Antenatal Hydronephrosis

Antenatal (before birth) hydronephrosis (fluid filled enlargement of the kidney) is detected in the fetus by ultrasound studies performed as early as the first trimester of pregnancy. In most instances this diagnosis will not change obstetric care, but will require surveillance and possible surgery during infancy and childhood.

Usual causes of antenatal hydronephrosis:

Blockage This may occur at the kidney in the ureteropelvic junction (UPJ), at the bladder in the ureterovesical junction, or in the urethra (posterior urethral valves). Blockages usually have to be corrected.

Reflux Vesicoureteral reflux occurs when the valve between the bladder and the ureter is incompetent permitting urine to backflow to the kidney when the bladder fills or empties. Most children (75%) outgrow this during childhood but need surveillance and antibiotic prophylaxis to try to prevent kidney damage before they outgrow the reflux. Only a minority of refluxers require surgical correction either because of failure to outgrow reflux or because of breakthrough urinary tract infections.

Duplications, etc. Perhaps 1% of all humans have two collecting tubes from a kidney. These may show up on fetal ultrasound. Occasionally patients with duplication have a ureterocele which is a balloon-like obstruction at the end of one of the duplex tubes.

Multicystic kidney is a non-functional cystic kidney.

Management During Pregnancy

In nearly all instances of antenatal hydronephrosis, ultrasound surveillance is all that is necessary. In the rare fetus with severe obstruction of both kidneys and insufficient amniotic fluid, drainage of the kidneys or bladder by tube or operation has been performed experimentally. While these procedures are technically possible, the outcome of the babies has not, to date, been improved. These babies are likely to have very abnormal kidneys that do not function well and also may have inadequate lung development. For most cases of antenatal hydronephrosis pregnancy is not affected and delivery can be performed normally. Very huge obstructed kidneys may require C-section delivery, but this is unusual.

Management After Birth

Postnatal ultrasound is usually performed on the third day of life. If hydronephrosis persists we must rule out reflux with a voiding cystourethrogram (this requires a catheter in the bladder and we usually use antibiotic prophylaxis) and obstruction with a diuretic renal scan (requiring an IV and a catheter). The renal scan is more accurate if delayed until the baby is one month old. Most refluxers are managed by antibiotics and surveillance with periodic ultrasounds and voiding cystograms. Most blockages require surgical correction. In some babies the evidence for obstruction is marginal or the degree of blockage is mild. In these babies the tests might be repeated after a few months. After all testing is done, some babies have hydronephrosis without reflux or obstruction. We usually follow these patients with periodic ultrasounds to monitor the hydronephrosis and the growth of the kidneys. A multicystic kidney doesn't work, but the opposite kidney is usually normal. There is controversy whether a multicystic kidney should be removed or left alone. Unless it is causing a problem with breathing or eating - and unless there is a question of tumor or blockage - we usually leave these alone in infancy and do a follow-up ultrasound at 6 months and a year. If the multicystic kidney is still large we recommend removal.