Disorders of the Small and Large Bowel

Disorders of the Small and Large Bowel

• The small intestine measures approximately 6 meters in length.
• The first 25 cm of the small intestine, the duodenum, is retroperitoneal.
• The first one-third of the intraperitoneal part of the small intestine is the jejunum.
• The remainder of the small intestine is the ileum.
• The arterial supply to the small intestine is the superior mesenteric artery.

Disorders of the Small Bowel

Non-Neoplastic Disorders

• Congenital Anomalies

  • Heterotopic gastric mucosa
  • Heterotopic pancreas
  • Meckel's diverticulum
  • Malrotation, stenosis, atresia, duplication, and defects of musculature

• Malabsorptive disorders

  • Celiac disease
    • Characterized by malabsorption, abnormal small bowel structure, and intolerance to gluten.
    • Pathogenesis involves sensitivity to gluten protein components of wheat, oats, barley, and rye.
    • Immune-mediated response.
    • Associated with increased milk intolerance, diabetes, ulcerative colitis, and primary sclerosing cholangitis.
    • Morphology shows diffuse enteritis, atrophy/loss of villi, and increased intraepithelial lymphocytes
  • Tropical sprue
    • Celiac-like disease affecting people in tropical regions.
    • No specific causative agent identified but may involve E. coli and Hemophilus.
    • Pathology ranges from normal to diffuse enteritis
    • Malabsorption, but no risk of intestinal lymphoma.
    • Treated using antibiotics.
  • Whipple disease
    • Rare systemic disease, Hallmark is distended macrophages in the lamina propria of the small intestine (mostly jejunum).
    • Inflammation is absent at the site of infection.
    • Mostly affects males aged 30-40.
    • Often an atypical presentation, with >50% incidence of lymphadenopathy and skin hyperpigmentation.

• Infectious Diseases

  • Infectious enterocolitis
    • Common gastrointestinal viruses (Rota virus, Norwalk virus, enteric virus).
    • Bacterial pathogens (E. coli, Salmonella, Campylobacter, Vibrio cholera, Clostridium perfringens, Enteroinvasive E. coli, Shigella).
    • Post-infectious complications, like reactive arthritis, Guillain-Barré syndrome, immune-proliferative small intestinal disease, can occur with Campylobacter infection.
  • Parasitic diseases
    • Giardiasis does not cause villus architectural changes.
    • Diagnosis involves microscopic identification of pear-shaped trophozoites using trichrome/Giemsa stains.
    • Other parasitic diseases include Ascaris lumbricoides and Strongyloides.
  • Typhoid Fever (Salmonella typhi and paratyphi)
    • Acute infection, associated with bloody diarrhoea and flu-like symptoms.
    • Morphology shows enlarged Peyer's patches in the terminal ileum, with oval ulcers oriented along the ileum's long axis
    • Complications include bacteremia and extra-intestinal involvement.

• Crohn disease and acquired diverticula

• Polyps

Neoplasms

• Polyps
• WHO classification of tumors

Acquired Diverticula

• False diverticula
• Increase with age
• Most common site is the duodenum
• Pathophysiology involves bacterial overgrowth, leading to periampullary diverticula that cause obstructive jaundice and intestinal obstruction.

Polyps and Neoplasms

Benign Tumors

• Adenomas (commonest benign neoplasm)
  • True adenomas (ileum), are usually asymptomatic but may cause bleeding and obstruction.
  • Villous adenomas (duodenum), with no malignant potential.
• Brunner's gland adenoma (duodenum)
• Leiomyoma (most common symptomatic benign lesion, usually causing bleeding)
• Lipoma (most common in ileum, causes obstruction)
• Peutz-Jeghers polyps (autosomal dominant; multiple polyps in the GIT; jejunum/ileum are the frequent sites; mucocutaneous melanotic pigmentation but no malignant potential)

Malignant Tumors

• Adenocarcinoma of the small bowel
  • Rare (2% of primary GIT tumours)
  • Predominantly occurs in the duodenum.
• Carcinoid Tumour
  • Accounts for >50% of malignant tumours in the small intestine.
  • Arises from Enterochromaffin/Kulchitsky cells.
  • Malignant potential varies with the location (e.g., appendicular vs. ileal)
  • Possible metastasis (e.g., lymph nodes, liver).

Intestinal Obstructions

• Hernia
• Adhesions
• Intussusception
• Volvulus

Intussusception

• Definition: A portion of the bowel invaginates into an adjacent section
• Typically occurs in children under 5 due to lymphoid hyperplasia
• Older patients may have intra-luminal tumors
• Potential complications include ischemic necrosis.

Diverticulosis

• Characterized by the presence of small pouches in the intestinal wall