Dictionary

micro- Prefix meaning small, as in microcephaly (small head) and microsomia (small body). The opposite of micro- is macro-.

microangiopathy A disease of the capillaries (very small blood vessels), in which the capillary walls become so thick and weak that they bleed, leak protein, and slow the flow of blood. For example, diabetes predisposes to the development of microangiopathy in many areas, including the eye.

microbe A minute organism typically visible under a microscope. Microbes include bacteria, fungi, and protozoan parasites.

microcephaly An abnormally small head due to failure of brain growth. Microcephaly is an ominous sign because it is almost always associated with developmental delay and mental retardation. Many factors can impair the growth of the brain, including intrauterine infections (such as rubella, cytomegalovirus, and toxoplasmosis), intrauterine chemical exposure (such as in fetal alcohol syndrome),…

microcystic corneal dystrophy See Cogan corneal dystrophy.

microcytic Literally, referring to any abnormally small cell; in practice, referring to an abnormally small red blood cell. For example, microcytic anemia is characterized by small red blood cells. The opposite of microcytic is macrocytic.

microdeletion Loss of a tiny piece—a piece that may be too small to be seen readily through a microscope—from a chromosome. Microdeletions can be detected via high-resolution chromosome banding, molecular chromosome analysis (with FISH), or DNA analysis. Disorders caused by microdeletions include Angelman, DiGeorge, Prader-Willi, and Williams syndromes.

microhematuria See blood in the urine.

microorchidism Abnormally small testes. To determine if the testes are too small, a device called an orchidometer is used that permits a testis to be compared to a series of plastic ovals (like miniature American footballs) of differing sizes. Microorchidism is a diagnostic feature, for example, of Prader-Willi syndrome and certain other multiple malformation syndromes….

menstruation Bleeding that occurs each month if pregnancy does not occur. Also known as menorrhea and menses. See also menstrual cycle.

menstruation, anovular Menstruation that occurs without ovulation. Usually in anovular menstruation the egg that remains in the ovary simply disintegrates, but in some circumstances it is fertilized and a life-threatening ovarian pregnancy results.

menstruation, cessation of The ending of a woman’s menstrual cycles. Menstruation ends naturally in middle age with the onset of menopause. It can also end suddenly as a result of induced menopause. Cessation of menstruation in nonmenopausal women may be due to pregnancy, illness, disorders of the hypothalamus or pituitary gland, medication, stress, overexercise, or…