Pseudomyxoma Retroperitonei: ARare Cause of Retroperitoneal Cystic Mass.

: Pseudomyxoma retroperitonei is a rare condition, characterized by accumulation of mucinous material in the retroperitoneal space, originating predominantly from the appendiceal mucinous neoplasms. A72-year-old male patient presented with a history of progressive right side abdominal pain for 5 months with a palpable abdominal mass. Ultrasound, computerized tomography, and magnetic resonance imaging showed large right abdominal multiloculated cystic lesion with heterogeneous echoic contents. Colonoscopy revealed normal mucosa with extramural pressure on the right colon and cecum. He underwent complete excision of the mass along with right hemicolectomy. The cystic mass was containing gelatinous material. Histopathology revealed low grade mucinous neoplasm. Pseudomyxoma retroperitonei should be considered in the differential diagnosis of patient presenting with progressive right side abdominal pain and retroperitoneal cystic mass.