They are, however, readily apparent on noncontrast CT. Radiographic imaging can be difficult because pure uric acid calculi typically are radiolucent. Excess ingestion of animal meat protein (i.e., meat of all types, including poultry) can be detected by measuring urinary sulfate levels. 23 In general, these patients excrete excessive uric acid (although some have normouricosuria) and have low urinary pH and urine volumes. Men with gout have a twofold risk of having a uric acid calculus. Other predisposing conditions include gout, insulin-resistant states, and end-ileostomies. The primary cause of uric acid stones is a urinary pH below the p K a for uric acid (5.5). 22 Uric acid is a by-product of ingested or endogenous purine metabolism and is excreted in the urine primarily in insoluble form. Uric acid stones may consist of uric acid only, or they also may contain calcium. Idiopathic renal tubular acidosis (types 1, 2, and 4) Hypocitraturia (less than 450 mg per 24 hours ) Potassium citrate†, allopurinol (Zyloprim 100 to 300 mg daily, given orally) Increased uric acid promotes calcium oxalate crystallization via the formation of nuclei Hyperuricosuria (more than 800 mg per 24 hours ) Metabolic error with high level of oxalate production and urinary excretion Malabsorption from any cause with increased urinary oxalate to complex with calciumĭecrease oxalate intake, increase calcium intake Hyperoxaluria (more than 45 mg per 24 hours ) Increased bone demineralization or increased intestinal calcium absorption Thiazide diuretic*, potassium citrate (Urocit-K)† Increased intestinal absorption of calcium Hypercalciuria (more than 250 mg per 24 hours ) 17 Calcium oxalate calculi not associated with an obvious laboratory abnormality can be treated empirically with oral potassium citrate (Urocit-K, 30 to 60 mEq per day) or sodium citrate (Bicitra) to increase urine pH and levels of urinary citrate. Additionally, decreasing the intake of oxalates contained in foods such as spinach, rhubarb, beets, chocolate, nuts, tea, strawberries, soy foods, and wheat bran may be beneficial. Note that there are no specific medications for hyperoxaluria medical treatment consists of increasing calcium intake (particularly with meals) to control enteric hyperoxaluria. Treatments for these stones depend on the underlying condition ( Table 4). Other causes of calcium oxalate stones include hyperoxaluria (i.e., more than 45 mg per 24 hours ) and hyperuricosuria (i.e., more than 800 mg per 24 hours ). The cause of hypocitraturia often is idiopathic, although high dietary acid loads (e.g., from excessive meat intake) and dehydration can exacerbate this condition. Hypercalciuria (i.e., more than 250 mg per 24 hours ) is the most common metabolic abnormality associated with these calculi, followed by hypocitraturia (i.e., less than 450 mg per 24 hours ), which involves a deficiency of the naturally occurring stone inhibitor citrate.

The causes of calcium oxalate stones and their mechanisms are listed in Table 4. May demonstrate dilation of collecting system. Calculi may appear as filling defect.Ĭonventional MRI is not useful for imaging calculi.Ĭalculi appear as hyperechoic lesions that cast acoustic shadows. Delay in contrast excretion if obstruction is present. Evaluates renal parenchyma, hydronephrotic changes, and surrounding organs for other etiologies of abdominal pain.Ĭalculi visible on scout film. Urinary calculi larger than 2 mm may be visible. Microscopic or gross hematuria acidic urine alkaline urine (with struvite calculi) pyuria crystals from involved calculiĮlevated urinary calcium, oxalate, and sodium levels decreased urinary volume and citrate levelsĪbdominal, kidney, and upper bladder radiography UTI, interstitial cystitis, prostatitis, urinary calculi, peritonitisĮlevation in creatinine levels with obstructing calculi hypokalemia and hyperchloremia with renal tubular acidosis elevated serum calcium levels with parathyroid disease

Ureteral calculi, urethritis, prostatitis Ureteral calculi, hernia, testicular mass Urinary calculi, musculoskeletal inflammation, pyelonephritis Small renal calculi, nonurologic etiology (gastrointestinal origin)įlank pain (sharp, extreme pain with sudden onset) Nonspecific findings of shock (including possible sepsis) Urinary calculi, urothelial tumor, UTI, BPH, renal mass UTI, urinary calculi, interstitial cystitis Obstructing urinary calculi, bowel disease

Staghorn calculi