Small Intestine Pathology

Congenital Anomalies - Quirks & Twists

⭐ Meckel's diverticulum, the most common GI congenital anomaly, typically presents with painless rectal bleeding in children due to ectopic gastric mucosa.

• Meckel's Diverticulum: True diverticulum (all gut layers).
  • 📌 Rule of 2s: 2% population, 2 feet from ileocecal valve, 2 inches long, 2% symptomatic, 2 common ectopic tissues (gastric, pancreatic).
  • Complications: Bleeding (commonest), intussusception (lead point), diverticulitis, volvulus, perforation.
• Malrotation & Volvulus:
  • Abnormal midgut rotation; Ladd's bands may cause duodenal obstruction.
  • Midgut volvulus: Neonatal bilious emesis. Surgical emergency!
• Intestinal Atresia/Stenosis:
  • Duodenal: "Double bubble" sign on X-ray; strong association with Trisomy 21.
  • Jejunoileal: Caused by in-utero vascular accidents (e.g., SMA branch occlusion). "Apple peel" or "Christmas tree" deformity.

Inflammatory Conditions - Battles & Bugs

• Crohn's Disease (CD)
  • Skip lesions, cobblestone mucosa, string sign (barium)
  • Complications: fistulas, strictures, abscesses
  • ASCA positive
  • EIMs: arthritis, uveitis, erythema nodosum

  ⭐ Crohn's disease is characterized by transmural inflammation, non-caseating granulomas, and can affect any part of the GIT from mouth to anus, most commonly the terminal ileum.

• Intestinal Tuberculosis (TB)
  • Ileocecal commonest; transverse ulcers
  • Caseating granulomas
  • Complications: strictures, obstruction, perforation
  • 
• Typhoid (Enteric) Fever
  • Salmonella typhi; Peyer's patch hypertrophy (terminal ileum)
  • Longitudinal ulcers
  • Complications: perforation, hemorrhage (2nd-3rd week)
• Other Infections
  • Yersiniosis: mimics appendicitis, terminal ileitis
  • Whipple's Disease: T. whipplei; PAS+ macrophages, malabsorption, steatorrhea

Obstruction & Vascular Issues - Blockades & Bummers

• Small Bowel Obstruction (SBO)
  • Etiology: Adhesions (most common), hernias, tumors. 📌 "ABC": Adhesions, Bulges (hernias), Cancer.
  • Clinical (4 cardinal signs): Colicky pain, vomiting (bilious→faeculent), distension, obstipation.
  • Diagnosis: X-ray (dilated loops >3cm, air-fluid levels). CT confirms, shows cause/complications.
  • Management: NPO, IV fluids, NG tube. Surgery for strangulation, closed-loop, or no resolution.

  ⭐ Adhesions from previous surgery are the leading cause of small bowel obstruction in adults, while hernias are the second most common.

• Acute Mesenteric Ischemia (AMI)
  • Types: Arterial (embolus/thrombus), venous, NOMI.
  • Classic: Severe pain "out of proportion" to exam. ↑Lactate, metabolic acidosis.
  • Diagnosis: CT Angiography (CTA) is key.
  • Treatment: Urgent surgery (revascularization/resection of non-viable bowel). High mortality.

Small Bowel Neoplasms & SBS - Tumors & Takeouts

• Neoplasms: Often vague symptoms (pain, bleeding, obstruction).
  • Benign: Adenoma, Leiomyoma, Lipoma.
  • Malignant: AdenoCa (MC, duod/jej), Carcinoid (ileum), Lymphoma (ileum, celiac assoc.), GIST (c-KIT+).

  ⭐ Carcinoid tumors are the most common endocrine tumors of the GI tract, often arising in the ileum and appendix; hepatic metastases are required for carcinoid syndrome.

  • Carcinoid Syndrome (if liver mets): Flushing, diarrhea, bronchospasm. Dx: ↑ 5-HIAA.
• Short Bowel Syndrome (SBS):
  • Malabsorption if < 200 cm SB remaining.
  • Etiology: Crohn's, volvulus, ischemia, massive resection.
  • Complications: Malnutrition, dehydration, electrolyte imbalance, gallstones, oxalate renal stones.
  • Mgmt: Diet (high calorie/protein, low fat), TPN, octreotide.

High‑Yield Points - ⚡ Biggest Takeaways

• Meckel's diverticulum: Rule of 2s, most common congenital GI anomaly, ectopic gastric mucosa.
• Crohn's disease: Transmural inflammation, skip lesions, cobblestoning, non-caseating granulomas.
• Intussusception: Commonest cause of infant intestinal obstruction, currant jelly stool, target sign (USG).
• Small Bowel Obstruction (SBO): Adhesions (post-op) are leading cause in adults; hernias second.
• Carcinoid tumors: Most common in appendix; carcinoid syndrome with liver metastasis (flushing, diarrhea).
• Celiac disease: Gluten sensitivity causing villous atrophy; anti-TTG antibodies positive_._