Editors: Francesca Khani ( and Mahmut Akgul (

2022-01/January 3
Contributors: Aysha Mubeen and Cristina Magi-Galluzzi

A woman in her mid-60s with history of uterovaginal prolapse, status post hysterectomy, was incidentally noted to have a patent urachus at the bladder dome on cystourethroscopy. A CT scan showed a partially distended urinary bladder with a small vesicourachal diverticulum and focal calcifications at its apex. Partial cystectomy with excision of the entire urachus was performed. Gross examination showed a 3.2 cm cystic nodule with calcified cut surface. Images from the partial cystectomy are shown below.


What is the correct diagnosis?

a. Mucinous cystadenoma

b. Villous adenoma

c. Mucinous cystic tumor of low malignant potential

d. Mucinous adenocarcinoma

e. Urothelial carcinoma

Mucinous cystic tumor of low malignant potential involving a urachal diverticulum

This was a cystic tumor involving a a urachal diverticulum (image 1). There are focal areas where the cyst wall epithelium shows a single layer of mucinous cells (image 2) that would have been in keeping with mucinous cystadenoma. However, there are other areas, with nuclear stratification and low-grade atypia (image 3, 4 and 5) that upgraded this tumor to a mucinous cystic tumor of low malignant potential. There were also extensive calcifications and osseous metaplasia (image 6). The bladder mucosa showed reactive changes. No areas of microinvasion or intraepithelial carcinoma were identified. The margins of resection were negative for tumor.

The urachus is an embryologic structure that connects the urinary bladder to the allantois and obliterates in infancy to form the median umbilical ligament.

Urachal remnants may persist in the form of patent urachus, urachal diverticulum, urachal sinus, or urachal cyst. Tumors that arise in the urachal remnants can be glandular (adenomas, mucinous cystic tumor of low malignant potential, adenocarcinomas) or non-glandular (urothelial carcinoma, squamous cell carcinoma etc.).

Mucinous tumors of the urachus are rare lesions. The proposed classification is analogous to the one used for ovarian mucinous tumors. In a series of 55 glandular neoplasms of the urachus, the majority of the mucinous cystic tumors were in the category of mucinous cystic tumors of low malignant potential. No recurrence or metastasis occurred in the 13 mucinous cystic tumors where follow up was available (including the intraepithelial and invasive carcinomas).

1. WHO Classification of Tumours of the Urinary System and Male Genital Organs. 4th ed. Lyon, France: IARC Press; 2016:113–114.

2. Paner GP, Lopez-Beltran A, Sirohi D, Amin MB. Updates in the pathologic diagnosis and classification of epithelial neoplasms of urachal origin. Adv Anat Pathol. 2016;23(2):71–83.

3. Amin MB, Smith SC, Eble JN, et al. Glandular neoplasms of the urachus: a report of 55 cases emphasizing mucinous cystic tumors with proposed classification. Am J Surg Pathol. 2014; 38:1033–1045.

Aysha Mubeen
Brigham and Women’s Hospital

Cristina Magi-Galluzzi
University of Alabama at Birmingham


Urachus, mucinous tumor, bladder adenocarcinoma