Urinary Stones

In industrialized countries, urolithiasis is rare in children. When present, it is often associated with specific metabolic disorders or anatomic abnormalities. When patients under the age of 20 form stones, they usually do so in a recurrent fashion and require a thorough medical and surgical evaluation to develop a treatment plan that will prevent further stone formation.

Fundamental to the formation of a stone within the urinary tract is precipitation of crystals at the site where they are incorporated into the stone, usually the kidney. For precipitation of crystals in urine to occur, the urine must be "supersaturated" for the precipitating crystal. To understand supersaturation we will make an illustration with sugar and water with sugar being the precipitating crystal. When you initially stir water with a small amount of sugar added, the sugar completely dissolves. As you add more sugar, it takes longer to dissolve until a certain point where no matter how hard you stir the water the sugar crystals will not completely dissolve and forms a sediment at the bottom of the glass. This is supersaturation and how with some simplicity, stones develop.

The key features of the patient's history relevant to the formation of stones include family history, age of onset, fluid intake pattern, diet, medications, and history of infections. Certain stone formation has a genetic predisposition some following an autosomal recessive pattern, including cystinuria and primary hyperoxaluria, where some have an autosomal dominant pattern such as renal tubular acidosis (RTA) or the syndrome of idiopathic calcium oxalate urolithiasis. Stones that form in very young children often suggest primary hyperoxaluria or other enzymatic defects. Cystinuria, idiopathic calcium oxalate urolithiasis and primary hyperparathyroidism more often begin around puberty or in the mid-teens. Stone formation secondary to infection and/or obstruction related to a congenital malformation of the urinary tract often present before the age of 5. In some cases, extended immobilization, secondary to an injury that the child may have had with active growing bones can lead to moderate elevation in serum calcium with associated elevation in urinary calcium and stone formation within the urinary tract. Low fluid intake and unusual dietary patterns may bring out a tendency to stone formation in a patient with an underlying idiopathic calcium oxalate urolithiasis.

Most children or adolescents with urinary stones will present with either pain in their flank or abdominal region with associated blood seen in their urine, either microscopically or grossly. The appropriate work-up in that setting is to obtain an abdominal x-ray known as a KUB, as well as a renal and bladder ultrasound. If a stone is identified on either or both of the studies, there will be consideration for obtaining an IVU, or intra-venous urogram to distinctly define the location of the stone as well as degree of obstruction or blockage that it is causing.

In all children or adolescents with stone disease a thorough laboratory evaluation is required, including a urinalysis and urine culture as well as urine collected for calcium, oxalate, uric acid, citrate, cysteine, magnesium, and phosphate. A vast majority of stones will contain elements of calcium within them and therefore are easily seen on x-ray having the same density as bone. Depending on the size, number, and the location of the stone(s) as well as it's composition guides initial and then further management.

Some stones will have the potential to pass spontaneously if given time with appropriate hydration and pain control. However, for those stones that do not pass spontaneously, various interventions may be indicated. At our institution, we have treated patients with active stone disease from ages 3 years up through late adolescence. Whenever possible, we use the least invasive measures necessary to extract the stone. A great number of the patients that present with stone disease, have their stones present in the kidney and are amenable to undergoing ESWL (Extra Corporeal Shock Wave Lithotripsy). This has been shown to be effective in many centers across the country as well as ours. Often this is an outpatient procedure and the patient is usually comfortable within a day or so. This therapy is without incisions or scopes and focuses a beam of energy to a focal point, the location of the stone. During this therapy, the stone becomes pulverized into small particles or stone dust. Follow up studies have shown that the renal growth appears normal after such therapy and that there is no drop in renal function. On occasion, we need to leave an indwelling tube, called a ureteral stent due to a high quantity of stone fragments, as these may cause some obstruction further down the ureter as they work their way into the bladder. If the stone is lodged in the distal ureter and not amenable to ESWL therapy, cystoscopy with ureteroscopy or placing a scope into the ureter with direct visualization of the stone and stone removal may also been successfully performed. In these manipulations, it is often standard to leave an indwelling tube or ureteral stent for approximately three to four weeks. Bladder stones if they do occur often can be extracted through a scope or through a small, approximately 3 inch, incision on the lower abdominal wall. Once the removed stone has been sent for analysis and the blood tests and urine tests have been collected, dietary and medical management will proceed as well as close follow up to prevent stone recurrence. With aggressive follow up and management, we have been able to keep most of our patients from having recurring stone disease and symptoms.

Concerning complex stone cases, including staghorn calculi and calyceal diverticulum with calculi in them, we have successfully performed percutaneous nephrolithotomies which involves placing a scope through the flank or back region, directly into the kidney with extraction of the stone through the scopes. Occasionally, open surgery is required for certain complex stone removals. Presently we are following approximately 35 patients who have been seen and/or treated with stone disease here at Children's Hospital of Michigan who are now in a "metabolically" inactive state which is where we would like to have all patients.