A Case of Abscess in Omentum suspected due to Infected Urachal Remnant Tissue

A 18-year-old was admitted to our hospital because of abdominal pain and high fever. Abdominal ultrasonography and computed tomography showed a cystic mass about 6 cm in diameter, lying near the peritoneum at the midline of the lower abdomen. Following the diagnosis of an infected urachal cyst, resection of the cystic tumor was performed. Adhesions were observed between the rectus abdominis muscle and the peritoneum, and some urachal remnant tissue was found between them. The tumor was an abscess localized by the omentum and adhering tightly to the peritoneum just behind the urachal remnant tissue, which did not have any pathway to the surrounding organs incliding the transverse colon. Because the tumor existed near the dorsal region of the urachal tissue, it was supposed that the infection of the urachal remnant tissue developed into the peritoneal cavity and formed an abscess localized by the omentum, which was confermed by histological examination. It is very seldom, if even, seen that an infected urachal cyst penetrates the abdominal wall and reaches the peritoneal cavity. A localized abscess formation by the omentum caused by an infected urachal remnant tissue has never been reported so far.