*2.3.13. Megacystis*

It represents an enlarged urinary bladder usually due to a bladder outlet obstruction [lower urinary tract obstruction (LUTO)], which may appear also in nonobstructive conditions (megacystis-microcolon-intestinal hypoperistalsis syndrome). It can be detected from the first trimester scan in about 1 in 1500 pregnancies [28].

Prognosis, management, prediction of resolution, and postnatal outcome depend on the subsequent cause. Fetal lower urinary tract obstruction (LUTO) has an incidence of 2.2/10000 births and it is usually diagnosed during the late first or early second trimester of pregnancy [28, 29]. The most common condition in the LUTO spectrum includes urethral valves, urethral atresia, and urethral stenosis.

#### *2.3.14. Posterior urethral valves*

It is a condition that causes lower urinary tract obstruction due to a membrane-like structure in the posterior urethra of male fetuses. The disease is usually sporadic, and has a heterogeneous embryologic origin. Young type I syndrome valves seem to result from an exaggerated development of the urethrovaginal folds with an abnormal insertion of the distal end of the Wolffian ducts. Other valves, like in Young type III, develop because of abnormal canalization of the urogenital membrane [30]. Distention of the bladder (megacystis) leads to vesicoureteral reflux and hydronephrosis and can cause renal dysplasia [30].

Posterior urethral valves can be associated with other anomalies of the urinary tract (sequence) megacystis, megaureter, hydronephrosis, paraureteral diverticula, and dilatation of proximal urethra, cryptorchidism, and hypospadias. There are also extraurinary anomalies that can be associated: tracheal hypoplasia, patent ductus arteriosus, total anomalous pulmonary vein drainage, mitral stenosis, scoliosis, skeletal anomalies in lower extremities, and imperforate anus. The most frequent chromosomal abnormalities that can be associated are: trisomies 18 and 13, del 2q, and 69 XXY.

Ultrasound diagnosis can be made in the presence of megacystis, hydroureter, and hydronephrosis in a male infant. In female fetus, lower urinary tract obstruction includes agenesis of the urethra, megacystis-microcolon-intestinal hypoperistalsis syndrome, and variants of the caudal regression syndrome. When the rupture of the megacystis intervenes, urine can extravasate into the peritoneal cavity. Oligohydramnios can also occur.

The differential diagnosis is difficult in prenatal life, and includes ureteropelvic junction obstruction, ureterovesical junction obstruction, primary megaureter, and massive vesicoureteral reflux, absence of the urethra or detrusor hypertrophy.

Prognosis depends on the renal reserve, which can be difficult to assess prenatally. Another factor that can influence the outcome is the timing of the occurrence of urinary obstruction, and this is a critical factor: the earlier its appearance–the worse the prognosis. Complications include: pneumomediastinum and pneumothorax, related to pulmonary hypoplasia, associated congenital anomalies, renal failure, and surgical complications after decompressive surgery. Termination of pregnancy can be offered if the prognosis is poor and if other anomalies are associated. In utero vesicoamniotic shunts are possible, but the results at 2 years of life are not very encouraging [31].
