Hydronephrosis: A Defense Mechanism for the Kidneys

What Is Hydronephrosis?

In general terms, hydronephrosis is a radiology term describing fluid buildup within the kidney. The kidneys filter toxins and excess fluid from the blood in order to produce urine. Ordinarily, urine is excreted from the kidney down the urine tube (ureter) and into the bladder.

Under normal circumstances, the urine leaves the kidney on a regular basis. However, if something (such as a narrowing of the ureter, backflow of the urine, or a kidney stone) causes a delay in the discharge of urine from the kidney, then the kidney can become more swollen with fluid than normal.

In many cases, hydronephrosis occurs in normally-functioning kidneys but some cases are associated with abnormal or poorly-functioning kidneys or other genetic conditions.

How Is hydronephrosis Diagnosed?

Most pregnant women will undergo an ultrasound about halfway (20 weeks) into their pregnancy and, in some instances, hydronephrosis in the fetus can be seen at that time. Hydronephrosis in these cases can be on one or both sides and can be associated with swelling of the ureter(s) or bladder. If this occurs, additional ultrasounds are done during the pregnancy in order to keep track of any changes. In younger babies after birth, hydronephrosis, even when severe, often does not cause any noticeable symptoms.

In other cases, babies or children might develop symptoms such as a urinary tract infection, blood in the urine, excessive fussiness, unexplained flank or abdominal pain, nausea or vomiting for which their doctor may order an abdominal or kidney/bladder ultrasound or occasionally a CT scan which will detect kidney swelling.

The greater the degree of hydronephrosis, the more likely that the child will have symptoms. Some patients with significant hydronephrosis may not have symptoms, especially if the swelling happened gradually over time.

Why Does the Kidney Swell in These Cases?

Hydronephrosis is like a defense mechanism for the kidney when urine is slow to drain. The stretching of the kidney allows the backpressure of urine to be more evenly distributed. This may help to limit or slow down some of the potential damage to the kidney from urine backing up abnormally. 

Can Hydronephrosis Get Better on Its Own?

Yes! Younger children with milder forms of swelling who are not having symptoms can often maintain kidney function. The primary care doctor or a pediatric kidney specialist, like a nephrologist or urologist, can monitor the degree of swelling by obtaining a kidney ultrasound every few months as they see fit.

In many cases, but not all, the hydronephrosis may improve as its cause improves, especially in young babies as they grow over time. Additional testing such as a cystogram (bladder catheter study to look for abnormal urine reflux from the bladder into the ureter) or a nuclear medicine renal scan (to assess kidney function and drainage) may be needed along with ultrasounds to help determine the course of the hydronephrosis.  

When Do Children with Hydronephrosis Need Surgery?

Hydronephrosis can cause various symptoms like flank pain or vomiting or can be detrimental to the health of the kidney over time. Doctors must determine the cause of the swelling and whether it is something that may improve on its own. If it appears to be worsening, a corrective procedure may be necessary.

For example, kidney stones that become lodged in the ureter as they try to pass can cause temporary blockage of the urine flow and hydronephrosis in previously healthy patients. Some stones may pass on their own with medication and increased fluid intake and the hydronephrosis will get better when this happens. When a stone becomes stuck or causes too much pain, surgery to break up and remove it may be necessary.

In other cases, congenital or acquired blockage may require surgery. Indirect causes of hydronephrosis such as urine reflux or an abnormally positioned ureter may require surgery if the problem persists over time and causes the kidney swelling to worsen or cause symptoms.

Each case of hydronephrosis is unique and a decision to do surgery is not taken lightly. The exact cause of the issue must be determined before recommending a course of action. This may not be apparent at first and may require several imaging studies to follow the course of the diagnosis in question.