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# Antenatal Hydronephrosis

The anomalous development of the urinary tract can be recognized in utero, thereby prompting and permitting the evaluation of congenital uropathies prior to the onset of complications or symptomatology. The widespread use of screening maternal and fetal ultrasonography (US) has understandably revolutionized the specialty of pediatric urology. Congenital uropathies are discovered in approximately 0.5% of screening maternal-fetal US examinations. Serial studies are indicated after discovering antenatal Hydronephrosis in order to assess progression or resolution. Furthermore, extra urinary anomalies must be sought as the incidence of compounding anomalies approaches 55%. Such a practice helps to establish perspective and facilitates counseling of the expectant parents. The most common urologic diagnoses include: Hydronephrosis, posterior urethral valves, duplex kidneys, multicystic dysplasia, prune belly syndrome, autosomal recessive polycystic kidney disease, Potter’s syndrome, and renal agenesis. Classic and cloacal exstrophies, cloacal anomalies and imperforate anus, neuroblastoma & mesoblastic nephroma can also be detected.

Hydronephrosis is overwhelmingly the most common finding and may be physiologic and non-obstructive or it may be secondary to obstruction at the ureteropelvic or ureterovesical junctions, vesicoureteral reflux, ureteroceles, duplications or bladder outlet obstruction. It is our job to distinguish between obstructive and non-obstructive processes. The widespread use of maternal/fetal US has created an epidemic of asymptomatic infants in whom this clinical question must be answered.

obstruction at the end of a ureter inside of the bladder. Vesicoureteral reflux is a condition in which the urine goes backward from the bladder up to the kidney. Posterior urethral valves are leaflets of tissue or membranous folds within the posterior urethra in males which cause bladder outlet obstruction. A multicystic kidney is a nonfunctional cystic kidney.

#### Testing

Ultrasonography, voiding cystourethrography (VCUG), intravenous pyelography (IVP), and diuretic renography (DR)/renal scan, are used in various combinations to evaluate the nature of the dilated upper urinary tract. Renal scans, more than any other imaging technique, have been widely promoted as the test of choice. Despite an extensive literature espousing the advantages of one imaging modality over another, insufficient data exists regarding the evaluation of upper urinary tract dilatation in infants and young children, such that a gold standard remains elusive. A thorough background in the embryology and anatomy of the urinary tract, and a clear understanding of transitional nephrology, are necessary to

#### Terminology

Hydronephrosis is an enlargement of the collecting system of the kidney. Hydroureteronephrosis includes the dilation of the ureter as well. The ureter is the tube that connects the kidney to the bladder. Obstruction is the restriction to urinary outflow that prevents normal renal (kidney) development or results in renal injury. The renal pelvis is a single hollow structure forming a cone-like transition from the kidney to the upper ureter area. Urine is initially collected in this area. Ureteropelvic junction (UPJ) is the site where the renal pelvis connects to the ureter. Ureterovesical junction (UVJ) is the site where the ureter connects to the bladder. A Duplication is two collecting systems from one kidney. Ureterocele is a ballon-like

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