Prenatal sonographic findings in bladder exstrophy.

Obstetric sonography routinely images both the normal and malformed fetal genitourinary tract.•-• The fetal kidneys and bladder are commonly identified beginning at 15 weeks menstrual age, and 90% of fetal kidneys can be visualized by 20 menstrual weeks. The fetal bladder can be localized by the umbilical arteries that always travel along its lateral margin (Fig. 1). Therefore, even when completely empty, the umbilical artery position marks the fetal bladder position when the bladder lies in its normal anatomic location. When the bladder distends, the arteries are pushed aside. The fetal bladder normally fills and empties every 50 to 155 minutes.6 After complete emptying, the fetal bladder may not be visualized for short periods of time; however, prolonged or serial observation should allow identification of the bladder in the normal fetus. Further, the cyclical change in bladder volume over time helps to differentiate it from other potential cystic lesions in the pelvis. When the fetal kidneys are absent the urinary bladder is nonvisualized, reflecting absent fetal urine production, and concomitantly there is associated severe oligohydramnios. Nonvisualization of the urinary bladder is also encountered in some cases of severe renal dysplasia, but is again associated with severe oligohydramnios. Alternatively, when normal fetal kidneys are identified one expects to identify the fetal bladder within the pelvis. We report a case of bladder exstrophy in which the only prospective ultrasound observation was absence of the fetal bladder. In retrospect, there is also noted to be a caudal insertion of the fetal umbilical cord into the lower abdomen. A previous report of prenatal diagnosis of bladder exstrophy identified a ventral solid mass protruding from the fetal abdomen associated with inability to visualize a normal bladder. 7