk: Considered premalignant; increased risk for esophageal adenocarcinoma.

  • Management: Control GERD and monitor changes via biopsies, intervention for dysplastic changes.

  • Pathophysiology: Chronic acid exposure leads to intestinal metaplasia in response to injury, which can progress to neoplasia.

Stomach

Gastric Anatomy Overview

  • Cardia: Surrounds the esophagus' opening; secretes mucus and bicarbonate.

  • Fundus: Reservoir for ingested food; secretes hydrochloric acid, intrinsic factor, and pepsinogen.

  • Body: Main site for secretion and digestion processes.

  • Antrum: Distal stomach; secretes mucus and gastrin.

  • Pylorus: Contains pyloric sphincter regulating gastric emptying.

Gastric Histology

  • Mucosa: Comprising epithelium, lamina propria, and muscularis mucosae; protects from acid.

  • Cells:

    • Parietal Cells: Secrete HCl and intrinsic factor; stimulated by vagus, gastrin, and histamine.

    • Chief Cells: Secrete pepsinogen and gastric lipase; activated in acidic pH.

    • G-Cells: Release gastrin, stimulating HCl secretion and mucosal growth.

    • D-Cells: Secrete somatostatin to inhibit gastric secretion processes.

Gastric Secretion Regulation

  • Alkaline Tide: Temporary blood pH rise due to bicarbonate secretion from parietal cells during HCl formation.

  • Mechanoreceptors activated by stomach distention trigger vagovagal reflexes to stimulate peristaltic activity.

  • Sequence of regulation involving various gastric cells ensures coordinated secretion and digestion.

Blood Supply to Stomach

  • Celiac Trunk: Main arterial supply with branches including left gastric, splenic, and common hepatic arteries.

Venous Drainage of Stomach

  • Drains into portal circulation via left and right gastric veins, short gastric veins, and gastroepiploic veins.

Lymphatic Drainage

  • Lymph from gastric zones drains into celiac nodes.

Gastric Innervation

  • Sympathetic: Inhibits motility, pain response.

  • Parasympathetic: Stimulates secretory and motility functions via vagal influence.

Gastric Pathology

Peptic Ulcers

  • Definition: Mucosal defect due to acid exposure, commonly gastric (lesser curvature) or duodenal (first part of duodenum).

  • Etiology: Mainly due to Helicobacter pylori infections, chronic NSAID use.

  • Complications: Include bleeding, perforation, and potential malignancy.

  • Management: Involve PPIs, H2 blockers for acid suppression, and antibiotics for H. pylori.