Cystic change and neoplasia in isolated thyroid swellings.

During a 6-year prospective study of clinically isolated thyroid swellings (ITS), 148 (37 per cent) of 395 swellings were cystic as defined by the aspiration of fluid during fine needle aspiration cytology (FNAC). In the 106 (72 per cent) patients operated upon, 47 per cent of the cystic swellings were neoplastic and 14 per cent were malignant. In men 29 per cent of cystic swellings were malignant and 11 per cent in women. Only twelve cystic ITS were permanently abolished by aspiration and FNAC was inaccurate in predicting neoplasia. The incidence of malignancy in cystic ITS is higher than generally accepted and most cysts not abolished by aspiration should be removed.