Retroperitoneal cysts are uncommon, with an estimated incidence of 1/5750 to 1/250,000 .
A 54 year old female patient presented to Al-Karama Teaching Hospital with sensation of
mild left lower abdominal pain colicky in nature with mild backache , ten days duration. No dysuria, normal bowel motion .
On physical examination we palpated a fixed mass in the left lateral side of abdomen.
Ultrasound revealed thin walled large cystic mass ,CT-scan showed large regular cystic mass in left side of abdominal retroperitoneum .
During the operation we found a retroperitoneal cyst at the lateral side of sigmoid colon and extend posterior to the descending colon . The cyst arising within the retroperitoneum outside the major organs.
CT scan, and MRI help in confirming the diagnosis, but surgery is the keystone in confirming the diagnosis, and surgery remains the best treatment option.