Pathology of Small Intestine

Pathology of the Small Intestine

Congenital Disorders

Meckel Diverticulum

  • Definition: A true diverticulum is a blind outpouching of the alimentary tract, including all three layers of the bowel wall.

  • Epidemiology: Occurs in about 2% of the population and is more common in males.

  • Location: Usually presents within 2 feet of the ileo-caecal valve; typically 2 inches long.

  • Clinical Features: More often asymptomatic; about 4% are symptomatic by age 2.

Duodenal Atresia

  • Condition where an orifice is abnormally closed or absent causing complete obstruction.

Stenosis

  • Abnormal narrowing of a passage, less common than atresia.

Omphalocele

  • Herniation of abdominal viscera into a ventral membranous sac, often requires surgical repair.

Gastroschisis

  • Ventral wall defect involving all layers of the abdominal wall, causing intestinal displacement.

Infective Diseases

Infective Enterocolitis

  • Common pathogens include viruses, bacteria (Salmonella, Typhoid), and parasites (Giardia).

Typhoid Fever

  • Caused by: Salmonella typhi and paratyphi.

  • Transmission: Person-to-person or via contaminated food/water; most common in endemic regions.

  • Symptoms: Febrile illness with abdominal pain, diarrhea, or constipation.

  • Findings: Enlarged Peyer’s patches, thrombocytopenia, and necrosis in lymphoid tissues.

Tuberculous Enterocolitis

  • Caused by Mycobacterium tuberculosis, can arise from drinking contaminated milk or swallowing sputum.

Giardiasis

  • Caused by Giardia lamblia, most common parasitic infection.

  • Spread via contaminated water, resistant to chlorine.

  • Clinical Features: Chronic diarrhea, malabsorption, nausea, steatorrhea, or constipation.

Vascular Diseases

Ischaemic Bowel Disease

  • Pathogenesis: Can be due to acute arterial obstruction, chronic hypoperfusion, or mesenteric venous thrombosis.

  • Symptoms include abdominal pain, bloody diarrhea, and vomiting.

  • Morphology includes patchy mucosal hemorrhage, mucosal necrosis, and transmural infarction.

Inflammatory Bowel Disease

Types

  • Crohn Disease: Affects any part of the GI tract; transmural inflammation and skip lesions.

  • Ulcerative Colitis: Inflammation limited to colon and rectum affecting mucosa and submucosa.

Pathogenesis

  • Characterized by inappropriate mucosal immune activation.

  • Genetic predisposition with involvement of NOD2 gene.

Clinical Features

  • Symptoms include diarrhea, abdominal pain, fever, and weight loss.

  • Extra-intestinal manifestations: arthritis, skin conditions, and hepatobiliary diseases.

Malabsorption Syndrome

Causes

  • Conditions include Coeliac sprue, tropical sprue, lactose deficiency, Whipple disease, and abetalipoproteinaemia.

Symptoms

  • Chronic diarrhea, abdominal pain, weight loss, steatorrhea, and deficiencies in fat-soluble vitamins.

Coeliac Disease

  • Immune-mediated enteropathy triggered by gluten; characterized by villous atrophy and increased intraepithelial lymphocytes.

  • Symptoms vary significantly, and a strict gluten-free diet is essential for management.

Intestinal Obstruction

  • Often results from hernias, adhesions, intussusception, or volvulus.

  • Clinical symptoms include abdominal pain, distension, vomiting, and inability to pass stool.

Neoplasms of the Small Intestine

Types

  • Common malignant types: Adenocarcinomas, lymphomas, Lieberkühn tumors.

  • Benign types include adenomas, lipomas, and hamartomatous lesions like Peutz-Jegher polyps.

Carcinoid Tumor

  • Neuroendocrine tumors that can cause carcinoid syndrome if certain hormones are secreted into circulation.

  • Presentation includes flushing, gastrointestinal hypermotility, and potential metastases.

References

  1. Robbins and Cotran, Pathologic Basis of Disease, 8th Edition

  2. www.webpath.med.utah.edu