Mucinous Adenocarcinoma of the Urachus

Bang Huu Huynh, MD - Case Coordinator
Donnella S Green, MD - Radiology Discussion
Jian Shen, MD, PhD - Pathology Discussion
Steven E Seltzer, MD - Attending Radiologist

May 12, 2003

Presentation

Imaging Findings

An axial T1-weighted MR image shows an iso-intense (to muscle), midline mass just deep to the rectus abdominus. T2-weighted images show that the mass is well-encapsulated; mass effect on the bladder is apparent. The lesion is hyperintense on T2, suggesting the presence of blood products or fluid (although simple fluid would have had a darker appearance on T1). Thin septations are visible. After the introduction of gadolinium, the mass enhances slightly peripherally.

Differential Diagnosis

Diagnosis

Discussion

A partial cystectomy was performed. The specimen shows a tumor mass arising from the urachus to the dome of the bladder. On cross-section, the mass is filled with mucinous material. Even on low-power microscopy, components of adenocarcinoma are apparent in the mucinous material.

Radiology Discussion:

The urachus is a fibrous cord remnant of the urogenital sinus that extends from the urinary bladder to the umbilicus. It is formed during the fourth or fifth month of gestation, when the urogential sinus closes and differentiates to form the bladder (superior portion) and the urethra (inferior portion). Urachal carcinoma is rare, accounting for fewer than 0.7% of bladder cancers. It most commonly arises in the dome of the urinary bladder at the ureterovesicle junction, and often invades the anterior abdominal wall. Approximately 85% are adenocarcinomas, representing 40% of bladder adenocarcinomas. The majority of cases (75%) occur in men, typically between the ages of 40 and 70 years. Most patients have a poor prognosis.

Clinical symptoms of urachal carcinoma include a suprapubic mass, abdominal pain, hematuria (71%), and mucus in the urine. The last occurs in 25% of cases and is considered an almost pathognomonic finding. In 70% of adults, a lumen -- lined by transitional cell epithelium-- remains in the urachus. This may undergo metaplasia leading to carcinoma. The typical result is mucinous adenocarcinoma (75-95%). CT is the preferred modality for diagnosis and evaluation of metastatic disease. Ultrasound may demonstrate a supravesicle mass. Plain radiographs are not particularly useful; although calcifications occur in 4% of cases, they are rarely seen. The differential diagnosis includes primary bladder carcinoma and invasive metastatic adenocarcinoma (rectum, prostate, stomach, ovary, cervix, and uterus).

References

Dunnick NR. Textbook of Uroradiology. Lippincott Williams & Wilkins; 1991.

Dahnert W. Radiology Review Manual, 3rd Ed. Lippincott Williams & Wilkins; 1995.

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