GASTROINTESTINAL PATHOLOGY (Part 2)

## Summary This document provides essential notes on gastrointestinal pathology, focusing on conditions of the small and large intestines and the peritoneal cavity, comprising Part 2 of 2. It covers intestinal obstruction (Hirschsprung disease, hernias), vascular disorders (ischemic bowel disease, hemorrhoids), various forms of malabsorptive diarrhea (celiac disease, Crohn disease, tropical sprue, Whipple disease), and a comprehensive overview of infectious enterocolitis caused by bacteria (cholera, Shigella, E. coli, Salmonella, C. difficile), viruses (Rotavirus), and parasites (Giardiasis, Cryptosporidiosis, Amoebiasis, Hookworms, Strongyloidiasis). Additionally, it details inflammatory intestinal diseases like appendicitis and inflammatory bowel disease (Crohn disease, Ulcerative Colitis), and discusses neoplasms including colorectal adenomas and adenocarcinomas, and appendiceal carcinoid. The final section addresses ascites in the peritoneal cavity, outlining its pathophysiology. A high-yield exam summary provides key facts across all covered topics. ## Key Points - **Aphthous ulcers:** Up to 40% population; associated with coeliac, IBD, Behçet; resolve 7–10 days - **HSV oral:** Multinucleated polykaryons + eosinophilic intranuclear inclusions - **Oral candidiasis:** Scrapes off (unlike leukoplakia); pseudomembranous = most common form - **Leukoplakia vs erythroplakia:** Erythroplakia has MUCH higher malignant transformation risk (>50%) - **Oral SCC:** 95% of oral cancers; two pathways: tobacco/alcohol vs HPV-16; field cancerisation - **HPV oral SCC:** Tonsillar crypts/tongue base; better prognosis; overexpresses p16 - **Xerostomia:** Medications most common cause; >20% over age 70; Sjögren hallmark - **Mumps:** Parotids; orchitis in adults → sterility - **Mucocele:** Most common salivary inflammatory lesion; lower lip; blockage/rupture of duct - **Oesophageal varices:** 90% of cirrhotics; 50% die from first bleed; alcoholic cirrhosis most common - **Mallory-Weiss vs Boerhaave:** Superficial/mucosal vs transmural + mediastinitis - **GERD morphology:** Eosinophils first → neutrophils; basal zone hyperplasia >20%; papillae elongation - **Barrett oesophagus:** Goblet cells define intestinal metaplasia; 10% of symptomatic GERD - **Achalasia:** Triad: incomplete LES relaxation + ↑LES tone + aperistalsis; Chagas = secondary - **Oesophageal SCC vs adenocarcinoma:** SCC: middle third; alcohol + tobacco; adenocarcinoma: distal third; Barrett - **H. pylori virulence:** Flagella, urease, adhesins, CagA toxin - **H. pylori vs Autoimmune gastritis:** H. pylori = antrum, ↑acid; Autoimmune = body/fundus, achlorhydria, pernicious anaemia - **Cushing vs Curling ulcers:** Cushing = intracranial disease, high perforation risk; Curling = burns/trauma, proximal duodenum - **Zollinger-Ellison:** Gastrinoma → massive acid → ulcers even in jejunum - **PUD pain:** 1–3 hours after meals; relieved by alkali or food - **GIST:** c-KIT or PDGFRA mutations; interstitial cells of Cajal; imatinib - **Hirschsprung:** RET mutation; aganglionosis; always involves rectum; absent ganglion cells on biopsy - **Ischaemic bowel:** Watershed zones: splenic flexure + rectosigmoid; surface necrosis + hyperproliferative crypts - **Reperfusion injury:** Greatest damage occurs at reperfusion not at initial ischaemia - **Coeliac disease:** HLA-DQ2/DQ8; anti-tissue transglutaminase most sensitive; dermatitis herpetiformis 10%; enteropathy-associated T cell lymphoma - **Cholera:** Cholera toxin → ↑cAMP → CFTR opens → Cl⁻ secretion; non-invasive; fluid replacement saves >99% - **Shigella:** Infective dose <100 organisms; Shiga toxin → HUS; no antidiarrhoeals - **Typhoid:** Rose spots; Peyer patch enlargement; typhoid nodules in liver; gallbladder chronic carrier state; sickle cell → osteomyelitis - **C. difficile:** Volcano pattern pseudomembranes; treat with metronidazole/vancomycin; no antidiarrhoeals - **Rotavirus:** 6–24 months; destroys mature enterocytes; breast milk antibodies protect first 6 months - **Hookworms:** Leading cause iron deficiency anaemia in developing world - **Giardia:** Pear-shaped trophozoites; evades immunity by variant surface protein; decreases lactase - **Acute appendicitis:** Diagnosis requires neutrophil infiltration of muscularis propria; McBurney's sign; faecalith 50–80% - **Appendix carcinoid:** Almost always benign; distal tip; pseudomyxoma peritonei from adenocarcinoma - **FAP vs HNPCC:** FAP: APC mutation, >100 polyps, cancer <30; HNPCC: mismatch repair genes, fewer polyps - **Colorectal adenocarcinoma:** Two most important prognostic factors: depth of invasion + lymph node metastases - **Ascites:** Cirrhosis triad: ascites, encephalopathy, bleeding varices; RAAS activation; Child-Pugh score ## Detailed Notes ## SECTION 4: SMALL AND LARGE INTESTINES **Conditions covered:** Intestinal Obstruction · Vascular Disorders · M