Abdominal Anatomy

RADT 1502: Radiographic Anatomy and Positioning I - Abdomen

Abdominal Cavity

• Largest Body Cavity: Comprises both the abdominal and pelvic cavities.
  • Separation: An imaginary line at the level of the anterior iliac crest separates the abdominal cavity from the pelvic cavity.
• Lining: Lined by the peritoneum, which is the largest serous membrane in the body.
  • Layers of Peritoneum:
    • Parietal Peritoneum: Lines the abdominal wall.
    • Visceral Peritoneum: Covers the organs within the abdominal cavity.
• Mesentery: A sheet of peritoneum attached to the large and small intestines.
  • Folds:
    • Greater Omentum: A large fold attached to the greater curvature of the stomach and transverse colon (dorsal mesentery origin).
    • Lesser Omentum: Connects the lesser curvature of the stomach and the liver (ventral mesentery origin), containing the portal triad.
  • Function:
    • Secretes fluid for lubrication.
    • Supports abdominal organs by holding them in place.
    • Provides protection to the organs.

Abdominal Cavity Anatomy: Retroperitoneum

• Definition: The cavity located behind the peritoneum.
• Structures within the Retroperitoneum:
  • SAD PUCKER Mnemonic: A common mnemonic to remember retroperitoneal organs:
    • Suprarenal (adrenal) glands
    • Aorta & inferior vena cava (IVC)
    • Duodenum (except the $1^{st}$ part)
    • Pancreas (head & body)
    • Ureters & bladder
    • Colon (ascending & descending)
    • Kidneys
    • Esophagus
    • Rectum (mid-distal)
• Primary Retroperitoneal: Organs that developed and remained outside the peritoneum.
• Secondarily Retroperitoneal: Organs that were initially intraperitoneal but migrated behind the peritoneum during development.

Abdominal Cavity Anatomy: Gastrointestinal System

• Small Intestine:
  • Duodenum: The first, shortest, and widest part of the small intestine, it is partially retroperitoneal.
  • Jejunum: The middle section, primarily intraperitoneal.
  • Ileum: The final section, primarily intraperitoneal, ending at the ileocecal valve.
• Large Intestine:
  • Cecum: A pouch connected to the junction of the small and large intestines, includes the appendix.
  • Ascending Colon: Travel upwards on the right side of the abdomen (retroperitoneal).
  • Transverse Colon: Extends across the upper abdomen (intraperitoneal).
  • Descending Colon: Travels downwards on the left side of the abdomen (retroperitoneal).
  • Sigmoid Colon: S-shaped segment connecting to the rectum (intraperitoneal).
  • Rectum: Final section of the large intestine.
  • Anus: The external opening of the rectum.

Abdominal Cavity Anatomy: Accessory Organs

• Liver:
  • Largest Gland in the Body.
  • Lobes: Right, Left, Caudate, Quadrate.
  • Vasculature:
    • Portal Vein: Carries nutrient-rich blood from the GI tract to the liver.
    • Hepatic Artery: Supplies oxygenated blood to the liver.
  • Functions:
    • Filters blood and produces hormones.
    • Produces bile to aid in fat digestion.
    • Stores glycogen.
    • Decomposes red blood cells.
• Biliary System - Gallbladder (GB):
  • Description: Pear-shaped sac located beneath the liver.
  • Function: Stores and concentrates bile produced by the liver.
• Pancreas:
  • Description: A posterior, elongated gland, mostly retroperitoneal.
  • Functions:
    • Endocrine: Produces hormones like:
      • Insulin (from beta cells): Anabolic hormone that lowers blood glucose.
      • Glucagon (from alpha cells): Catabolic hormone that raises blood glucose.
    • Exocrine: Produces pancreatic juice containing digestive enzymes:
      • Lipase (fat digestion).
      • Trypsin (protein digestion).
      • Amylase (carbohydrate digestion).
• Spleen:
  • Description: Bean-shaped organ located in the left upper quadrant (LUQ).
  • Functions:
    • Produces lymphocytes (white blood cells).
    • Stores and removes dead or dying red blood cells (RBC's).
    • Stores platelets.

Body Habitus and Organ Placement

• Body Habitus Influences Organ Position:
  • Hypersthenic: Large, broad body build. Organs like the stomach and gallbladder are higher and more transverse.
  • Asthenic: Slender, frail body build. Organs are lower and more vertical.

Abdominal Regions and Quadrants

• Nine Abdominal Regions (anatomical planes):
  • Upper Row:
    • Right Hypochondriac Region: Liver, Right Kidney, Gallbladder, Large/Small Intestine.
    • Epigastric Region: Liver, Stomach, Spleen, Duodenum, Adrenal Glands, Pancreas.
    • Left Hypochondriac Region: Liver's tip, Stomach, Pancreas, Left Kidney, Spleen, Large/Small Intestine.
  • Middle Row:
    • Right Lumbar Region: Ascending Colon, Small Intestine, Right Kidney.
    • Umbilical Region: Duodenum, Small Intestine, Transverse Colon.
    • Left Lumbar Region: Descending Colon, Small Intestine, Left Kidney.
  • Lower Row:
    • Right Iliac Region: Appendix, Cecum, Ascending Colon, Small Intestine.
    • Hypogastric Region: Bladder, Sigmoid Colon, Small Intestine, Reproductive Organs.
    • Left Iliac Region: Sigmoid Colon, Descending Colon, Small Intestine.
• Planes for Regions:
  • Subcostal Plane: Transverse plane immediately below the costal cartilages.
  • Intertubercular Plane: Transverse plane connecting the iliac tubercles.
  • Transpyloric Plane: Often at $L1$-$L2$, typically bisects the pylorus.
  • Transtubercular Plane: Often at $L5$, commonly aligned with the iliac tubercles.
• Four Abdominal Quadrants (clinical divisions by transumbilical plane):
  • Right Upper Quadrant (RUQ): Liver, Stomach, Gallbladder, Duodenum, Right Kidney, Pancreas, Transverse Colon, Right Adrenal Gland, Small Intestine.
  • Left Upper Quadrant (LUQ): Liver, Left Adrenal Gland, Stomach, Left Kidney, Pancreas, Spleen, Transverse Colon, Small Intestine.
  • Right Lower Quadrant (RLQ): Small Intestine, Large Intestine, Cecum, Appendix, Right Ureter, Right Reproductive Organs (ovary, fallopian tube, spermatic cord).
  • Left Lower Quadrant (LLQ): Small Intestine, Large Intestine, Left Ureter, Left Reproductive Organs (fallopian tube, ovary, spermatic cord), Sigmoid Colon.

Abdominal Radiographic Procedures

• Patient Preparation (for Fluoroscopy):
  • Controlled diet.
  • Laxative.
  • Enema.
  • Contraindications: Preliminary prep is never administered to acutely ill patients or those with visceral rupture, intestinal obstruction, or perforation.
• Common Routines:
  • KUB (Kidneys, Ureters, Bladder) or Supine Abdomen (AP Projection):
    • Can demonstrate free air (Rigler’s sign).
    • Centering: At the level of the iliac crests.
    • Evaluation Criteria: Area from pubic symphysis to upper abdomen included, centered vertebral column, no rotation, soft gray tones (many shades of gray).
  • AP Abdomen Upright:
    • Indications: Visualizes air/fluid levels.
    • Centering: If the bladder is to be included, center the IR at the level of the iliac crests. If not, CR is $2$ inches above iliac crests to include the diaphragm.
    • Evaluation Criteria: Similar to supine, focusing on air-fluid levels and inclusion of diaphragm if applicable.
  • PA Chest: Often performed in conjunction with abdominal series because it is more sensitive than an abdominal radiograph for picking up free air under the diaphragm.
    • Air escaping from the GI tract into the peritoneal space rises to the highest level, just beneath the diaphragm.
  • PA Projection Upright:
    • Benefit: Reduces gonadal dose compared to AP projection.
    • Procedure: Same centering and general procedure as an upright AP projection.
  • AP Projection L Lateral Decubitus:
    • Patient Position: Used for patients too ill to stand, lying on their left side.
    • Setup: Use a radiolucent pad to elevate the patient. Patient should lie on their side for several minutes to allow air/fluid levels to settle. Use a grid.
    • CR: $2$ inches above the iliac crests to include the diaphragm.
    • Suspension: Suspend at the end of expiration.
    • Evaluation Criteria: Both sides of the abdomen, no rotation/movement, proper markers.
    • Why Left Lateral?: The liver provides the density needed on the right side to show and outline free air against a solid background, differentiating it from air-filled colon loops.
  • Lateral Projection:
    • Purpose: Demonstrates the prevertebral space occupied by the abdominal aorta, and any intra-abdominal calcifications or tumor masses.
    • CR: Along the midcoronal plane, $2$ inches above the iliac crests to demonstrate the diaphragm.
    • Evaluation Criteria: Soft gray tones, no rotation.
• Technique Considerations:
  • More gray tones (long scale contrast) and less contrast are desired for abdominal radiographs to visualize various tissue densities.
  • This implies using a higher kVp and adjusting mAs accordingly to maintain appropriate density while achieving the desired contrast.

Pathology of the Abdomen

• Peritonitis:
  • Definition: Inflammation of the peritoneum, often caused by infection or irritation from leaked bodily fluids.
• Meconium Peritonitis:
  • Description: Occurs in utero from fetal bowel perforation and spillage of meconium (fetal stool) into the peritoneal cavity.
  • Radiographic Finding: Intraperitoneal meconium usually calcifies, sometimes within $24$ hours, visible on imaging.
• Hernia:
  • Definition: A bulge or protrusion of tissue and/or an organ through a weakened part of the muscular wall of the body that normally contains it.
  • Types of Hernias:
    • Epigastric Hernias
    • Incisional Hernias
    • Umbilical Hernias
    • Direct Inguinal Hernias
    • Indirect Inguinal Hernias
    • Femoral Hernias
    • Hiatal Hernias: Occur when the stomach protrudes through the esophageal hiatus of the diaphragm.
  • Emergency: Strangulated Hernia: A severe complication where the blood supply to the herniated viscus becomes so constricted by swelling and congestion that its circulation is arrested. This is a medical emergency requiring immediate intervention.
• Volvulus:
  • Definition: An abnormal twisting or torsion of a segment of the intestine, causing obstruction and impairment of normal blood flow. This is a medical emergency.
  • Common Sites: Small intestine, cecum, and sigmoid colon.
  • Clinical Signs: Sudden onset of abdominal pain, nausea, vomiting, blood in stool.
  • Treatment: Surgical intervention is usually required.
  • Consequences if Untreated: Gangrene (death of the GI tract segment), intestinal obstruction, perforation of the intestine, peritonitis.
  • Example: Sigmoid Volvulus:
    • Radiographic Findings: Distended loop of bowel in the RUQ with a