Cyst

Cyst (kystis, 'a bladder'), a word sometimes used in the original sense as applied to hollow organs with thin walls, as the urinary bladder and gall-bladder; but commonly reserved for the designation of pathological structures or new formations within the body having the bladder form. Cysts may arise in two different ways: (1) either by the accumulation of products within cavities normally present, or (2) by the independent formation of a cavity. Of the first, wens, collections of secretion in a sebaceous gland of the skin, are the commonest example; instances of the second are cystic tumours of the Ovary (q.v.) and the sacs developed in connection with certain parasites ('bladder-worms;' see HYDATIDS, ENTOZOA). The structure of their walls is still more variable than their mode of origin; sometimes they are thin and transparent, sometimes dense and fibrous. They are either simple or compound, unilocular or multilocular; they are sometimes small, numerous, and separate; in other cases they grow to an enormous size, and are very complex. Some cysts are present at birth, and remain through life almost unchanged; some increase rapidly in size, and form large and dangerous tumours. For Cystic Worms, Cysticercus, see BLADDER-WORM, CESTOIDS, TAPEWORM.