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Abdominal Wall, Mesentery, Peritoneum & Retroperitoneal Disorders

ABDOMINAL WALL AND UMBILICUS

Embryology

  • Origin: Abdominal wall develops from the lateral plate of embryonic mesoderm.
  • Layers:
    • Ectoderm (outer protective layer),
    • Endoderm (inner nutritive layer),
    • Mesoderm (middle layer).
  • Mesoderm differentiation:
    • Somatic layer: forms the abdominal wall.
    • Splanchnic layer: forms the viscera (muscle, blood vessels, lymphatics, connective tissues).
  • Development:
    • Abdominal wall forms an inverted U-shaped tube communicating with the extraembryonic coelom.
    • By the third month of gestation, the body wall closes except at the umbilical ring.

Anatomy

  • Abdominal Wall Layers:
    1. Skin
    2. Subcutaneous tissue (Camper’s fascia, Scarpa’s fascia)
    3. Superficial fascia
    4. External oblique muscle
    5. Internal oblique muscle
    6. Transversus abdominis muscle
    7. Transversalis fascia
    8. Preperitoneal adipose tissue
    9. Peritoneum
  • Subcutaneous Tissue:
    • Camper fascia: superficial adipose layer.
    • Scarpa fascia: deeper fibrous connective tissue aiding in skin approximation post-surgery.
  • Muscle and Investing Fasciae:
    • External oblique: Largest, originates from lower seven ribs, forms inguinal ligament (Poupart ligament).
    • Internal oblique: Opposite fiber direction to external oblique, forms part of the rectus sheath.
    • Transversus abdominis: Smallest, forms Hesselbach’s triangle (important for inguinal hernia repairs).

Rectus Abdominis Muscle

  • Structure:
    • Paired, flat muscles located on the anterior abdominal wall.
    • Separated by the linea alba.
    • Composed of long fascicles with tendinous inscriptions.
  • Function: Flexes the vertebral column, supports abdominal wall.
  • Rectus Sheath: Encloses the rectus abdominis, derived from the aponeuroses of the three flat abdominal muscles.

Preperitoneal Space and Peritoneum

  • Contents of Preperitoneal Space:
    • Inferior epigastric artery and vein.
    • Medial and median umbilical ligaments.
    • Falciform ligament (connects umbilicus to liver).

Vessels and Nerves of the Abdominal Wall

  • Vascular Supply:
    • Arteries: Last six intercostal arteries, four lumbar arteries, superior and inferior epigastric arteries, deep circumflex iliac arteries.
    • Venous Drainage: Above umbilicus (drains into superior vena cava), below umbilicus (drains into inferior vena cava).
    • Caput medusae: Dilated veins in portal hypertension, indicating portal venous obstruction.
  • Lymphatic Drainage:
    • Supraumbilical region: Axillary lymph nodes.
    • Infraumbilical region: Superficial inguinal lymph nodes.
    • Sister Mary Joseph nodule: Umbilical metastasis from intra-abdominal cancer.
  • Innervation:
    • Thoracic nerves (T7-T12): Motor and sensory innervation to abdominal wall.
    • Ilioinguinal and iliohypogastric nerves: Provide sensory innervation to lower abdomen and inguinal region, encountered during inguinal hernia repairs.

Abnormalities of the Abdominal Wall

Congenital Abnormalities

  • Umbilical Hernias: Classified into three forms:
    • Omphalocele:
      • Definition: Funnel-shaped defect in the central abdomen with viscera protruding into the base of the umbilical cord.
      • Cause: Failure of abdominal wall musculature to unite in the midline during fetal development.
      • Presentation:
        • Viscera covered only by peritoneum and amnion, not skin.
        • Umbilical vessels may be splayed over or pushed aside.
        • Larger defects may include liver and spleen within the cord.
      • Associated Anomalies:
        • 50–60% have other congenital anomalies (skeletal, GI, nervous, GU, cardiopulmonary systems).
    • Gastroschisis:
      • Definition: Congenital defect where the umbilical membrane ruptures in utero, allowing intestines to herniate outside the abdominal cavity.
      • Location: Almost always to the right of the umbilical cord.
      • Presentation:
        • Intestines not covered by skin or amnion.
        • Risk of mesenteric volvulus, leading to intestinal ischemia and necrosis.
      • Associated Anomalies:
        • Occur in about 10% of patients.
    • Infantile Umbilical Hernia:
      • Definition: Appears after the umbilical cord stump sloughs off.
      • Cause: Weakness between the scarred umbilical cord remnants and the umbilical ring.
      • Presentation:
        • Hernia covered by skin.
        • Occurs at the superior margin of the umbilical ring.
        • Becomes prominent when the infant cries.
      • Prognosis:
        • Most resolve within 24 months.
        • Strangulation is rare.
      • Treatment:
        • Surgical repair if persistent beyond age 3 or 4 years.
    • Acquired Umbilical Hernia:
      • Definition: Develops remote from the initial closure of the umbilical ring.
      • Cause: Weakening of the cicatricial tissue due to excessive stretching (e.g., pregnancy, labor, ascites).
      • Presentation:
        • Occurs at the upper margin of the umbilicus.
        • Does not spontaneously resolve; increases in size.
        • High risk of strangulation due to dense fibrous ring.
  • Persistence of the Omphalomesenteric Duct:
    • Meckel Diverticulum:
      • Definition: Persistence of the intestinal end of the duct, forming a true diverticulum from the antimesenteric border of the ileum.
      • Rule of 2s:
        • Found in 2% of the population.
        • Located within 2 feet of the ileocecal valve.
        • Approximately 2 inches in length.
        • Contains two types of ectopic mucosa (gastric and pancreatic).
      • Complications:
        • Inflammation, perforation, hemorrhage, obstruction.
        • GI bleeding due to ectopic gastric mucosa causing peptic ulcers.
        • Obstruction from intussusception or volvulus.
    • Enterocutaneous Fistula:
      • Definition: Patent omphalomesenteric duct forming a fistula between the distal small intestine and umbilicus.
      • Presentation:
        • Passage of meconium and mucus from the umbilicus in newborns.
      • Risks:
        • Mesenteric volvulus.
      • Treatment:
        • Prompt laparotomy and excision of the fistula.
    • Umbilical Polyp:
      • Definition: Persistence of the distal duct as a mucosal remnant at the umbilicus.
      • Presentation:
        • Resembles an umbilical granuloma but does not respond to silver nitrate.
      • Treatment:
        • Excision of the mucosal remnant and any underlying duct or sinus.
    • Umbilical Sinus:
      • Definition: Persistence of the distal omphalomesenteric duct forming a sinus tract.
      • Diagnosis:
        • Sinogram to delineate the tract.
      • Treatment:
        • Excision of the sinus.
    • Omphalomesenteric Duct Cyst:
      • Definition: Mucus accumulation in a portion of the persistent duct.
      • Treatment:
        • Excision of the cyst and associated duct.
  • Persistence of the Allantois:
    • Anatomy: Allantois connects the urinary bladder with the umbilicus during development (urachus).
    • Abnormalities:
      • Vesicocutaneous Fistula:
        • Urine discharge from the umbilicus.
      • Urachal Cyst:
        • Presents as a lower abdominal mass.
      • Urachal Sinus:
        • Drainage of mucus from the umbilicus.
    • Risks:
      • Potential for malignant transformation.
    • Treatment:
      • Excision of the urachal remnant and bladder closure if needed.

Acquired Abnormalities

  • Diastasis Recti:
    • Definition: Thinning of the linea alba in the epigastrium.
    • Presentation:
      • Smooth midline protrusion of the abdominal wall.
      • Transversalis fascia is intact; not a true hernia.
      • Noticeable when straining or lifting the head.
    • Treatment:
      • Reassurance about its benign nature.
  • Anterior Abdominal Wall Hernias:
    • Epigastric Hernias:
      • Location: Through the linea alba where vessels and nerves perforate.
      • Presentation:
        • Small but can cause significant pain and tenderness.
      • Treatment:
        • Surgical closure of the fascial defect.
    • Spigelian Hernias:
      • Location: Region of the semilunar line.
      • Presentation:
        • Localized pain and tenderness.
        • Hernia sac often not palpable.
      • Diagnosis:
        • Ultrasonography or CT scan.
      • Treatment:
        • Surgical repair of the defect.
  • Rectus Sheath Hematoma:
    • Definition: Accumulation of blood within the rectus sheath.
    • Epidemiology:
      • More common in women and older adults.
      • Associated with anticoagulation therapy (70%), trauma, coughing, pregnancy.
    • Presentation:
      • Sudden abdominal pain, worsened by movement.
      • Tenderness over rectus sheath, possible abdominal mass.
      • Possible ecchymosis (Cullen and Grey Turner signs).
      • Hemodynamic instability is rare.
    • Diagnosis:
      • Ultrasound or CT scan confirms the hematoma.
    • Treatment:
      • Conservative management: Rest, analgesics, correct coagulopathy.
      • Intervention if necessary: Angiographic embolization or surgical evacuation.

Malignant Neoplasms of the Abdominal Wall

  • Desmoid Tumor (Fibromatosis):
    • Definition: Locally aggressive mesenchymal tumor without metastatic potential.
    • Epidemiology:
      • Incidence: 2–4 cases per million per year.
      • Occurs in young/middle-aged adults; female predominance.
      • 10–15% associated with FAP, Gardner, or Turcot syndromes.
    • Pathogenesis:
      • Sporadic Cases: Mutations in CTNNB1 gene, leading to β-catenin accumulation.
      • FAP-Associated: Mutations in APC gene.
    • Presentation:
      • Firm, nonpainful mass in the abdominal wall or other locations.
      • Infiltrative growth pattern.
    • Diagnosis:
      • MRI is preferred imaging.
      • Core needle biopsy for histology.
    • Management:
      • Watchful Waiting:
        • Close monitoring due to potential spontaneous regression.
      • Surgical Resection:
        • For symptomatic or progressing tumors.
      • Radiation Therapy:
        • Limited use due to risks.
      • Systemic Therapy:
        • Antihormonal agents (tamoxifen), NSAIDs.
        • Chemotherapy for aggressive cases.
        • Tyrosine kinase inhibitors (imatinib, sorafenib).
  • Abdominal Wall Sarcoma:
    • Definition: Malignant tumors of mesenchymal origin affecting the abdominal wall (<5% of sarcomas).
    • Common Types:
      • Liposarcoma, myxofibrosarcoma, leiomyosarcoma, rhabdomyosarcoma, undifferentiated pleomorphic sarcoma.
    • Presentation:
      • Firm, painless mass fixed to muscle and fascia.
    • Risk Factors:
      • Radiation exposure, genetic syndromes (neurofibromatosis, Li-Fraumeni).
    • Diagnosis:
      • Imaging with CT/MRI.
      • Core needle biopsy.
    • Treatment:
      • Surgical resection with negative margins (≥2 cm).
      • May require reconstructive surgery.
      • Radiation therapy for certain cases.
    • Prognosis:
      • Dependent on grade, stage, and resection margins.
      • Local recurrence rate: 10–15% after negative margins.
  • Metastatic Disease:
    • Definition: Abdominal wall involvement from advanced malignancies.
    • Sources:
      • Hematogenous spread (lung, colon, renal carcinoma, melanoma).
      • Tumor implantation during procedures.
    • Presentation:
      • Firm abdominal wall mass.
    • Diagnosis:
      • Imaging and core needle biopsy.
    • Management:
      • Palliative care focusing on symptom relief.
      • Systemic therapy for disseminated disease.
      • Radiation or surgery for symptomatic lesions.

Symptoms of Intraabdominal Disease Referred to the Abdominal Wall

  • Types of Abdominal Pain:
    • Visceral Pain:
      • Caused by inflammation, distention, or ischemia of internal organs.
      • Dull, poorly localized, often midline.
      • Accompanied by autonomic symptoms (nausea, vomiting).
    • Somatoparietal Pain:
      • Originates from the parietal peritoneum.
      • Sharp, well-localized, may lateralize.
      • Transmitted via somatic nerves.
    • Referred Pain:
      • Pain perceived at a location distant from the source due to shared neural pathways.
      • Examples:
        • Shoulder pain from diaphragmatic irritation.
        • Scapular pain from biliary disease.
        • Testicular or labial pain from retroperitoneal inflammation.
  • Example - Acute Appendicitis:
    • Early: Visceral pain felt as vague periumbilical discomfort.
    • Later: Somatoparietal pain localized at McBurney point in the right lower quadrant.
  • Mechanism of Referred Pain:
    • Convergence of visceral and somatic afferent neurons in the spinal cord leading to misinterpretation of pain origin.

PERITONEUM AND PERITONEAL CAVITY

Anatomy

  • Peritoneum:
    • A single layer of simple squamous epithelium (mesothelium) on a connective tissue stroma.
    • Surface Area: Approximately 1.0 to 1.7 m², similar to total body surface area.
    • In males, the cavity is sealed; in females, it opens to the exterior via the fallopian tubes.
  • Components:
    • Parietal Peritoneum: Lines the abdominal walls and diaphragm.
    • Visceral Peritoneum: Covers the surfaces of intraperitoneal organs.
  • Peritoneal Ligaments and Mesenteries:
    • Include the coronary, gastrohepatic, hepatoduodenal, falciform, gastrocolic, duodenocolic, gastrosplenic, splenorenal, phrenicocolic ligaments, and the transverse mesocolon and small bowel mesentery.
    • Function: Subdivide the peritoneal cavity into nine potential spaces, influencing fluid circulation and spread of disease.
  • Peritoneal Spaces:
    • Right and Left Subphrenic
    • Subhepatic
    • Supramesenteric and Inframesenteric
    • Right and Left Paracolic Gutters
    • Pelvis
    • Lesser Space
  • Blood Supply:
    • Visceral Peritoneum: Supplied by splanchnic vessels.
    • Parietal Peritoneum: Supplied by branches of the intercostal, subcostal, lumbar, and iliac vessels.

Physiology

  • Functions:
    • Acts as a bidirectional, semipermeable membrane.
    • Controls fluid amount in the peritoneal cavity.
    • Removes bacteria and facilitates immune responses.
  • Peritoneal Fluid:
    • Normally contains <100 mL of sterile serous fluid.
    • Microvilli increase surface area for rapid absorption.
  • Fluid Circulation:
    • Driven by diaphragmatic movement.
    • Stomata in the diaphragm communicate with lymphatics.
    • Diaphragmatic Pump:
      • Exhalation: Relaxation opens stomata, drawing fluid in.
      • Inhalation: Contraction propels lymph into thoracic duct.
  • Response to Infection:
    1. Rapid bacterial removal via lymphatics.
    2. Inflammatory mediators released by macrophages.
    3. Mast cell degranulation releases histamine, increasing permeability.
    4. Protein-rich fluid opsonizes bacteria, enhancing phagocytosis.
    5. Fibrin matrices form, leading to abscess formation and limiting spread.

Peritoneal Disorders

Ascites

  • Definition: Pathological accumulation of fluid in the peritoneal cavity.

  • Causes:

    • Cirrhosis (most common, ~85% of cases).
    • Portal hypertension, heart failure, nephrotic syndrome, malignancies, pancreatic, bile, or lymphatic leakage.

    image.png

  • Pathophysiology in Cirrhosis:

    • Renal Sodium and Water Retention:
      • Activation of renin-angiotensin-aldosterone and sympathetic nervous systems.
    • Portal Hypertension:
      • Increased hydrostatic pressure due to postsinusoidal obstruction.
    • Splanchnic Vasodilation:
      • Nitric oxide release decreases effective circulating volume.
  • Clinical Presentation:
    • Abdominal distention, dullness on percussion.
    • Signs of cirrhosis: Palmar erythema, spider angiomas.
    • Jugular venous distention in cardiac ascites.

  • Diagnosis:

    • Paracentesis with fluid analysis.

    • Serum-Ascites Albumin Gradient (SAAG):

      • ≥1.1 g/dL: Indicates portal hypertension.
      • <1.1 g/dL: Suggests other causes.

      image.png

  • Ascitic Fluid Analysis:

    • Appearance:
      • Clear/yellow: Normal.
      • Cloudy: High leukocyte count.
      • Blood-tinged: Traumatic tap or hemoperitoneum.
      • Milky: Chylous ascites.
    • Cell Count and Differential:
      • PMNs >250 cells/mm³: Suggests infection.
  • Treatment in Cirrhosis:
    • Sodium Restriction: 2 g/day.
    • Diuretics:
      • Spironolactone and furosemide in a 100:40 mg ratio.
    • Large-Volume Paracentesis:
      • For refractory ascites.
      • Albumin infusion (6–8 g/L of fluid removed) to prevent complications.
    • Advanced Interventions:
      • Transjugular Intrahepatic Portosystemic Shunt (TIPS).
      • Liver transplantation for refractory cases.

Chylous Ascites

  • Definition: Accumulation of chyle (lymphatic fluid rich in triglycerides) in the peritoneal cavity.
  • Mechanisms:
    1. Lymphatic Obstruction at mesenteric base or cisterna chyli.
    2. Lymphoperitoneal Fistula from abnormal or injured lymphatics.
    3. Exudation from Megalymphatics without visible fistula.
  • Common Causes:
    • Adults: Intraabdominal malignancies (especially lymphoma).
    • Children: Trauma, congenital lymphatic abnormalities.
  • Clinical Presentation:
    • Painless abdominal distention.
    • Malnutrition, dyspnea.
  • Diagnosis:
    • Milky ascitic fluid.
    • High triglyceride levels (2–8 times plasma levels).
    • SAAG <1.1 g/dL.
  • Management:
    • Nutritional Support:
      • High-protein, low-fat diet with medium-chain triglycerides.
    • Diuretics.
    • Paracentesis for symptom relief.
    • Surgical Exploration if conservative measures fail.

Peritonitis

  • Definition: Inflammation of the peritoneum, often due to infection.
  • Types:
    • Primary Peritonitis: Infection without a perforated viscus.
    • Secondary Peritonitis: Resulting from GI or GU tract perforation or inflammation.

Spontaneous Bacterial Peritonitis (SBP)

  • Definition: Infection of ascitic fluid without an evident intraabdominal source.
  • Associated Conditions:
    • Cirrhosis, nephrotic syndrome, heart failure.
  • Common Pathogens:
    • Adults: Escherichia coli, Klebsiella pneumoniae.
    • Children: Group A Streptococcus, Staphylococcus aureus, Streptococcus pneumoniae.
  • Pathogenesis:
    • Bacterial Translocation from the gut due to impaired immunity and motility.
    • Low ascitic fluid protein impairs bacterial opsonization.
  • Diagnosis:
    • Ascitic fluid PMNs >250 cells/mm³.
    • Monomicrobial cultures.
    • Clinical symptoms: Abdominal pain, fever, leukocytosis.
  • Treatment:
    • Immediate broad-spectrum antibiotics: Third-generation cephalosporins.
    • Albumin infusion to reduce risk of renal failure.
  • Prognosis:
    • Immediate mortality is low with prompt treatment.
    • Long-term prognosis is poor due to associated complications.

Tuberculous Peritonitis

  • Cause: Reactivation of latent Mycobacterium tuberculosis infection in the peritoneum.
  • Risk Factors:
    • Immunodeficiency (e.g., HIV), cirrhosis, chronic renal failure.
  • Clinical Presentation:
    • Abdominal swelling due to ascites.
    • Vague abdominal pain.
    • Constitutional symptoms: Low-grade fever, night sweats, weight loss.
  • Diagnosis:
    • Positive tuberculin skin test.
    • Ascitic fluid analysis:
      • SAAG <1.1 g/dL.
      • High lymphocyte count.
      • Elevated adenosine deaminase activity.
    • Imaging: Ultrasound or CT may show characteristic findings.
    • Definitive Diagnosis:
      • Laparoscopy with peritoneal biopsy showing caseating granulomas.
  • Treatment:
    • Antituberculous therapy: Typically isoniazid and rifampin for 9 months.

Peritonitis Associated with CAPD

  • Incidence: One episode every 1 to 3 years in patients on chronic ambulatory peritoneal dialysis (CAPD).
  • Common Pathogens:
    • Gram-positive bacteria (75%), especially Staphylococcus epidermidis.
    • Gram-negative bacilli and fungi are less common.
  • Clinical Presentation:
    • Abdominal pain, fever.
    • Cloudy peritoneal dialysate with >100 leukocytes/mm³.
  • Treatment:
    • Intraperitoneal antibiotics: Often a first-generation cephalosporin.
    • Catheter removal if infection is refractory or recurrent.
  • Complications:
    • Major cause of technical failure in CAPD.

Malignant Neoplasms of the Peritoneum

  • Common Sources:
    • Peritoneal carcinomatosis from GI (stomach, colon, pancreas) and GU (ovarian) cancers.
  • Primary Peritoneal Malignancies:
    • Pseudomyxoma peritonei
    • Peritoneal mesothelioma
    • Primary peritoneal carcinoma

Pseudomyxoma Peritonei

  • Definition: Accumulation of mucinous ascites and peritoneal implants, typically from a perforated appendiceal mucinous tumor.
  • Pathology:
    • Mucus and cells distribute throughout the peritoneal cavity.
    • Low-grade (adenomucinosis) vs. high-grade (peritoneal mucinous carcinomatosis).
  • Clinical Presentation:
    • Abdominal distention, pain.
    • Possible new hernia, ascites, or palpable mass.
  • Diagnosis:
    • CT Imaging: Shows ascites, peritoneal implants, omental thickening.
    • Colonoscopy: To exclude colonic origin.
    • Intraoperative discovery: Tenacious mucus and cystic masses.
  • Treatment:
    • Cytoreductive Surgery:
      • Removal of tumor, omentectomy, peritoneal stripping.
    • Hyperthermic Intraperitoneal Chemotherapy (HIPEC):
      • Administered intraoperatively using agents like mitomycin C or oxaliplatin.
  • Prognosis:
    • Low-grade tumors: 5-year survival of 60–90% with complete cytoreduction and HIPEC.
    • High-grade tumors: 5-year survival ~50% if complete cytoreduction is achieved.
  • Complications:
    • Postoperative morbidity: Prolonged ileus, pulmonary complications, infections.

Carcinomatosis from Colorectal Cancer

  • Incidence: Occurs in ~8% of colorectal cancer patients.
  • Treatment:
    • Cytoreductive Surgery with HIPEC:
      • Shows improved survival in selected patients with limited peritoneal disease.
      • Recent studies suggest similar outcomes with cytoreduction alone.

Peritoneal Mesothelioma

  • Definition: A rare malignant tumor arising from the peritoneal mesothelium.
  • Epidemiology:
    • ~800 cases per year in the U.S.
    • Affects men and women equally.
    • Median age at presentation: 50 years.
    • Asbestos exposure in ~33% of cases.
  • Histological Subtypes:
    • Epithelioid (most common, best prognosis).
    • Sarcomatoid.
    • Biphasic.
  • Clinical Presentation:
    • Abdominal pain, weight loss, ascites.
    • Possible omental mass.
  • Diagnosis:
    • CT Imaging: Shows mesenteric thickening, peritoneal nodules.
    • Biopsy:
      • Often requires laparoscopy for tissue diagnosis.
  • Treatment:
    • Cytoreductive Surgery with HIPEC:
      • Achieves median survival of 30–60 months.
      • Complete cytoreduction is key for better outcomes.
    • Systemic Chemotherapy:
      • Agents like cisplatin and pemetrexed for nonsurgical candidates.
  • Prognosis:
    • 5-year survival ~42% with complete cytoreduction and HIPEC.
    • Epithelioid subtype has a better prognosis.
  • Complications:
    • Similar to those associated with HIPEC in other peritoneal malignancies.

MESENTERY AND OMENTUM

Embryology and Anatomy

  • Greater and Lesser Omenta:
    • Greater Omentum: Extends from the greater curvature of the stomach over the small intestine; formed from the dorsal mesogastrium.
    • Lesser Omentum: Connects the lesser curvature of the stomach and proximal duodenum to the liver; derived from the ventral mesentery.
  • Embryonic Development:
    • Stomach Rotation:
      • Rotates 90 degrees on its longitudinal axis.
      • Lesser curvature faces right; greater curvature faces left.
    • Ventral Mesentery:
      • Mostly resorbed during development.
      • Gastrohepatic ligament persists as part of the lesser omentum.
      • Foramen of Winslow: Opening into the lesser sac; bordered by the free edge of the lesser omentum.
    • Dorsal Mesogastrium:
      • Forms the greater omentum.
      • Extends from the stomach over the small intestine and up to the transverse colon.
      • Accumulates fat to form the omental apron.
  • Mesentery:
    • Supports the jejunum and ileum.
    • Contains mesenteric blood vessels and lymphatics.
    • Attaches obliquely from the duodenojejunal junction to the right iliac fossa.

Physiology

  • Omentum and Mesentery:
    • Rich in lymphatics and blood vessels.
    • Contains macrophages aiding in removal of bacteria and foreign material.
    • Omental Adherence:
      • Becomes adherent to sites of inflammation.
      • Prevents diffuse peritonitis in cases like appendicitis or diverticulitis.

Diseases of the Omentum

Omental Cysts

  • Definition: Unilocular or multilocular cysts containing serous fluid, arising from obstruction of omental lymphatic channels.
  • Etiology: Similar to cystic lymphangiomas; lined by lymphatic endothelium.
  • Epidemiology:
    • Most common in children and young adults.
    • Small cysts: Usually asymptomatic, found incidentally.
    • Large cysts: May present as a palpable abdominal mass.
  • Clinical Features:
    • Location: Typically in the lower mid-abdomen.
    • Characteristics: Freely movable, smooth, nontender.
    • Complications (more common in children): Torsion, infection, rupture.
  • Diagnosis:
    • Imaging:
      • Plain radiographs: Soft tissue density.
      • Contrast studies: Displacement of intestinal loops.
      • Ultrasound/CT: Fluid-filled cystic mass with internal septations.
    • Differential Diagnosis: Includes cysts/tumors of mesentery, peritoneum, retroperitoneum, desmoid tumors.
  • Treatment:
    • Local excision (laparoscopic or open) is curative.
    • Histologic examination of the cyst wall is essential.

Omental Torsion and Infarction

  • Definition: Axial twisting of the greater omentum along its long axis, potentially leading to infarction and necrosis.
  • Classification:
    • Primary Torsion: No associated condition.
    • Secondary Torsion: Associated with hernia, tumor, or adhesion.
  • Epidemiology:
    • Occurs twice as often in men.
    • Most frequent in the 4th or 5th decade of life.
    • Primary torsion usually involves the right side.
  • Clinical Presentation:
    • Acute onset of severe right-sided abdominal pain.
    • Nausea and vomiting: May be present but not predominant.
    • Normal temperature.
    • Physical Exam:
      • Localized tenderness with guarding.
      • Possible palpable abdominal mass.
  • Differential Diagnosis:
    • Acute appendicitis.
    • Acute cholecystitis.
    • Ovarian cyst torsion.
  • Diagnosis:
    • CT Scan: Shows an omental mass with signs of inflammation.
  • Treatment:
    • Surgical intervention (laparotomy or laparoscopy).
    • Resection of the involved omentum.
    • Address any related conditions.

Omental Neoplasms

  • Primary Malignant Neoplasms:
    • Extremely rare.
    • Usually sarcomas (soft tissue origin).
  • Secondary Involvement:
    • Omentum commonly involved by metastatic tumors.
    • Spread transperitoneally from intraabdominal or pelvic malignancies.

Omental Grafts and Transpositions

  • Vascular Supply:
    • Derived from the right and left gastroepiploic arteries.
  • Applications:
    • Omental Pedicle Flap:
      • Created by mobilizing the omentum and dividing vessels.
      • Used to cover chest and mediastinal wounds.
      • Prevents small intestine from entering the pelvis post-abdominoperineal resection.
    • Graham Patch:
      • Omentum used to patch duodenal perforations from peptic ulcer disease.
      • Forms dense adhesions to sites of perforation or inflammation.

Diseases of the Mesentery

Mesenteric Cysts

  • Definition: Non-neoplastic mesothelial cysts containing chyle or clear serous fluid.
  • Location:
    • Small intestine mesentery (60%).
    • Colon mesentery (40%).
  • Epidemiology:
    • Mean age: 45 years.
    • Twice as common in women.
  • Clinical Features:
    • Symptoms depend on cyst size:
      • Abdominal pain.
      • Fever.
      • Emesis.
    • Physical Exam: Palpable midabdominal mass.
  • Diagnosis:
    • Ultrasound or CT scan preoperatively.
  • Treatment:
    • Enucleation of the cyst at laparotomy is curative.
    • Internal drainage for very large cysts.
    • Aspiration alone is discouraged due to high recurrence.
    • Histologic examination to rule out neoplasm if cyst not fully excised.

Acute Mesenteric Lymphadenitis

  • Definition: Syndrome of acute right lower quadrant pain with mesenteric lymph node enlargement and a normal appendix.
  • Epidemiology:
    • Most common in children and young adults.
    • Affects males and females equally.
  • Etiology:
    • Caused by viral, bacterial, parasitic, or fungal infections.
    • Yersinia enterocolitica is a notable cause in children.
  • Clinical Presentation:
    • Acute periumbilical pain shifting to the right lower quadrant.
    • Tenderness, muscle rigidity, and rebound tenderness.
    • Nausea, vomiting, diarrhea, anorexia.
    • Fever and elevated white blood cell count.
  • Diagnosis:
    • Abdominal ultrasound is recommended for definitive diagnosis.
    • Differentiates from acute appendicitis.
  • Management:
    • Conservative treatment as the condition is self-limiting.
    • Avoid unnecessary surgery.

Sclerosing Mesenteritis

  • Definition: Rare inflammatory disease characterized by sclerosing fibrosis, fat necrosis, and chronic inflammation of the mesentery.
  • Pathology:
    • Histology:
      • Sclerosing fibrosis.
      • Fat necrosis with lipid-laden macrophages.
      • Chronic inflammation with germinal centers.
      • Focal calcification.
    • Gross Appearance:
      • Thickened mesentery with areas of fat necrosis.
      • May present as multiple nodules or a single mass.
      • Often involves the root of the small bowel mesentery.
  • Epidemiology:
    • Twice as common in men.
    • Occurs typically in the 5th decade of life.
  • Clinical Features:
    • Many patients are asymptomatic.
    • When symptomatic:
      • Abdominal pain.
      • Symptoms of intestinal obstruction: Nausea, vomiting, distention.
      • Palpable abdominal mass in >50% of cases.
    • Laboratory Tests: May show elevated ESR and C-reactive protein.
  • Diagnosis:
    • CT Imaging characteristics:
      • Fatty mass with pseudocapsule.
      • Fat ring sign: Normal adipose around mesenteric vessels.
      • Normal vessels coursing through the mass without involvement.
      • Mass displacing but not invading bowel loops.
    • Definitive Diagnosis: Biopsy via laparoscopy or laparotomy.
  • Management:
    • Many cases resolve spontaneously.
    • Corticosteroids and immunosuppressive agents may be used if symptoms persist.
    • Surgery only if diagnosis is uncertain or to relieve obstruction.

Intraabdominal (Internal) Hernias

Internal Hernias Caused by Developmental Defects

  • Mechanisms:
    1. Abnormal mesenteric fixation (e.g., mesocolic hernia).
    2. Enlarged internal foramina (e.g., foramen of Winslow hernia).
    3. Incomplete mesenteric surfaces allowing herniation (e.g., mesenteric hernia).

Mesocolic (Paraduodenal) Hernias

  • Definition: Herniation of small intestine behind the mesocolon due to abnormal midgut rotation.

  • Types:

    • Right Mesocolic Hernia:
      • Failure of prearterial midgut loop rotation.
      • Small intestine remains on the right of the superior mesenteric artery (SMA).

    • Left Mesocolic Hernia:

      • Herniation between the inferior mesenteric vein (IMV) and the posterior parietal peritoneum.
      • Occurs on the left side (75% of cases).

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  • Clinical Presentation:

    • Symptoms of acute or chronic small bowel obstruction.
  • Diagnosis:
    • Barium radiographs: Displacement of small intestine.
    • CT scan: Displacement of mesenteric vessels, signs of obstruction.
  • Treatment:
    • Right Mesocolic Hernia:
      • Incise lateral peritoneal reflections along the right colon.
      • Reflect right colon and cecum to the left.
    • Left Mesocolic Hernia:
      • Incise peritoneal attachments along the right side of the IMV.
      • Reduce herniated intestine from beneath the IMV.
      • Close hernia neck by suturing peritoneum to retroperitoneum.

Mesenteric Hernias

  • Definition: Herniation of intestine through an abnormal mesenteric orifice.
  • Common Location: Near the ileocolic junction.
  • Clinical Presentation:
    • Intestinal obstruction due to compression or torsion.
  • Treatment:
    • Reduction of herniated intestine.
    • Closure of the mesenteric defect.

Acquired Internal Hernias

  • Cause: Postoperative or traumatic creation of mesenteric defects.
  • Common After:
    • Procedures like gastrojejunostomy, colostomy, ileostomy, bowel resection.
  • Risk Variation:
    • Low risk after laparoscopic colectomy (~1%); defect often not closed.
    • Higher risk after laparoscopic Roux-en-Y gastric bypass (~9%); defect usually closed.
  • Treatment:
    • Operative reduction of hernia.
    • Closure of peritoneal defect.

Malignant Neoplasms of the Mesentery

Mesenteric and Intraabdominal Desmoid Tumors

  • Definition: Primary malignant tumors of the mesentery; a type of desmoid tumor.
  • Association with FAP:
    • 80% of desmoid tumors in FAP patients are intraabdominal.
    • Particularly common in Gardner syndrome.
  • Risk Factors:
    • Surgical procedures can induce or progress desmoid tumors.
    • Lower risk with laparoscopic proctocolectomy compared to open surgery.
  • Clinical Features:
    • May cause bowel obstruction, ischemia, hydronephrosis, vascular involvement.
  • Treatment Challenges:
    • Complete resection is often difficult due to critical structures.
    • Resection may require sacrificing significant lengths of intestine.
  • Management Strategy:
    • Watchful waiting for stable tumors due to variable behavior.
    • Systemic therapy:
      • Antiestrogens and NSAIDs for slow-growing tumors.
      • Cytotoxic chemotherapy for aggressive tumors.
  • Prognosis:
    • 10-year survival rate: 60–70%.

RETROPERITONEUM

Anatomy

  • Location:
    • Space between the peritoneum and posterior parietal wall of the abdominal cavity.
    • Extends from the diaphragm to the pelvis.
  • Subdivisions:
    • Lumbar Fossa:
      • Superiorly: 12th thoracic vertebra, lateral lumbocostal arch.
      • Inferiorly: Sacrum base, iliac crest, iliolumbar ligament.
      • Floor: Fascia over quadratus lumborum and psoas major muscles.
      • Contains: Adrenal glands, kidneys, ascending and descending colon, pancreas, duodenum, ureter, renal vessels, gonadal vessels, inferior vena cava, aorta.
    • Iliac Fossa:
      • Contiguous with lumbar fossa superiorly.
      • Floor: Iliacus muscle with investing fascia.
      • Contains: Iliac vessels, ureter, genitofemoral nerve, gonadal vessels, iliac lymph nodes.

Operative Approaches

  • Retroperitoneal Access:
    • Used for procedures on aorta, vena cava, iliac vessels, kidneys, adrenal glands.
    • Common surgeries: Adrenalectomy, nephrectomy, renal transplantation.
  • Advantages over Transabdominal Approach:
    • Less postoperative ileus.
    • Faster resumption of diet and earlier discharge.
    • No intraabdominal adhesions, reducing risk of small bowel obstruction.
    • Less intraoperative fluid loss and fewer fluid shifts.
    • Reduced respiratory complications (e.g., atelectasis, pneumonia).

Retroperitoneal Disorders

Retroperitoneal Abscesses

  • Classification:
    • Primary: From hematogenous spread.
    • Secondary: Related to infection in an adjacent organ.
  • Causes (Box 44.2):
    • Renal diseases: Pyelonephritis.
    • GI diseases: Diverticulitis, appendicitis, Crohn disease.
    • Hematogenous spread from remote infections.
    • Postoperative complications.
    • Bone infections: Tuberculosis of the spine.
    • Trauma, malignant neoplasms, miscellaneous causes.
  • Common Pathogens:
    • Renal origin: E. coli, Proteus mirabilis (monomicrobial).
    • GI origin: E. coli, Enterobacter spp., enterococci, Bacteroides (polymicrobial).
    • Hematogenous spread: Staphylococcal species (monomicrobial).
    • Tuberculosis: Mycobacterium tuberculosis (common in immunocompromised patients).
  • Clinical Presentation:
    • Abdominal or flank pain (60–75%).
    • Fever and chills (30–90%).
    • Malaise, weight loss.
    • Psoas abscess: Pain referred to hip, groin, or knee.
    • Often associated with chronic illnesses: Renal stones, diabetes, HIV, malignancies.
  • Diagnosis:
    • CT scan: Low-density mass with surrounding inflammation; gas in up to one third of cases.
    • Helps identify location and source of infection.
  • Treatment:
    • Antibiotics appropriate to causative organisms.
    • Drainage:
      • CT-guided percutaneous drainage is effective.
      • Surgical drainage via retroperitoneal approach if percutaneous drainage fails or is not feasible.
    • Prognosis depends on underlying comorbidities.

Retroperitoneal Hematomas

  • Causes:
    • Blunt or penetrating trauma.
    • Ruptured aneurysms: Abdominal aortic or visceral artery.
    • Anticoagulation therapy complications.
    • Fibrinolytic therapy.
    • Bleeding disorders: Hemophilia.
  • Clinical Presentation:
    • Abdominal or flank pain radiating to groin, labia, or scrotum.
    • Signs of acute blood loss: Hypotension, tachycardia.
    • Abdominal mass, ileus.
    • Femoral neuropathy in 20–30% of patients.
    • Laboratory findings: Anemia, coagulopathy, microscopic hematuria.
  • Diagnosis:
    • CT scan: High-density mass in retroperitoneum with tissue plane stranding.
    • Differentiated from abscesses by density on imaging.
  • Management:
    • Resuscitation: Restore blood volume.
    • Correct coagulopathy.
    • Intervention:
      • Angiography with embolization for active bleeding.
      • Surgical exploration rarely required.

Retroperitoneal Fibrosis

  • Definition: Chronic inflammation and fibrosis in the retroperitoneum, often encasing the aorta, iliac arteries, and ureters.
  • Etiology:
    • Idiopathic (Ormond disease): ~70%.
    • Secondary: Drugs (e.g., ergot alkaloids), infections, trauma, hemorrhage, surgery, radiation, neoplasms.
    • Associated with inflammatory abdominal aortic aneurysms.
  • Pathogenesis:
    • May be a manifestation of systemic autoimmune disease.
    • Linked to HLA-DRB1*03 allele.
    • Histologic similarities to vasculitides.
  • Epidemiology:
    • Male predominance (2–3:1).
    • Mean age: 50–60 years.
  • Clinical Presentation:
    • Localized pain: Side, back, abdomen.
    • Lower extremity edema.
    • Scrotal swelling, varicocele, hydrocele.
    • Constitutional symptoms: Fatigue, low-grade fever, weight loss, myalgias.
    • Laboratory findings: Elevated ESR, C-reactive protein, possible azotemia.
    • Ureteral involvement: Present in 80–100% of cases.
  • Diagnosis:
    • Imaging:
      • CT scan: Homogeneous fibrous plaque around aorta and iliac arteries.
      • MRI:
        • Early disease: High signal on T2-weighted images.
        • Mature fibrosis: Low signal on T1- and T2-weighted images.
  • Treatment Goals:
    • Halt progression of fibrosis.
    • Relieve ureteral obstruction.
    • Suppress systemic inflammation.
    • Improve symptoms.
  • Management:
    • Medical Therapy:
      • Corticosteroids: First-line treatment.
      • Immunosuppressants: For steroid-resistant cases (e.g., mycophenolate mofetil, cyclophosphamide, azathioprine, methotrexate, tamoxifen).
    • Ureteral Stenting: Temporary relief of obstruction.
    • Surgical Intervention:
      • Ureterolysis with intraperitoneal transposition and omental wrapping.
      • Reserved for refractory cases.
  • Association with Aneurysms:
    • Repair abdominal aortic aneurysm if diameter >4.5–5 cm.
    • Impact of aneurysm repair on fibrosis progression is variable.

Retroperitoneal Malignant Neoplasms

  • Types:
    • Primary:
      • Sarcomas (most common): Liposarcoma, leiomyosarcoma.
      • Lymphoma.
      • Extragonadal germ cell tumors.
    • Secondary:
      • Extension from retroperitoneal organs: Kidney, adrenal, colon, pancreas.
      • Metastases: GU lymph node metastases.

Retroperitoneal Sarcoma

  • Epidemiology:
    • 15% of soft tissue sarcomas arise in the retroperitoneum.
  • Histologic Subtypes:
    • Liposarcoma.
    • Leiomyosarcoma.
  • Clinical Presentation:
    • Large abdominal mass.
    • Abdominal pain (~50%).
    • Symptoms from organ compression:
      • Early satiety, nausea, vomiting.
      • Constipation, weight loss.
      • Lower extremity edema.
    • Neurologic symptoms: Paresthesia, paresis due to nerve compression.

  • Diagnosis:

    • CT or MRI:
      • Determines size, location, relation to vessels.
      • Identifies metastatic disease.
      • Liposarcomas: Variable fat density.

    • Differential Diagnosis:

      • Lymphoma, testicular cancer (check alpha-fetoprotein, hCG).
      • Extension of cancers from adrenal, renal, pancreatic origins.

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  • Treatment:

    • Surgical Resection:
      • Goal: Complete resection with negative margins (R0).
      • En bloc resection of involved organs.
      • Lymphadenectomy not routinely required.
      • Complex surgeries best performed at specialized centers.
    • Incomplete Resection (R2):
      • Similar survival to unresectable cases.
      • May be considered for palliative purposes or for well-differentiated liposarcomas.
  • Prognosis:
    • Complete resection achieved in 50–67% of cases.
    • Local recurrence in 25–50% after resection.
    • Repeat resection beneficial for isolated local recurrence.
  • Adjuvant Therapy:
    • Radiation Therapy:
      • Limited use due to toxicity to adjacent organs.
      • Lack of prospective trials showing survival benefit.
      • Preoperative radiation may reduce toxicity and improve targeting.
      • Ongoing trials assessing its efficacy.

This structured summary emphasizes essential information on the retroperitoneum, its anatomy, disorders, and particularly retroperitoneal sarcoma, providing a concise review suitable for last-minute exam preparation.