Struvite (triple phosphate) - usually opaque but variable Plain radiographĬalcium-containing stones are radiopaque: The much greater sensitivity of CT to tissue attenuation means that some stones radiolucent on plain radiography are nonetheless radiopaque on CT. These depend on the stone composition and vary according to modality. with other stones which are crystalline with only a minor organic element) 15 Mostly (~65%) made of organic proteins, carbohydrates, and glucosamines (cf. Guaifenesin/ephedrine stones which are radiolucent Triamterene stones which are poorly radiopaque Sulphonamides stones which are radiolucent Magnesium trisilicate stones which are poorly radiopaqueĬiprofloxacin stones which are radiolucent The formation of renal tract stones has since been described with other members of the protease inhibitor class Indinavir is a protease inhibitor, a class of antiretroviral drugs used in HIV treatment Indinavir stones are typically radiolucent (see case 13) Cystine stonesĬystine stones are also formed in acidic urine and are seen in patients with congenital cystinuria. Hyperuricosuria is not always associated with hyperuricemia and is seen in a variety of settings (see above), although in most instances uric acid stones occur in patients with no identifiable underlying etiology 6. Uric acid crystals form and remain insoluble at acidic urinary pH (below 5). Uric acid and cystine are also found as minor components. The struvite accounts for ~70% of these calculi and is usually mixed with calcium phosphate thus rendering them radiopaque. They can grow very large and form a cast of the renal pelvis and calyces resulting in so-called staghorn calculi. Proteus, Klebsiella, Pseudomonas, and Enterobacter), resulting in hydrolysis of urea into ammonium and increase in the urinary pH 6,10. Struvite (magnesium ammonium phosphate or "triple phosphate") stones are usually seen in the setting of infection with urease-producing bacteria (e.g. Rarely the underlying cause is primary oxaluria, a liver enzyme deficiency leading to massive cortical and medullary nephrocalcinosis, and renal failure.Ĭertain medications 14 can predispose to calcium oxalate or calcium phosphate calculi, including: Interestingly hyperuricosuria is also associated with increased calcium-containing stone formation and is thought to be related to the uric acid crystals acting as a nidus on which calcium oxalate and calcium phosphate can precipitate 6. In most instances, no specific cause can be identified, although most patients have idiopathic hypercalciuria without hypercalcemia.īrushite is a unique form of calcium phosphate stones that tends to recur quickly if patients are not treated aggressively with stone prevention measures and are resistant to treatment with shock wave lithotripsy. Most renal calculi contain calcium, usually in the form of calcium oxalate (CaC 2O 4) and often mixed with calcium phosphate (CaPO 4) 1,6. Crohn disease) resulting in fats binding calcium Low gut absorption of calcium, leading to increased absorption of oxalate Hypercalciuria: most common metabolic abnormality Urease hydrolyzes urea to ammonium thus increasing urinary pH The more common composition of stones include (more detail below):Ĭalcium oxalate +/- calcium phosphate: ~75%Ĭertain risk factors have been identified including 8:Įspecially with urease producing bacteria (see below) The composition of urinary tract stones varies widely depending upon metabolic alterations, geography, and presence of infection, and their size varies from gravel to staghorn calculi. In children, vague abdominal pain is more typical than the classic colicky pain described by adults 26. Some patients may also present with the complication of obstructive pyelonephritis, and may, therefore, have a septic clinical presentation. Hematuria, although common, may be absent in approximately 15% of patients 1. Small stones that arise in the kidney are more likely to pass into the ureter where they may result in renal colic. Clinical presentationĪlthough some renal stones remain asymptomatic, most will result in pain. Urolithiasis can also occur in children and infants, with an even sex distribution, or slight female predilection 24,25. struvite stones are more frequently encountered in women, like urinary tract infection as more common) 8. By far the most common stone is calcium oxalate, however, the exact distribution of stones depends on the population and associated metabolic abnormalities (e.g. The lifetime incidence of renal stones is high, seen in as many as 5% of women and 12% of males. Most patients tend to present between 30-60 years of age 1.
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