Heterotopic gastrointestinal mucosa and pancreatic tissue in a retroperitoneal tumor.

We believe that this is the first report of a retroperitoneal tumor consisting of heterotopic gastrointestinal mucosa and pancreatic tissue. The patient was a 19-year-old woman with the chief complaint being occasional back pain. Abdominal computerized tomography demonstrated a 3.1 x 2.5 x 3.2-cm low-density solid and cystic lesion adjoining the left renal vein between the aorta and inferior vena cava. Angiography revealed that the inferior vena cava was displaced by the hypovascular tumor. The retroperitoneal lesion was diagnosed preoperatively as a benign tumor such as a neurogenic neoplasm or lymphangioma. At laparotomy, a cystic tumor was found, which existed behind the inferior vena cava and renal vessels, and contained reddish-brown fluid, suggesting hemorrhage in the past. The cut surface of the tumor showed a unilocular cyst with partially hypertrophic wall. Histopathological examination revealed a cystic tumor lined with heterotopic gastric and duodenal mucosa, with pancreatic tissue in the muscularis propria. In addition, evidence of bleeding from the gastric mucosa was observed in the cystic tumor. External secretion from these tissues could have triggered the hemorrhage and expanded the tumor, possibly resulting in the back pain.