Ectopic kidney: pelvic kidney and crossed fused ectopia

What is an ectopic kidney?

While a baby grows in the womb, the kidneys start out in the pelvis and then slowly move up to their usual place in the back, near the ribs. Sometimes one kidney does not complete this move, or it crosses to the other side. A kidney that sits lower, higher or on the opposite side from its usual position is called an ectopic kidney.

The main types are:

• pelvic kidney: the kidney stays low in the pelvis, near the bladder,
• crossed ectopia: the kidney crosses to the other side of the spine,
• crossed fused ectopia: the kidney that crossed over joins the kidney on that side, so both kidneys are on the same side.

Some studies suggest that about 1 in 1,000 people has an ectopic kidney. In one study of children, more than half of ectopic kidneys were in the pelvis.

Symptoms

Most children with an ectopic kidney have no symptoms. That is why it is usually found on an ultrasound during pregnancy, or during tests done for another reason, such as a urinary tract infection or belly pain.

If complications develop, there may be:

• belly or lower back pain,
• fever and pain when peeing,
• blood in the urine,
• high blood pressure.

What can it come with?

In an ectopic kidney, urine sometimes drains more slowly than normal. This makes some problems more likely:

• hydronephrosis: widening of the renal pelvis, usually mild and temporary,
• vesicoureteral reflux: urine flowing back from the bladder toward the kidney,
• urinary tract infections,
• kidney stones.

Rarely, there is a narrowing where the renal pelvis joins the tube to the bladder (UPJ obstruction).

Tests

The first test is a kidney and bladder ultrasound. If a kidney is not in its usual place, the doctor looks for it in the pelvis or on the other side. Urine and blood tests check for infection and show how well the kidneys work.

Not every child needs more tests; they are chosen for each child:

• a voiding cystourethrogram (VCUG) to check for reflux,
• a DMSA scan to measure each kidney’s share of function and look at the kidney tissue,
• a MAG3 scan when there is dilation, to check urine drainage.

Treatment and follow-up

If an ectopic kidney causes no symptoms and no damage, no treatment is needed. Surgery is not done to move the kidney into place. In most children, overall kidney function stays normal.

Treatment targets the problem that develops: infections, stones and reflux are each treated in the usual way, and blocked urine drainage is corrected with surgery. Children rarely need such an operation.

A kidney in the pelvis, or one fused with the other kidney, can be injured more easily by a blow. If your child wants to play contact sports, talk to the doctor first.

When to see a doctor

If a child with an ectopic kidney has a fever, belly or lower back pain or blood in the urine, do not wait for the scheduled visit; see a doctor.