A calculus (plural calculi) is a stone (a concretion of material, usually mineral salts) that forms in an organ or duct of the body. Formation of calculi is known as lithiasis. Stones can cause a number of medical conditions.
Some common principles (below) apply to stones at any location, but for specifics see the particular stone type in question.
Calculi are not to be confused with gastroliths.
Types of lithiasis 
- Calculi in the renal system (kidneys, ureters, urinary bladder, urethra) can be of any one of several compositions, including mixed. Principal compositions include oxalate and urate.
- Calculi in the nasal passages (rhinoliths) are rare.
- Calculi in the gastrointestinal tract (enteroliths) can be enormous. Individual enteroliths weighting many pounds have been reported in horses.
- Salivary duct calculus
Calculi usually are asymptomatic, and large calculi may have required many years to grow to their large size.
- From an underlying abnormal excess of the mineral, e.g., with elevated levels of calcium (hypercalcaemia) that may cause kidney stones, dietary factors for gallstones.
- Local conditions at the site in question that promote their formation, e.g., local bacteria action (in kidney stones) or slower fluid flow rates, a possible explanation of the majority of salivary duct calculus occurring in the submandibular salivary gland.
- Enteroliths are a type of calculus found in the intestines of animals (mostly ruminants) and humans, and may be composed of inorganic or organic constituents.
- Bezoars are lumps of indigestible material in the stomach and/or intestines; most commonly, they consist of hair (in which case they are also known as hairballs). A bezoar may form the nidus of an enterolith.
In kidney stones, calcium oxalate is the most common mineral type (see Nephrolithiasis). Uric acid is the second most common mineral type, but an in vitro study showed uric acid stones and crystals can promote the formation of calcium oxalate stones.
Pathophysiology and symptoms 
Stones can cause disease by several mechanisms:
- Irritation of nearby tissues, causing pain, swelling, and inflammation
- Obstruction of an opening or duct, interfering with normal flow and disrupting the function of the organ in question
- Predisposition to infection (often due to disruption of normal flow)
A number of important medical conditions are caused by stones:
- Nephrolithiasis (kidney stones)
- Urolithiasis (urinary bladder stones)
- Can progress to bladder outlet obstruction
- Cholelithiasis (gallstones)
- Gastric calculi can cause colic, obstruction, torsion, and necrosis.
Diagnostic workup varies by the stone type, but in general:
- Clinical history and physical examination
- Imaging studies
- Factors contributing to stone formation (as in #Etiology) are often tested:
- Laboratory testing can give levels of relevant substances in blood or urine
- Some stones can be directly recovered (at surgery, or when they leave the body spontaneously) and sent to a laboratory for analysis of content
Modification of predisposing factors can sometimes slow or reverse stone formation. Treatment varies by stone type, but, in general:
- Surgery (lithotomy)
- Antibiotics and/or surgery for infections
- Extracorporeal shock wave lithotripsy (ESWL) for removal of calculi
- There was a high probability of intraoperative and postoperative surgical complication like infection or bleeding
- The physicians would not perform surgery as in ancient cultures they were two different professions
See also 
- Grases F., Sanchis P., Isern B., Perelló J., Costa-Bauzá A. (2007). "Uric Acid as Inducer of Calcium Oxalate Crystal Development". Scandinavian Journal of Urology and Nephrology 41 (1): 26–31. doi:10.1080/00365590600831571. PMID 17366099.
- Lock, Stephen etc. (2001). The Oxford Illustrated Companion to Medicine. USA: Oxford University Press. 836. ISBN 0-19-262950-6.
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- "The Little Treatise on the Medical Treatment of the Back and of Hemorrhoids" is a manuscript, from the 18th-century, in Arabic, which discusses the treatment of calculi