Prenatal diagnosis of congenital patent urachus and allantoic cyst: the value of color flow imaging.

Cystic lesions of the umbilical cord are now increasingly detected prenatally using high resolution ultrasonography; differential diagnoses include allantoic cyst,l-3 vitelline or omphalomesenteric duct cyst,4 local degeneration or focal edema of Wharton's jelly (pseudocyst),M hematoma? and focal dilatation of umbilical vessels.B,9 Of these, the accurate diagnosis of allantoic cyst is of critical importance as this condition may be associated with omphalocele,2 urinary tract obstruction,3 and urachal anomalies)0-13 In this report we describe two cases of patent urachus diagnosed prenatally by ultrasonography in which the most prominent prenatal finding was the presence of a large umbilical cord cystic mass. In one of these cases the adjunctive use of color flow imaging allowed the identification of a characteristic feature that proved to be helpful in establishing a confident prenatal diagnosis of allantoic cyst.