Kidney stone, also known as kidney calculus or renal calculus, is a solid mass made of crystal-forming substances in the urinary system. Though all types of kidney stones originate in the kidneys, they may be found in the ureters, bladder and urethra.
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Many renal calculi of small sizes are formed and passed without causing symptoms. If the calculus is 3 mm or more, it may cause blockage of the ureter and associated renal colic pain.Types of kidney stones
There are several different types of kidney stones. Urolithiasis refers to all types of calculi originating anywhere in the urinary system. In relation to the type of their location, renal calculi are categorized as nephrolithiasis (kidney), ureterolithiasis (ureter) and cystolithiasis (bladder). Another type of classification pertains to the type of crystal forming minerals and organic compounds constituting these calculi.Renal calculi containing calcium
Most of the kidney stones are made of calcium compounds, especially calcium oxalate. Other calcium compounds are calcium phosphate in the form of calcium hydroxyphosphate (apatite), calcium phosphate carbonate (carbonate apatite) and brushite (CaHPO4·2H2O).Calcium oxalate kidney stones
The calcium oxalate uroliths exist in combined monohydrate and dihydrate forms.The calcium oxalate calculi formation is much dependent upon the type of diet taken. Low calcium diet can lead to increased oxalate absorption from the intestine and its increased excretion in the urine. The concentration of urine and availability of oxalate in the urine increase the risk of oxalate urolith formation. High intakes of dietary oxalates, high dietary sodium, low fluid intake, low potassium intake, low citrate intake and low magnesium intake are other risk factors for developing calcium oxalate kidney stones.
Calcium phosphate kidney stones
Calcium phosphate renal calculi have an underlying medical cause. These types of calculi are usually associated with systemic disorders like primary hyperparathyroidism, secondary hyperparathyroidism, renal tubular acidosis, hyperphosphaturia and hypercalciuria. The availability of calcium and PO43- in the urine helps in seeding of these types of uroliths. Urine dilution with sufficient intake of water and reducing sodium intake to reduce sodium and calcium excretion can help in reducing the risk factors and recurrence.Struvite kidney stones
Struvite type of renal calculi are mostly composed of struvite (magnesium ammonium phosphate). Struvite calculi also contain deposits of calcium carbonate-apatite. Infection in the upper urinary tract causes these types of uroliths. Struvite kidney stones can form only when the urine is alkaline and saturated levels of magnesium ammonium phosphate are present in urine. The urease-producing types of bacteria cause conversion of urea in the urine into carbon dioxide and ammonia by the catalytic action of the enzyme urease. Ammonia increases the pH of urine and also reacts with the magnesium and phosphate ions in the urine to form these types kidney struvite.Uric acid kidney stones
These types of calculi are associated with an excessive amount of uric acid in the urine (hyperuricosuria) with or without an excessive amount of uric acid in the serum (hyperuricemia). The major factors for the formation of uric acid uroliths are, chronic dehydration, low urine output, concentrated urine output, rich animal protein diet, excessively acidic urine, certain metabolic abnormalities, obesity and affliction by gout. Certain hereditary factors may also play a part in the formation of these types of kidney nephrolith. Uric acid and oxalate stones are common in patients with inflammatory bowel disease (Crohn's disease or ulcerative colitis) and in patients who had undergone colon resection.Cystine kidney stones
Individuals suffering from cystinuria, cystinosis and Fanconi syndrome develop these uroliths. Cystinuria is a hereditary disorder running in families. It causes the kidneys to excrete the amino acid cystine in the urine. Cystine calculus formation can be treated by alkalinizing urine and restricting dietary animal protein, especially red meat.Staghorn kidney stones
Struvite have the potential to grow into staghorn uroliths. Staghorn nephrolith are branched and occupy a large portion of the renal pelvis and one or more of calices. Cystine or uric acid calculi, either in pure form or mixed with other components may also grow into staghorn. These type of kidney stones, if not treated early and properly, have the great risk of causing, permanent kidney damage, renal failure and life threatening sepsis.Persons affected by xanthinuria often produce nephrolith composed of xanthine. In very rare cases, medications like indinavir, acyclovir, sulfadiazine and triamterene may get deposited as kidney stones.
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References: 1.http://kidney.niddk.nih.gov/kudiseases/pubs/stonesadults/ 2.http://www.kidney.org/atoz/content/diet.cfm 3.http://kidney.niddk.nih.gov/kudiseases/pubs/kidneystonediet/index.htm 4.Kristensen C, Parks JH, Lindheimer M, Coe FL. Reduced glomerular filtration rate and hypercalciuria in primary struvite nephrolithiasis. Kidney Int 1987; 32:749. 5.Viprakasit DP, Sawyer MD, Herrell SD, Miller NL. Changing composition of staghorn calculi. J Urol 2011; 186:2285. |
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