[Heterotopic (extraosseous) calcification (calcinosis). Etiology, pathogenesis and clinical importance].

Heterotopic tissue calcification represents a pathological event which goes along with active extra- and intracellular metabolic processes. The heterotopic calcification is not the manifestation of tissue ageing. Aetiologically, metastatic calcification, dystrophic calcification and genetic-hereditary calcification are distinguished. Two pathogenetic mechanisms play a role during the heterotopic calcification. The intracellular calcification is based upon the function of mitochondria as regulator of the calcium concentration and as "lime-catcher". The extracellular calcification is initiated by membraneous organelles--so-called matrix vesicles. The further steps are the production of hydroxylapatite crystals which are eliminated from the matrix vesicles in the extracellular spaces. Special types of heterotopic calcification are hypercalcaemias (tumour-associated hypercalcaemias, primary and tertiary hyperparathyroidism, drug-induced hypercalcaemias), tumoral calcinosis, intratumoral calcifications, calcifications of different organs (lung, heart, vessels, joints, ligaments, skin or kidney). Some calcifications of organs show partly overlapping aetiological factors and pathogenetic mechanisms.