The vanishing duodenal polyp: mesenteric invagination presenting as duodenal pseudopolyp

Duodenal polypoid masses are an uncommon finding mainly diagnosed incidentally at endoscopy or surgery. We report a 39-year-old female patient with symptoms of intermittent stabbing pain in the upper right abdominal quadrant and an iron deficiency anaemia, without complaints of weight loss, haematemesis or melaena. A duodenal polyp and acute duodenitis have been described during endoscopic examinations and CT and ultrasound. Surgical excision of the polyp was advised. Intraoperatively, an elongated duodenum was remarkable; however, at duodenotomy, no polyp was found, nor during intraoperative endoscopy. Looking back at the endoscopy and imaging results, it was noted that the polyp varied in size and location. It was therefore concluded that we dealt with the pseudopolyp phenomenon, caused by invagination of the duodenal wall and its mesentery into the duodenum, presenting as a lipomatous pseudopolyp. Telescopic invagination of the duodenal wall was facilitated by the elongated hypermobile duodenum.