Retroperitoneal mass, a rare manifestation of mucinous adenocarcinoma of appendix: A case report.

The retroperitoneum (RP) might be affected by a variety of infections, inflammations, and tumors, including benign and malignant ones. Although primary malignant tumors are the most prevalent ones in this anatomic area, metastatic and invasive tumors rarely involve the retroperitoneum. Gastrointestinal stromal tumors (GISTs) are considered as the most common tumors that invade the retroperitoneum, but, to the best of our knowledge, it is the first time a surgery team has encountered the appendiceal tumor as a huge retroperitoneal mass. A 68-year-old man was referred to the emergency department with abdominal distension and weight loss. In his course of hospitalization, a huge right retroperitoneal mass was detected by a computed tomography (CT) scan; after that, the patient underwent laparotomy, evacuation of massive mucinous tissue located in the right retroperitoneum, and right hemicolectomy due to appendiceal tumor. The histopathological examination showed "mucinous appendiceal neoplasm." This is the first case study showing the invasion of an appendiceal tumor through the visceral peritoneum into the retroperitoneum, so an invasion of the peritoneal tumor to the retroperitoneum should be considered when a urologist approaches retroperitoneal masses.