Hypoplasia

HYPOPLASIA (from the Greek hypo—below and plas-so—I create, I form), or hypogenesis, is an insufficient development, in terms of size, of a tissue, organ, or the entire organism. By hypoplasia, one understands a reduction of the elements of an organism caused by a delay in their development; hypoplasia represents a long-standing deviation in size, lying below the variational limits characteristic of a given species of animal. Thus, hypoplasia must be classified among congenital malformations. In contrast to this, a subsequent reduction of normally developed tissues and organs bears the name of atrophy (see). Hypoplasia, like all malformations in general, can manifest in all stages of both intrauterine and extrauterine development. Hypoplasia can concern the entire organism, which retains a harmonious structure, and in that case, it bears the name of nanosomia or microsomia (nanosomia hypoplastica). A weakly expressed hypoplasia bears the name of subnanism. Often, the matter concerns the insufficient development of individual organs, for example, the brain (microencephaly), sometimes accompanied by underdevelopment of the spinal cord and limbs, or the underdevelopment of the kidneys, mammary glands with simultaneous infantilism of the sex glands, or the nipples (microthelia), or the uterus. As for the causes of hypoplastic conditions, they can be divided into two groups. In the first place, one must place endogenous factors, where the cause is reduced to anomalies of the initial formation of germ cells on the basis of hereditary characteristics of the organism. Into the second group, one can place all more or less obvious external moments that harmfully influence the growing organism during one period or another of its development, such as, for example, infections (especially chronic ones) or the external environment in the broad sense of the word. As for the genesis of the disorder of growth and development, there are three points of application for etiological factors: 1) the tissue of the growing organism itself, 2) the organs regulating growth, i.e., the endocrine glands, and 3) the nervous system with its vegetative centers. Correspondingly, one distinguishes, insofar as the entire organism is concerned, hypoplastic nanism, endocrinogenic nanism, and cerebral nanism. By dystrophic nanism, one understands such a reduction in development which is caused by a disorder of nutrition in both a quantitative and qualitative sense. Finally, there exist phenomena of insufficient development of unclear and mixed genesis. See also Agenesia, Atresia.