GASTROINTESTINAL PATHOLOGY (Part 1)

GASTROINTESTINAL PATHOLOGY (Part 1) ## Summary This document provides essential notes on **gastrointestinal pathology**, focusing on the **oral cavity**, **oesophagus**, and **stomach**. It covers common inflammatory lesions in the oral cavity, such as **aphthous ulcers**, **HSV infections**, and **candidiasis**, alongside proliferative and neoplastic lesions like **leukoplakia**, **erythroplakia**, and **oral squamous cell carcinoma**. Diseases of the salivary glands, including **xerostomia**, **mumps**, **mucoceles**, and **bacterial sialadenitis**, are also addressed. For the oesophagus, conditions discussed range from congenital anomalies and motility disorders (e.g., **achalasia**, **hiatal hernia**) to inflammatory oesophagitis (**infectious**, **reflux**, **eosinophilic**) and the premalignant **Barrett oesophagus**. The section on the stomach details **acute and chronic gastritis** (**H. pylori** and **autoimmune**), **peptic ulcer disease**, and various gastric tumours, including **adenocarcinomas**, **lymphomas**, **carcinoid tumours**, and **gastrointestinal stromal tumours (GISTs)**. ## Key Points ### Oral Inflammatory Lesions **Aphthous ulcers** (canker sores) are common, painful, recurrent, and of unknown cause. **Herpes Simplex Virus (HSV)** infections (cold sores) are reactivations, showing **intranuclear inclusions** and **multinucleated giant cells**. **Oral Candidiasis** (thrush) is a fungal infection, typically appearing as grey-to-white membranes that **can be scraped off**, distinguishing it from leukoplakia. ### Oral Proliferative and Neoplastic Lesions **Leukoplakia** is a white patch that **cannot be scraped off** and is considered precancerous (5-25% progress to SCC) . **Erythroplakia** is a red, velvety area with a **much greater risk of malignant transformation** (>50%). **Oral Squamous Cell Carcinoma (SC C)** accounts for 95% of oral cancers, is aggressive, and is linked to "**field cancerisation**." It has two main pathways: tobacco/alcohol (**TP53 mutations**) and **HPV-related** (**HPV-16**, **p16 overexpression**, better prognosis). ### Salivary Gland Diseases **Xerostomia** (dry mouth) is common, often drug-induced or seen in **Sjögren syndrome**. **Mumps** is a viral sialadenitis (paramyxovirus), primarily affecting parotids, and can cause **pancreatitis** or **orchitis** in adults. A **mucocele** is the most common inflammatory salivary lesion, resulting from duct blockage/rupture, typically on the lower lip. ### Oesophageal Motility and Congenital Disorders **Oesophageal atresia** is a congenital anomaly (blind pouch), often with a **tracheoesophageal fistula**, posing an aspiration risk. **Achalasia** involves incomplete LES relaxation, increased LES tone, and aperistalsis, characterized by a "**bird's beak**" appearance on barium swallow. ### Oesophageal Inflammation **Infectious oesophagitis** affects immunocompromised patients: **HSV** causes "**punched-out**" ulcers with viral inclusions and giant cells; **CMV** causes shallower ulcers with nuclear and cytoplasmic inclusions; **Candida** causes adherent grey-white pseudomembranes. **Reflux Oesophagitis (GERD)** is the most frequent cause, leading to mucosal injury from gastric acid; histology shows **eosinophils**, **basal zone hyperplasia** (>20%), and elongated papillae. **Eosinophilic Oesophagitis** is characterized by large numbers of eosinophils in the oesophageal epithelium (especially superficially and away from the GEJ), often resistant to PPIs and associated with **atopy**. ### Barrett Oesophagus A complication of chronic GERD, **Barrett oesophagus** is defined by **intestinal metaplasia** within the oesophageal squamous mucosa, significantly increasing the risk of **oesophageal adenocarcinoma**. ### Gastritis **Acute gastritis** involves inflammation without mucosal injury (e.g., NSAIDs, alcohol, stress); severe cases can lead to **acute haemorrhagic erosive gastropathy**. **Chronic gastritis** is characterized by mucosal inflammation, atrophy, and metaplasia. **H. pylori Gastritis:** This is the most common chronic gastritis, predominantly affects the **antrum**, is associated with increased acid secretion, and can lead to **PUD**, **MALT lymphoma**, and **adenocarcinoma**. **Autoimmune Gastritis:** This affects the **body and fundus**, is associated with **anti-parietal cell** and **anti-intrinsic factor antibodies**, leading to **achlorhydria** (decreased acid) and **hypergastrinemia**. It is a major cause of **pernicious anaemia** and increases gastric cancer risk. ### Peptic Ulcer Disease (PUD) **Peptic Ulcer Disease (PU D)** is most often associated with **H. pylori infection** or **NSAID use**, commonly found in the gastric antrum and first portion of the duodenum (**duodenal ulcers are 4x more common**). It is characterized by "**punched-out**" defects, pain relieved by alkali or food, and complications including haemorrhage and perforation. **Zollinger-Ellison syndrome** causes m