SECTION 1: ESOPHAGUS Nonneoplastic Tracheoesophageal Fistula and Esophageal Atresia Esophageal Duplication Cyst Inlet Patch Esophageal Webs and Rings Esophageal Diverticula Esophageal Varices Esophageal Tears and Perforations Achalasia Gastroesophageal Reflux Disease Eosinophilic Esophagitis Pill-Induced Esophagitis Corrosive Damage (Lye) Sloughing Esophagitis Candidal Esophagitis HIV-Associated Esophageal Ulcers Barrett Esophagus Neoplastic Dysplasia in Barrett Esophagus Adenocarcinoma, Esophagus Squamous Papilloma Squamous Dysplasia Squamous Cell Carcinoma, Esophagus Esophageal Liposarcoma/Giant Fibrovascular Polyp Granular Cell Tumor SECTION 2: STOMACH Nonneoplastic Pyloric Stenosis Gastric Antral Vascular Ectasia Dieulafoy Lesion Portal Hypertensive Gastropathy Acute Hemorrhagic Gastritis Chemical Gastropathy Gastric Mucosal Calcinosis Iron Gastropathy Gastric Ulcers Carditis Helicobacter pylori Gastritis Helicobacter heilmannii Gastritis Multifocal Atrophic Gastritis Autoimmune Gastritis Lymphocytic Gastritis Eosinophilic Gastroenteritis Focally Enhanced Gastritis Collagenous Gastritis Granulomatous Gastritis Phlegmonous Gastritis Herpes Zoster Infection Gastric Xanthoma Hyperplastic Polyps, Stomach Ménétrier Disease Zollinger-Ellison Syndrome Neoplastic Fundic Gland Polyp Adenoma/Dysplasia, Stomach Adenocarcinoma, Stomach Adenocarcinoma, Special Variants Molecular Classification of Gastric Cancer Hereditary Diffuse Gastric Cancer Well-Differentiated Neuroendocrine Tumor (Carcinoid), Stomach MALT Lymphoma Gastroblastoma Plexiform Fibromyxoma SECTION 3: SMALL INTESTINE Nonneoplastic Small Intestine Duplication Cyst Meckel Diverticulum Gastric Heterotopia Ectopic Pancreas Microvillus Inclusion Disease Necrotizing Enterocolitis Primary Lymphangiectasia Lymphangioma Peptic Duodenitis/Duodenal Ulcer Celiac Disease Tropical Sprue Bacterial Overgrowth/Stasis Olmesartan Enteropathy Autoimmune Enteropathy Pouchitis Whipple Disease Common Variable Immunodeficiency Giardia Cryptosporidia Cystoisospora (Isospora) Cyclospora Microsporidia Yersinia Mycobacterium avium-intracellulare Mycobacterium tuberculosis Strongyloides Neoplastic Adenoma, Small Intestine Adenocarcinoma, Small Intestine Well-Differentiated Neuroendocrine Tumor (Carcinoid), Small Intestine Gangliocytic Paraganglioma Enteropathy-Associated T-Cell Lymphoma Follicular Lymphoma, Duodenal Type Gastrointestinal Tract Clear Cell Sarcoma-Like Tumor Waldenström Protein SECTION 4: APPENDIX Nonneoplastic Acute Appendicitis Granulomatous Appendicitis Enterobius vermicularis Appendicitis Fibrous Obliteration Neoplastic Serrated Polyps, Appendix Appendiceal Mucinous Neoplasms Well-Differentiated Neuroendocrine Tumor (Carcinoid), Appendix 358 Goblet Cell Adenocarcinoma SECTION 5: COLON Nonneoplastic Hirschsprung Disease Colonic Duplications, Cysts, and Congenital Diverticula Motility Disorders Diverticular Disease Endometriosis Preparation Artifacts Melanosis Coli Ulcerative Colitis, Colon Crohn Disease Lymphocytic Colitis Collagenous Colitis Eosinophilic/Allergic Colitis Diversion Colitis Diverticular Disease-Associated Colitis Solitary Rectal Ulcer Syndrome/Mucosal Prolapse Pneumatosis Cystoides Intestinalis Sexually Transmitted Proctitis Acute Infectious Colitis Focal Active Colitis Campylobacter Salmonella Shigella Clostridium difficile Enterohemorrhagic Escherichia coli Spirochetosis Adenovirus Malakoplakia Histoplasma Cryptococcus Entamoeba histolytica Schistosomiasis Neoplastic Benign Fibroblastic Polyp/Perineurioma Ganglioneuroma Hyperplastic Polyps, Colon Sessile Serrated Lesion (Adenoma/Polyp) Mixed Adenoma-Serrated Polyp Adenoma, Colon Adenoma With Pseudoinvasion Adenoma With Invasive Carcinoma Colorectal Adenocarcinoma Familial Cancer Syndromes in Colorectal Carcinoma Familial Adenomatous Polyposis Lynch Syndrome (Hereditary Nonpolyposis Colorectal Cancer Syndrome) Serrated Polyposis Hereditary Mixed Polyposis Syndrome Inflammatory Bowel Disease-Associated Neoplasia Well-Differentiated Neuroendocrine Tumor (Carcinoid), Colon Mastocytosis SECTION 6: ANUS Nonneoplastic Hemorrhoids Tailgut Cyst Neoplastic Anal Intraepithelial Neoplasia Squamous Cell Carcinoma, Anus Basal Cell Carcinoma Paget Disease Anal Duct Carcinoma HPV-Associated Anorectal Adenocarcinomas SECTION 7: MULTIPLE ORGANS Nonneoplastic Amyloidosis Cytomegalovirus Herpes Simplex Virus Nonsteroidal Antiinflammatory Drug (NSAID) Damage Ischemia Vasculitis Behçet Syndrome Graft-vs.-Host Disease Mycophenolate Injury Radiation Effect Immune Modulator Therapy Effect Chemotherapy Effect Taxane Effect Colchicine Toxicity Kayexalate Injury Cowden/PTEN Hamartoma Tumor Syndrome Hamartomatous Polyps, Cronkhite-Canada Hamartomatous Polyps, Juvenile Hamartomatous Polyps, Peutz-Jeghers Neoplastic Leiomyoma Leiomyosarcoma Gastrointestinal Stromal Tumor Mesenteric Fibromatosis Inflammatory Fibroid Polyp Schwannoma Inflammatory Myofibroblastic Tumor Glomus Tumor Primary Melanoma Metastatic Melanoma Large B-Cell Lymphomas Mantle Cell Lymphoma Lipomatous Tumors Follicular Dendritic Cell Sarcoma Synovial Sarcoma of Gastrointestinal Tract