Tumors arising in the urachus are generally classified into two categories: benign and malignant. Urachal mucinous tumors with features morphologically similar to ovarian and appendiceal borderline tumors are extremely rare. Only four cases have been reported in the English literature.6
The authors of those cases raised the possibility that, as in ovarian and appendiceal borderline tumors, there is a transitional stage of mucinous carcinogenesis from benign to intraepithelial or infiltrative carcinoma, and those reported cases could represent the premalignant phase in this progression sequence. That hypothesis is also supported by other reports that urachal adenomas may coexist with in situ
and invasive adenocarcinoma.10
All mucinous tumors, regardless of the source, should be accepted as having an aggressive biological potential such as local recurrence and the development of pseudomyxoma peritonei.12
Therefore, it is not surprising that a urachal adenoma with numerous mucinous implants, although histologically benign, might lead to death.13
A recent report described a complex mucinous cystadenoma of undetermined malignant potential on the basis of only extensive mucin extravasation into perivesical soft tissue, even in the absence of dysplasia in the lining of the epithelium and pseudomyxoma peritonei.5
Characteristics of the so-called borderline urachal mucinous tumors reported thus far are listed in . All the cases described marked nuclear pleomorphism, stratification, and various degrees of mitoses in the lining epithelium but no stromal invasion. Two cases revealed the occurrence of pseudomyxoma peritonei, which required adjuvant therapy such as intraperitoneal lavage in addition to surgical removal. However, complete surgical excision was of paramount importance, as it was in the benign tumors. No recurrence was found in all of those cases, although there were limitations that the number of cases was too small to be representative and the follow-up periods were not long enough. Notably, the patient of our case was in the third decade, whereas the other reported ones were in their sixth to eighth decades.
Reported cases of urachal mucinous tumors with uncertain malignant potential
The differential diagnosis of urachal mucinous tumor of uncertain malignant potential includes villous adenoma, urachal mucinous adenocarcinoma, urothelial malignancy with components of adenocarcinoma, and metastatic mucinous tumor from a variety of body sites including breast, pancreas, ovary, prostate gland, and gastrointestinal tract. Villous adenoma is a benign glandular neoplasm lined by pseudostratified columnar epithelium and is characterized by papillary architecture instead of formation of a cyst containing abundant mucinous materials. Mucinous adenocarcinoma, either primary or secondary, can be easily confirmed by clinical information and the presence of stromal invasion. Criteria to classify a tumor as urachal in origin are as follows: 1) presence of urachal remnants, 2) tumor growth in the bladder wall and 3) in the dome of urinary bladder, 4) absence of dysplastic intestinal metaplasia or dysplastic mucosal change, and 5) exclusion of other primary malignancies.14
We herein describe a rare case of mucinous tumor of uncertain malignant potential arising in the urachus. To the best of our knowledge, this is the first reported case in Korea and the fifth case in the English literature. We expect that this report will help to clarify the biological behavior and therapeutic implications of urachal mucinous tumors.