Anatomy of the Abdominal Cavity and Peritoneum

Overview of the Abdominal Cavity

The abdomen lies below the thoracic cavity and is divided into two sections: the abdominal cavity proper and the true (or lesser) pelvis. The abdominal cavity is bounded superiorly by the diaphragm and inferiorly by the inlet of the lesser pelvis. The dimensions of the abdomen can vary significantly due to factors such as organ distension, respiratory movements, the strength of the abdominal muscles, and the body's position.

Planes of the Abdomen

The abdomen is divided into nine regions utilizing specific planes:

  1. Transpyloric plane (at the 1st lumbar vertebra or tips of the 9th costal cartilages) traverses several key structures, including the pylorus, beginning of the duodenum, fundus of the gallbladder, and hilum of the kidney.

  2. Subcostal plane (located at the 3rd lumbar vertebra) and intertubercular plane (at the 5th lumbar vertebra) help delineate the boundaries of the abdominal cavity.

  3. Lateral vertical planes (midclavicular lines) further segment the cavity into distinct regions: Right hypochondrium, Epigastrium, Left hypochondrium, Right lumbar, Umbilical, Left lumbar, Right iliac, Hypogastrium, and Left iliac.

Peritoneal Cavity and Mesenteries

The peritoneal cavity comprises two sacs:

  • Greater Sac: This forms most of the peritoneal cavity and gets subdivided into supracolic and infracolic compartments. The supracolic compartment is located above the transverse colon while the infracolic compartment lies behind and below it.

  • Lesser Sac: A smaller pouch located behind the stomach, connecting to the greater sac through the epiploic foramen (or foramen of Winslow).

Peritoneal Folds and Ligaments

Peritoneal folds connect abdominal organs to each other or to the abdominal wall. The main folds include:

  1. Lesser Omentum: Connects the stomach to the liver.

  2. Greater Omentum: Connects the stomach to the transverse colon.

  3. Gastrosplenic Omentum: Between the stomach and spleen.

Ligaments include the falciform ligament (connects the liver to the anterior abdominal wall) and various other ligaments associated with the liver and diaphragm, such as the coronary ligament and triangular ligaments.

Functions of the Peritoneum

The peritoneum serves multiple functions, including:

  1. Providing a smooth surface facilitating movement of the viscera.

  2. Secreting peritoneal fluid which contains antibodies, thereby preventing infections.

  3. Assisting in wound healing through the transformation of mesothelial cells.

  4. Acting as a "police man of the abdomen" by localizing infections through the greater omentum.

  5. Serving as storage for fat, particularly within the greater omentum.

Clinical Significance of Peritoneal Spaces

Key peritoneal spaces include:

  1. Hepatorenal Pouch (Morison's pouch): A common site for fluid accumulation, particularly in cases of ascites or infection.

  2. Rectouterine and Rectovesical Pouches: These areas can also accumulate fluid and are important in the context of abdominal pathology, particularly in clinical evaluations.

Understanding these anatomical features, planes, and spaces provides crucial insights into both the structure and clinical implications of the abdominal cavity and peritoneum. Familiarity with these concepts is essential for effective diagnosis and treatment in clinical settings.

Clinical Case 1

A 57-year-old male presents with severe abdominal pain and fever. Upon examination, you note tenderness in the right upper quadrant. An ultrasound reveals fluid accumulation in the hepatorenal pouch. What is the most likely diagnosis?

  1. Gastric ulcer

  2. Cholecystitis

  3. Ascites

  4. Pancreatitis

  5. Appendicitis
    Answer: 2. Cholecystitis

Clinical Case 2

A 34-year-old female who is 28 weeks pregnant complains of abdominal pain localized to the suprapubic region. Imaging indicates fluid in the rectouterine pouch. Which of the following conditions could explain her symptoms?

  1. Ectopic pregnancy

  2. Ovarian cyst rupture

  3. Appendicitis

  4. Gastritis

  5. Urinary tract infection
    Answer: 2. Ovarian cyst rupture

Clinical Case 3

A 40-year-old man presents with jaundice and dark urine. His abdominal exam reveals an enlarged liver, and imaging shows a mass in the liver. Which structure is likely affected given the surrounding abdominal structures?

  1. Lesser omentum

  2. Greater omentum

  3. Peritoneal cavity

  4. Inferior vena cava

  5. Diaphragm
    Answer: 1. Lesser Omentum

Clinical Case 4

A 65-year-old female with a history of liver cirrhosis presents with severe abdominal swelling. Paracentesis reveals cloudy fluid with elevated white blood cell count. What is the most likely underlying condition?

  1. Peritoneal carcinomatosis

  2. Spontaneous bacterial peritonitis

  3. Pancreatic fluid collection

  4. Bowel obstruction

  5. Ascites
    Answer: 2. Spontaneous bacterial peritonitis

Clinical Case 5

A 25-year-old male presents with intense abdominal pain and distension. A CT scan shows evidence of multiple free air pockets. What is the most likely cause for this presentation?

  1. Perforated bowel

  2. Abdominal abscess

  3. Intestinal obstruction

  4. Gastric atony

  5. Cholecystitis
    Answer: 1. Perforated bowel

Clinical Case 6

A 45-year-old woman presents with pain in the right lower abdomen after eating spicy food. An ultrasound reveals inflammation in the right iliac region. What is the most likely diagnosis?

  1. Meckel's diverticulitis

  2. Appendicitis

  3. Ovarian torsion

  4. Gastritis

  5. Diverticulitis
    Answer: 2. Appendicitis

Clinical Case 7

A 60-year-old man with a long-standing history of diabetes presents with unexplained weight loss and abdominal distension. Imaging reveals dilated loops of bowel. Which peritoneal space is likely involved?

  1. Hepatorenal pouch

  2. Greater sac

  3. Lesser sac

  4. Rectouterine pouch

  5. Paravesical space
    Answer: 2. Greater sac

Clinical Case 8

An 8-year-old female presents with abdominal pain, fever, and vomiting. Upon examination, her abdomen is tender with rebound tenderness in the right lower quadrant. What is the most likely condition?

  1. Gastroenteritis

  2. Appendicitis

  3. Diverticulitis

  4. Mesenteric adenitis

  5. Pancreatitis
    Answer: 2. Appendicitis

Clinical Case 9

A 52-year-old woman presents with acute abdominal pain and nausea after binge eating. A CT scan shows thickening of the gallbladder wall. What condition should be highly suspected?

  1. Cholecystitis

  2. Gastric ulcer

  3. Biliary colic

  4. Pancreatitis

  5. Gastroenteritis
    Answer: 1. Cholecystitis

Clinical Case 10

A 33-year-old man presents with sudden onset of severe abdominal pain radiating to the back. He has a history of alcohol abuse. Which anatomical region should be evaluated for fluid collection?

  1. Hepatorenal pouch

  2. Rectovesical pouch

  3. Lesser sac

  4. Right iliac fossa

  5. Paraduodenal fossa
    Answer: 3. Lesser sac

Clinical Case 11

A 48-year-old female patient is diagnosed with Crohn's disease. During a follow-up, she reports new onset of pain localized in the right lower quadrant. What complication should be considered?

  1. Bowel obstruction

  2. Pancreatitis

  3. Perforated diverticulum

  4. Appendicitis

  5. Early bowel cancer
    Answer: 1. Bowel obstruction

Clinical Case 12

A 30-year-old pregnant woman reports severe nausea and abdominal pain in the first trimester. An ultrasound reveals a cystic mass in the right adnexa. What is the most likely diagnosis?

  1. Ovarian cancer

  2. Ectopic pregnancy

  3. Functional ovarian cyst

  4. Appendix mass

  5. Ovarian torsion
    Answer: 3. Functional ovarian cyst

Clinical Case 13

A 72-year-old man is admitted with confusion and hypotension. His abdominal exam shows mild distension. Which peritoneal space is the most likely location for fluid accumulation?

  1. Lesser sac

  2. Greater sac

  3. Hepatorenal pouch

  4. Rectouterine pouch

  5. Vesicouterine pouch
    Answer: 3. Hepatorenal pouch

Clinical Case 14

A 29-year-old female with a history of recurrent abdominal pain is found to have multiple fibroids upon examination. What possible effects might these have on the peritoneal cavity?

  1. Fluid accumulation

  2. Increased peritoneal function

  3. Decreased mobility of organs

  4. Bowel obstruction

  5. All of the above
    Answer: 5. All of the above

Clinical Case 15

An elderly female presents with sudden worsening abdominal distension and pain. Imaging reveals a volvulus of the sigmoid colon. Which part of the peritoneum is likely involved?

  1. Lesser omentum

  2. Falciform ligament

  3. Greater omentum

  4. Mesentery

  5. Diaphragm
    **Answer: 4. Mesentery