Gastrointestinal & Hepatobiliary Command Center
High-yield GI luminal pathology, Crohn vs. Ulcerative Colitis differentiation, complete viral hepatitis serology matrix, cirrhosis and portal hypertension therapeutics, serum ascites albumin gradient (SAAG), acute pancreatitis, and pediatric GI surgical emergencies.
Crohn Disease vs. Ulcerative Colitis Master Decoder
| Feature | Crohn Disease | Ulcerative Colitis (UC) | Board Pivot Point |
|---|---|---|---|
| Anatomical Location | Any part of GI tract (mouth to anus); terminal ileum and colon most common; rectal sparing. | Colon and rectum ONLY; begins in rectum and extends proximally in a continuous fashion without skip lesions. | Rectal sparing = Crohn; Continuous rectal involvement = UC. |
| Gross Lesion Pattern | Skip lesions; "cobblestone" mucosal architecture; bowel wall thickening with "creeping fat"; strictures ("string sign" on barium). | Continuous mucosal erythema, friability, ulceration, and pseudopolyps; loss of haustra ("lead pipe" sign on barium). | Skip lesions & creeping fat are pathognomonic for Crohn. |
| Depth of Inflammation | Transmural (Entire wall) → leads to fistulas, abscesses, perforations. | Mucosa and Submucosa ONLY (Superficial). | Fistulas (enterovesical, enterocutaneous) only occur in Crohn due to transmural depth! |
| Histopathology | Non-caseating granulomas containing multinucleated giant cells; lymphoid aggregates. | Crypt abscesses and crypt architectural distortion with neutrophils in crypt lumens; NO granulomas. | Non-caseating granulomas rule in Crohn; Crypt abscesses rule in UC. |
| Stool Characteristics | Non-bloody watery diarrhea (unless colon heavily involved); malabsorption and steatorrhea. | Bloody diarrhea (hematochezia), tenesmus, and fecal urgency. | Bloody diarrhea + tenesmus = classic UC presentation. |
| Serology & Associations | + ASCA (Anti-Saccharomyces cerevisiae antibodies); calcium oxalate kidney stones (terminal ileum fat malabsorption binds Ca2+ leaving free oxalate). | + p-ANCA (perinuclear antineutrophil cytoplasmic antibodies); Primary Sclerosing Cholangitis (PSC). | PSC + p-ANCA is strongly tied to UC (causes "onion-skin" bile duct fibrosis). |
| Lethal Complications | Strictures / bowel obstruction, enterovesical fistulas (pneumaturia/fecaluria), gallstones. | Toxic Megacolon (> 6 cm dilation + systemic toxicity); high colorectal carcinoma risk. | Toxic megacolon requires immediate NPO, IV steroids, antibiotics, and possible colectomy! |
Crohn Disease: Non-Caseating Granuloma
Biopsy Hallmark: Epithelioid histiocytes and multinucleated Langhans-type giant cells without central necrosis (non-caseating), found in up to 60% of transmural resection specimens.
Extraintestinal Manifestations: Aphthous stomatitis, erythema nodosum, pyoderma gangrenosum, peripheral arthritis, ankylosing spondylitis (HLA-B27), kidney stones (calcium oxalate).
Ulcerative Colitis: Lead Pipe & Crypt Abscesses
Radiology Clue: Chronic inflammation and muscle hypertrophy lead to complete loss of colonic haustrations, giving the colon a smooth, rigid "lead pipe" appearance on barium enema.
Surveillance Requirement: Annual screening colonoscopies beginning 8 years after initial diagnosis of pancolitis due to high colorectal adenocarcinoma risk.
Esophageal Motility & Perforations
Pathology: Loss of inhibitory ganglion cells (nitric oxide and VIP producing) in myenteric (Auerbach) plexus in lower esophagus.
Presentation: Progressive dysphagia to both solids AND liquids; regurgitation of undigested food.
Diagnostics: High-resolution manometry (incomplete LES relaxation + aperistalsis) & Barium swallow showing "bird's beak" tapering.
Pathophysiology: Uncoordinated, non-peristaltic, simultaneous contractions of the esophageal smooth muscle.
Presentation: Episodic severe retrosternal chest pain and dysphagia triggered by hot or cold liquids; mimics angina/myocardial infarction.
Workup & Rx: Barium swallow demonstrates "corkscrew esophagus"; treat with calcium channel blockers or nitrates.
Pathology: False (pulsion) diverticulum herniating through an anatomical area of weakness (Killian triangle) between thyropharyngeus and cricopharyngeus muscles.
Triad: Dysphagia, halitosis (foul breath from decaying trapped food), and a palpable neck mass that gurgles.
Board Warning: Nasogastric tube insertion or upper endoscopy is strictly contraindicated due to high perforation risk!
Mechanism: Transmural esophageal perforation (usually left posterolateral wall of distal esophagus) caused by sudden severe increase in intragastric pressure (violent retching/vomiting).
Mackler Triad: Vomiting, lower thoracic chest pain, and subcutaneous emphysema (crepitus on chest palpation); Hamman sign (mediastinal crunch).
Diagnosis: Gastrografin (water-soluble) esophagram; barium is contraindicated due to chemical mediastinitis.