Calculus (medicine)

A calculus (: calculi), often called a stone, is a concretion of material, usually mineral salts, that forms in an organ or duct of the body. Formation of calculi is known as lithiasis (,/l//ɪ/'/θ//aɪ//ə//s//ᵻ//s/). 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.

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.

The word comes from Latin calculus "small stone", from calx "limestone, lime", probably related to Greek χάλιξ chalix "small stone, pebble, rubble", which many trace to a Proto Indo European language root for "split, break up". Calculus was a term used for various kinds of stones. In the 18th century it came to be used for accidental or incidental mineral buildups in human and animal bodies, like kidney stones and minerals on teeth.