Small intestine and ampulla can be involved in a heterogeneous group of benign tumors and tumor-like diseases, potentially mimicking malignant neoplasms. In-depth knowledge of them is critical for practicing pathologists since they represent potential pitfalls in routine diagnostic activity. Such conditions include the following: (1) Brunner gland lesions, including Brunner gland hyperplasia and hamartoma; (2) polyps, such as adenoma, hyperplastic, hamartomatous, and inflammatory; (3) mesenchymal proliferations encompassing inflammatory fibroid polyp, inflammatory myofibroblastic tumor, leiomyomas, lipomas, and lipomatosis of the ileocecal valve; (4) fibrosis-associated diseases, such as idiopathic retroperitoneal fibrosis, reactive nodular fibrous pseudotumor, and sclerosing peritonitis; (5) disorders of lymphatic vessels, including lymphangiectasia and lymphangiomas; and (6) other rare conditions/miscellanea, such as enteritis cystica profunda, intussusception, ischemia, and pneumatosis cystoides intestinalis. This review, inspired by the content of the PathologyOutlines website (https://www.pathologyoutlines.com), aims to provide a reference point in this complex scenario, summarizing the essential histopathological features of all these entities for better addressing routine practice and differential diagnoses.
Keywords: Vater; ampulla; duodenum; ileum; small intestine.