a 29-year - old female was referred to our hospital because of a intermittent occurrence of right flank pain for 1-week . the patient had neither a family nor personal medical history . aside from the flank pain , biochemistry and hematologic results were within normal limits . a computed tomography scan of the abdomen and pelvis revealed an ovoid cystic mass located just anterior to the dome of the urinary bladder with a partially calcified wall ( fig the patient underwent a radical excision of this mass including the attached portion of the urinary bladder and median umbilical ligament . at laparotomy , the mass originated from the dome of the urinary bladder without connection to the bladder cavity . there was no evidence of pseudomyxoma peritonei or tumors of other organs including ovary and appendix . the patient has been followed - up postoperatively with no evidence of recurrence for 11 months . grossly , a multilocular cystic mass with abundant mucoid materials , measuring 5.53.51 cm , was found , which was connected to a small cuff of urinary bladder wall and a segment of median umbilical ligament ( fig . the mass did not show any papillary or solid lesions and did not communicate with the urinary bladder lumen . histologically , the cyst was lined by a tall columnar epithelium with cellular crowding and stratification ( fig . cytologically , the lining columnar cells had abundant mucin in the cytoplasm and exhibited loss of polarity , nuclear pleomorphism , and hyperchromatism in dysplastic areas , but there were no mitotic figures . no stromal invasion of the tumor cells was observed , although mucin was extravasated into the cyst wall ( fig . the underlying stroma was composed of hyalinized connective tissue . on the basis of the proliferation of atypical mucinous cells and the absence of stromal invasion , its association with urachal remnant and location just anterior to the dome of urinary bladder confirmed the primary urachal origin of this tumor . 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 - 9 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.10,11 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 table 1 . 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 . 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.14,15 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 .
urachal mucinous tumor of uncertain malignant potential is very rare and is characterized by a multilocular cyst showing the proliferation of atypical mucin - secreting cells without stromal invasion . as in ovarian and 
 appendiceal borderline tumors , it represents a transitional stage of mucinous carcinogenesis in the urachus . 
 in addition , this tumor may recur locally and develop into pseudomyxoma peritonei . 
 due to its scarcity and diagnostic challenges , we report a mucinous tumor of uncertain malignant potential arising in the urachus .