Urachal tumors are exceedingly rare, accounting for less than 1% of all bladder-related malignancies. Among them, low-grade mucinous cystic tumors of urachal origin are particularly uncommon and poorly characterized. We present a rare case of a low-grade mucinous cystic tumor arising from the urachus, accompanied by a brief review of the relevant literature.

The patient is a 51-year-old man who visited our hospital’s Department of Gastroenterology with the chief complaint of an abdominal mass noted during an abdominal ultrasound examination conducted as part of a routine health checkup. A contrast-enhanced CT scan, performed for further investigation, revealed a multilocular cystic mass contiguous with the bladder, containing calcifications and areas of solid components within the wall. The findings suggested a urachal cyst with suspected malignancy, and the patient was referred to our department.

On physical examination, a soft mass was palpable in the lower abdomen without associated pain. Laboratory data showed no notable abnormalities, and various tumor markers were negative. MRI findings were consistent with the CT scan, showing a multilocular cystic tumor. Given the suspicion of a malignant urachal cyst, surgical excision of the urachal cyst was performed via open surgery. The tumor was well demarcated from the surrounding tissues and had a smooth surface. It contained yellowish-white mucinous material internally. Histopathological examination revealed no definitive signs of malignancy, and the diagnosis was a low-grade mucinous tumor.

Urachal mucinous tumors are extremely rare benign diseases. However, complications such as pseudomyxoma peritonei have been reported, and strict follow-up is considered necessary due to the potential for malignancy. Urachal tumors are extremely rare, with only 41 cases reported in the literature up to 2023. Surgical resection is the mainstay of treatment, and recurrence is considered uncommon. However, pseudomyxoma peritonei has been reported in four cases. When complete resection is achieved, the 10-year survival rate is approximately 70%. In contrast, incomplete resection is associated with a 10-year survival rate of less than 20%, underscoring the importance of complete surgical removal.