Inflammatory bowel disease (IBD) encompasses two chronic, relapsing conditions: Crohn disease (CD) and ulcerative colitis (UC). Crohn disease can affect ANY part of the GI tract from mouth to anus (terminal ileum most common) and involves transmural inflammation (all layers of the bowel wall — mucosa through serosa). This transmural involvement leads to characteristic complications: fistulae (abnormal connections between bowel segments or to skin, bladder, vagina), strictures (fibrotic narrowing from chronic inflammation), and abscess formation. Skip lesions (areas of disease separated by normal bowel) and cobblestone appearance of the mucosa are hallmarks. Non-caseating granulomas are found on biopsy. Ulcerative colitis is limited to the colon and rectum, always involves the rectum (extends proximally in a continuous pattern), and affects only the mucosa and submucosa. UC causes crypt abscesses, pseudopolyps, and a continuous pattern of inflammation without skip lesions. Bloody diarrhea with mucus is the cardinal symptom. Toxic megacolon (colonic dilation >6 cm with systemic toxicity) is a life-threatening complication of UC. Both conditions have extraintestinal manifestations including arthritis, uveitis/iritis, erythema nodosum, pyoderma gangrenosum, primary sclerosing cholangitis (more common in UC),...