Non- visualized Fetal Urinary Bladder
· Evacuated bladder- The bladder is usually readily visible, but prior to 16 weeks it may be empty for quite long periods. The fetal bladder normally empties every 30—45 minutes. During the course of an ultrasound study the bladder size may increase, or voiding may be observed as the urine streams into the amniotic fluid.
· Bilateral renal agenesis- Bilateral renal agenesis (Potter’s syndrome) has an incidence of 1 in 3000—4000. It is incompatible with life and most affected infants die within a few hours of birth because of pulmonary hypoplasia caused by OH. Low set ears, hypertelorism, beak nose and limb deformity may occur as a result of OH.
· Bilateral severe renal dysplasia- The majority of cases of multicystic renal dysplasia are unilateral, but when bilateral the condition is fatal, with OH and pulmonary hypoplasia.
· Bilateral severe renal hypoplasia- Renal hypoplasia may be unilateral or bilateral and the small kidney may be difficult to locate. The contralateral kidney may be hypertrophied, but if it is small then there may be OH. Renal hypoplasia may also be associated with other anomalies.
· Bladder extrophy- This is a rare malformation occuring once in 50 000 births. The bladder is exposed on the abdominal wall and there is diastasis of the symphysis pubis. If the mucosa of the posterior bladder wall protrudes through the abdominal defect it may cause a prominence on the abdominal wall. Free communication between the bladder and amniotic cavity prevents bladder distension.
· Bilateral PUJ obstruction- Approximately 10—30% of PUJ obstructions are bilateral but involvement is usually asymmetric and severe bilateral obstruction is rare. When bilateral PUJ obstruction is severe there will be OH, which may cause pulmonary hypoplasia. Paradoxically PH may also occur in up to 25% of cases.
· Unilateral PUJ with contralateral renal agenesis/dysplastic kidney- Rarely unilateral PUJ obstruction may be associated with contralateral renal agenesis or multicystic dysplastic kidney, both of which increase the significance of the PUJ obstruction.
· Evisceration of bladder in gastroschisis- With larger anterior abdominal wall defects, the stomach as well as the urinary bladder (and in the female fetus the adnexae) may be extruded into the amniotic cavity. The characteristic sonographic feature of gastroschisis is the observation of free loops of bowel floating in the amniotic fluid as early as 14 weeks of gestation.
· Herniation of urinary bladder in LBWC- The limb—body wall complex is a severe malformation with multiple system anomalies. The lateral body wall defect may involve the thorax, the abdomen or both. There is visceral evisceration through the fetal trunk defects. The eviscerated organs form a complex mass, with the individual organs non-recognizable.