Contributor: Gordon K. Klintworth
Hypoplasia is a congenital anomaly that affects many different organs and tissues, including the adrenal gland [hypoplasia - adrenal gland], cerebellum [hypoplasia - cerebellum], dermis [hypoplasia - dermis], epiglottis [hypoplasia - epiglottis], gastrointestinal tract, gonads [hypoplasia - gonad], heart, lung [hypoplasia - lung], paranasal sinuses, parathyroid glands [hypoplasia - parathyroid gland], salivary glands [hypoplasia - salivary gland], skin [hypoplasia - skin], spleen [hypoplasia - spleen], thyroid gland [hypoplasia - thyroid gland], teeth [hypoplasia - teeth],  thumb [hypoplasia - thumb], ulna [hypoplasia - ulna], and thymus [hypoplasia - thymus].
Specific parts of the eye may be hypoplastic: ciliary body [hypoplasia - ciliary body], iris [hypoplasia - iris], fovea [hypoplasia - fovea], macula [hypoplasia - macula], optic nerve [hypoplasia - optic nerve], and puncta [hypoplasia - puncta].
Pulmonary hypoplasia occurs in some diseases that affect the eye (Potter syndrome, trisomy 21, trisomy 13). Hypoplasia of the lymphoid tissue results in an immunodeficiency state involving B-cells and T-cells. The rare congenital agenesis of the pituitary gland is accompanied by adrenal gland hypoplasia, thyroid hypoplasia, and gonadal hyoplasia. Pituitary hyoplasia is rare and most often associated with anencephaly. Hypoplasia occurs in numerous structures in the lacrimo-auriculo-dento-digital syndrome, including the puncta, thumb, lung, and salivary glands. Focal dermal hypoplasia is associated with ophthalmologic manifestations. Although hypoplasia is a congenital anomaly smaller than normal organs or tissues with hypoplasia may sometimes be difficult to differentiate from acquired changes resulting from atrophy. In some parts of the body, such as the epidermis and gastrointestinal tract, an acquired diminution in steady-state renewable cells is sometimes loosely referred to as hypoplasia. In these situations there is a loss of the progenitor cells. Examples of this is the disuse hypoplasia of the intestinal mucosa following prolonged parental feeding and the skin lesions of  lupus erythematosus or lichen atrophicus.