febrile [fe-brile] Relating to or affected by fever (a 'temperature').

fever A rise in body temperature above the normal (37°C). It is usually caused by a viral or bacterial infection.

fibre optics The use of long, flexible fibres, usually made of very fine clear glass or plastic, to transmit light and images. Techniques involving fibre optics are often used to look at structures inside the body that would otherwise be inaccessible without surgery: see endoscope .

fibroadenoma [fi-bro ad-e-no-ma] A solid, benign lump (not a cancer ) made up of fibrous and glandular tissue. Many breast lumps found in younger women are fibroadenomas.

fibrocystic breast disease [fi-bro cys-tic] see benign fibrocystic changes .

fibroid [fi-broid] A benign growth that may develop in the wall of the uterus . Fibroids are common, especially in women over fifty. Some become very large, and may cause bleeding and pain, though they usually shrink after menopause. They do not need to be removed unless they are causing problems. Also called fibroid tumour, uterine fibroma , fibromyoma.

fibroma [fi-bro-ma] A benign tumour (not a cancer ) that forms in connective tissue.

fibrosarcoma [fi-bro sar-co-ma] A malignant tumour (a cancer ) that starts in connective tissue. Fibrosarcomas are found in people of all ages; they may be congenital . They occur most commonly in the leg, though they may be in any organ . Fibrosarcomas in soft tissue have a considerably better outlook(prognosis ) than those starting in bone.

fistula [fis-tu-la] An unwanted hole or opening between two hollow parts of the body such as the intestine and the stomach , or between a hollow organ and the outside, for example, a hole in the skin . A fistula can be caused by infection, the breakdown of a wound after surgery, an ulcer , or a cancer .

frozen section A sample of tissue obtained in a biopsy is frozen, then sliced very thinly and the slices (frozen sections) are examined under the microscope.