Concept
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 (ˌlɪˈθaɪəsᵻs). 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. Calculi in the urinary system are called urinary calculi and include kidney stones (also called renal calculi or nephroliths) and bladder stones (also called vesical calculi or cystoliths). They can have any of several compositions, including mixed. Principal compositions include oxalate and urate. Calculi of the gallbladder and bile ducts are called gallstones and are primarily developed from bile salts and cholesterol derivatives. Calculi in the nasal passages (rhinoliths) are rare. Calculi in the gastrointestinal tract (enteroliths) can be enormous. Individual enteroliths weighing many pounds have been reported in horses. Calculi in the stomach are called gastric calculi (Not to be confused with gastroliths which are exogenous in nature). Calculi in the salivary glands are called salivary calculi (sialoliths). Calculi in the tonsils are called tonsillar calculi (tonsilloliths). Calculi in the veins are called venous calculi (phleboliths). Calculi in the skin, such as in sweat glands, are not common but occasionally occur. Calculi in the navel are called omphaloliths. Calculi are usually 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.
