Table 3.

Different subtypes of duodenal polyposis and sporadic duodenal polyp

Subtypes [references]	Age of onset (years)	Common duodenal distribution	Endoscopic appearance	Histological characteristics	Immunohistochemical markers
Brunner’s gland hamartoma [2, 3, 7, 26]	50–70	Duodenal bulb and descending	Pedunculated/sessile polyp	Mixture of Brunner’s glands, ducts, smooth muscle, fibrous tissue, adipose tissue, lymphocytes, etc.	MUC6 (+)
Gastric heterotopia [40, 41]	NA	Duodenal bulb and descending	Isolated or multiple submucosal masses	Lesions consisting of gastric glands covered by normal duodenal mucosa	β-catenin (+)
Inflammatory fibroid polyp [42]	50–80	NA	Isolated polyp with smooth mucosa	Spindle-shaped cells proliferation with infiltration of small blood vessels and eosinophilic inflammation	Vimentin (+), CD34 (+)
Lipoma [43, 44]	50–80	Duodenal descending	Isolated/rarely multiple, pedunculated/sessile, round/oval, and soft mass with normal surface mucosa, which may have areas of erosion or ulceration	Mature adipose tissue arranged in lobules	CD34 (+)a, desmin (−), S100 protein (−), STAT6 (−), SMA (−)
Leiomyoma [45, 46]	60–80	NA	Lobular mass with a boundary that is well-defined/irregular/interdigitating with normal smooth muscle	Mature smooth muscle cells with hyaline degeneration, coagulative necrotic stroma, and low mitotic activity	SMA (+), desmin (+), S100 (−), Ki-67 (−), CD34 (−), HMB4 (−)
Carcinoid [47, 48]	No age predilection	Proximal duodenum	Intraluminal polypoid/mural mass	Endocrine secretion granules observed by a characteristic silver affinity	Serotonin (+), gastrin (+), somatostatin (+)
Gastrointestinal stromal tumor [42, 49, 50]	50–65	Duodenal descending	Smooth submucosal mass with ulceration and bleeding areas on the surface	Most are spindle cell tumors with palisade nuclei, half are mixed with skeinoid fibers, and more than 20.0% are accompanied by hemangioma-like vascular proliferation	CD117 (+): 95.0% CD34 (+): 70.0%
Lymphoma [42, 51]	50–60	Proximal duodenum	Multiple small, rough polyps or nodules	Different histological patterns: diffuse large B cell, mucosa-associated lymphoid tissue, mantle cell, and Hodgkin’s and follicular lymphoma	CD20 (+)b, CD10 (+), Bcl-2 (+), BCL6 (+), low Ki-67 index
Non-ampullary sporadic adenoma [42, 52]	60–90	Distal duodenum	Isolated sessile polyp	Mostly tubular crypts with hyperchromatic, enlarged, and pseudostratified nuclei	Cytokeratin 7 (+), cytokeratin 20 (+)
Familial adenomatous polyposis [52–54]	20–40	Duodenal descending and horizontal, peri-ampullary	Multiple flat polyps	Tubular or tubulovillous crypts mixed with columnar epithelial cells, goblet cells, paneth cells, and endocrine cells, accompanied by enlarged and elongated hyperchromatic nuclei	Cytokeratin 7 (+), cytokeratin 20 (+)
Peutz-Jeghers syndrome [55–57]	10–30	NA	Isolated/multiple polypoid lesions	Branched villous structures containing smooth muscle core and multiple types of cells	Serotonin (+)
Solitary Peutz-Jeghers polyp [56–58]	NA	NA	Isolated, pedunculated/rarely sessile, polypoid lesion	Branched villous structures containing smooth muscle core and multiple types of cells	Serotonin (+)

NA not available

^aThe immunohistochemical marker we describe here is the histologic pattern of spindle cell/pleomorphic lipoma

^bThe immunohistochemical marker we describe here is the histologic pattern of follicular lymphoma