Calculus disease of the urinary tract encompasses calcifications and calculi of the kidneys, ureters, bladder, and urethra. Urolithiasis refers to the presence of stones within the lumen. This term includes calculi that form within a cavity that communicates with the collecting system, such as a calyceal diverticulum or bladder diverticulum. Subcategorization of calculous disease based on location within the urinary tract is often clinically useful. The term nephrolithiasis refers to calculi within the pelvicaliceal system. Nephrocalcinosis indicates the presence of intraparenchymal renal calcifications-cortical, medullary, or mixed. Medullary nephrocalcinosis can lead to urolithiasis by way of erosion of a stone into a calyx. The parenchymal calcification of nephrocalcinosis is usually metastatic, that is, calcification of otherwise normal renal tissue due to abnormally high levels of urinary or blood calcium. An additional category of urinary tract calcification is dystrophic calcification of abnormal tissue, which can occur with an inflammatory process, neoplasm, or renal cystic disease.
Approximately 90% of nephrocalcinosis in children involves the tubules, tubular epithelium, and adjacent interstitial tissue, that is, medullary nephrocalcinosis. The most common causes of medullary nephrocalcinosis in children are metabolic conditions that lead to hypercalcemia and/or hypercalciuria. Type 1 renal tubular acidosis is the most common metabolic condition to induce nephrocalcinosis in children. Other potential causes include hyperparathyroidism, Cushing syndrome, milk-alkali syndrome, hypervitaminosis D, prolonged immobilization, skeletal metastatic disease, loop diuretic therapy (infants), corticosteroid administration, idiopathic hypercalciuria, Williams syndrome, medullary sponge kidney, obstructive uropathy, tyrosinemia, Fanconi syndrome, autosomal recessive polycystic kidney disease, hyperoxaluria, and hyperuricosuria. Potential sequelae of nephrocalcinosis include passage of calculi into the collecting system, renal colic, hematuria, and urinary tract infection.
Nephrocalcinosis in premature infants most often involves the medullary portions of the kidneys. The etiology of stone formation in these infants is likely multifactorial. Immaturity of the kidneys apparently plays a role, as glomerular and tubular function is subnormal in preterm infants. Parenteral nutrition results in elevated urinary oxalate. The use of loop diuretics such as furosemide is an important predisposing factor for stone formation in neonates. Loop diuretics impair the reabsorption of magnesium and calcium, resulting in a variable degree of hypercalciuria. There is an inverse relationship between the prevalence of nephrocalcinosis in neonates undergoing furosemide therapy and the gestational age and birth weight. The earliest manifestations of stone formation in these patients develop approximately 30 days after the initiation of diuretic therapy. Spontaneous resolution occurs in most, but not all, of these infants within several months after cessation of furosemide use. Nephrocalcinosis has also been reported in association with the administration of aminoglycosides and dexamethasone.1,2
Cortical nephrocalcinosis occurs within the peripheral aspects of the kidneys and the central septa of Bertin. Common causes of cortical nephrocalcinosis in children are acute cortical necrosis, chronic glomerulonephritis, and oxalosis. Other potential causes include Alport syndrome (hereditary nephritis), renal transplant rejection, hyperoxaluria, ethylene glycol poisoning, and AIDS-associated infections (e.g., ...