Gastric hamartomatous inverted polyp mimicking ectopic pancreas on endoscopy and endosonography.

Gastric hamartomatous inverted polyp (HIP) is difficult to diagnose preoperatively because of its rarity [1,2]. It is pathologically benign, but has been reported as a paracancerous lesion [3–5], and therefore its diagnosis and treatment are clinically important. We report a case of gastric HIP and focus on its special characteristics on endoscopy and endosonography. An 18-mm submucosal tumor with whitish mucus flowing out from a central orifice was an incidental finding in the posterior wall of the gastric fundus in a 23-year-old woman (●" Fig.1). Endoscopic ultrasonography (20MHz) revealed a heterogeneous tumor arising from the third layer of the gastric wall with a cystic portion inside (●" Fig.2a). A 3.2mm anechoic duct communicated between the surface and the cystic portion (●" Fig.2b). Injection-assisted endoscopic mucosal resection was performed. Pathological analysis revealed overlying gastric mucosa with submucosal proliferation of cystic glands and smooth muscle bundles (●" Fig.3a). The submucosal components connected with the overlying mucosa through a mucus-filling drainage duct (●" Fig.3b). Immunohistochemical staining with actin demonstrated smooth muscle proliferation within the polyp (●" Fig.3c). This picture was compatible with the diagnosis of gastric HIP. To our knowledge, this is the first report of a gastric HIP with mucus secretion from its central orifice on endoscopy and an anechoic duct on endosonography. Ectopic pancreases, carcinoid tumors, and hamartomatous polyps could manifest as central dimpling or umbilication on endoscopy. Occasionally, large gastrointestinal stromal tumors or leiomyomas also have a similar central depression or necrosis, due to insufficient blood supply [6]. However, mucus secretion and ductal structure on the image, corresponding to a drainage duct, are generally only seen in ectopic pancreases [7]. More than 90% of gastric ectopic pancreases are located in the antrum, which is different from our case [8]. Gastric HIP should therefore be considered as a possible diagnosis in cases of submucosal tumors located in the upper stomach, which have the potential to mimic ectopic pancreases.