APLASIA (grech, and - otritsa. + plasis formation, education) — one of displays of inborn malformations which is characterized by absence of all body, its part, the site of fabric, a part of a body or all germ. As the synonym is often used the term «agenesia» (grech, genesis an origin, emergence).
Some authors distinguish the terms «agenesia» and «aplasia», considering that they speak about an agenesia at total absence of body and its rudiment, and about And. — when the body is presented only by its rudiment deprived of typical structure. However such body reduced in sizes deprived of typical structure usually is considered as a hypoplasia. Thus, the aplasia and an agenesia should be considered as synonyms. In hematology the term «aplasia» is used not quite legally in relation to the acquired changes (e.g., «an aplasia of marrow» — a panmyelophthisis).
Reasons And. the external teratogens (physical, chemical, biological) influencing an embryo directly or indirectly through an organism of mother are. The same factors, affecting gametes of parents (or more remote ancestors), can cause chromosomal diseases with And. this or that body (fabric) or hereditarily the caused inborn defect with And.
Pathogeny (formal genesis) And. speaks: 1) lack of formation of a rudiment of body (e.g., primary kidney); 2) death of a rudiment of a germ (some forms of «an empty fetal bag»); 3) lack of education or death of other body exerting impact on development of the first (e.g., And. a rudiment of an ureter conducts to And. metanephros). The teratogenetic terminatsionny period (the deadline, later to-rogo this inborn defect cannot arise) is limited at the majority And. first month of an antenatal life.
And. it can be observed in any human organ (a brain, a spinal cord, heart, easy, urinogenital bodies, etc.). And. hearts (acardius) it is observed only at twinning inborn defects. And. one of pair bodies usually causes a vicarious hypertrophy of another. And. one closed gland can cause hypo - or a hypertrophy of other glands. Can be And. only parts of any body, napr, rhinencephalon (arinentsefaliya), corpus collosum etc. Focal And. fabrics it can be observed in skin, most often on a pilar part of the head where at the birth of the baby the defect which is usually not exceeding 5 cm in the diameter is found. And. skin it can be combined with And. more deeply than the located fabric, napr, at various forms of dysraphias (not closing of embryonal cracks).
Practical value has focal And. a muscular layer went. - kish. path. It meets seldom. Defects of a muscular layer, often multiple, are located usually in a cross colon, the area of each defect does not exceed 1 — 2 cm 2 . On site such defects there are pressure diverticulums which in the subsequent are perforated, most often during the first two days of an extrauterine life that leads to diffuse peritonitis (see). Focal And. bones of a skull («a fenestrated skull») it is characterized by the through bone defect of different size and a form at not changed skin most of which often is localized in a parietal or frontal bone. The endosteum and a periosteum in the place of bone defect are usually kept. Focal And. leads diaphragms to false phrenic hernia (see. Diaphragm ). And. can be of nervous cells of an auerbakhovsky texture an etiology of Girshprunga (see. Megacolon ). The most frequent form A. internals is unilateral And. kidneys, are very rare — bilateral And. kidneys I And. spleens. In the world literature some tens of cases are described And. spleens, edges it is usually combined with other heavy inborn malformations.
Can be And. and separate parts of a body, most often extremities. And. it can be observed as in distal (lack of one or several fingers — an adaktiliya, brushes — an akhiriya), and in their proximal part [lack of a hip and shin or shoulder and forearm at preservation of foot or brush — a fokomeliya (from grech, phoke a seal and melos an extremity since extremities are similar to flippers of a seal)]. And. distal parts of extremities it is necessary to distinguish from the pre-natal amputation caused most often by amniotic threads (see. Amniotic threads, banners, unions ). Can be And. the heads — headless freaks (acephalus).
And. all germ it is observed during the early periods of an antenatal life and shown by «an empty fetal bag» (fetal membranes without embryo), however the last phenomenon can arise not only at And. a germ, but also at his death with the subsequent autolysis.
At a vesical drift (see) a germ also, as a rule, is absent. And. it can be observed not only in constant fabrics of a fruit, but also in an afterbirth (a placenta, an umbilical cord). So, in a placenta on the limited site there can be no vorsina (a fenestrated placenta — placenta fenestrata). The total absence of an umbilical cord (akhordiya) which always is combined with the malformations of a fruit not compatible to life is seldom observed; it is more often observed And. by one of arteries of an umbilical cord, edge it can be combined with inborn malformations of a fruit.
Influence on an organism And. body, fabric or part of a body variously. Some types And. (anencephalia, amiyeliya, acardius and bilateral And. kidneys) are not compatible to life. Other types can cause heavy disturbances of functions and without surgical correction conduct by death at various age (e.g., phrenic hernia, a disease of Girshprunga). And. parts of an extremity are compatible to life. And. one of pair bodies, napr, unilateral And. kidneys, sometimes it is completely compensated by a vicarious hypertrophy of another and it can clinically not be shown during all life.
See also Malformations .
Bibliography: Gulkevich Yu. V., Lazyuk G. I. and Kulazhenko V. P. Bases of a teratology in modern aspect, Arkh. patol., t. 33, No. 2, page 9, 1971, bibliogr.; Zerbino D. D. Some new data on pathological anatomy and a pathogeny of inborn phrenic hernias, in book: Perinatal pathology and colienterites, under the editorship of Yu. V. Gulkevich, etc., page 209, Minsk, 1964; Krayev-sky N. A. and Shikhodyrov V. V. Changes of bodies of blood formation, Much tomn. the management on a stalemate. annate., under the editorship of A. I. Strukov, t. 8, page 50, M., 1962; Leybman I. G. About malformations of a muscular layer of a large intestine at newborns, in book: Perinatal pathology and colienterites, under the editorship of Yu. Gulkevich, etc., page 206, Minsk, 1964; Willis I. The borderland of embryology and pathology, L., 1962, bib-liogr.
Yu. V. Gulkevich, V. P. Kulazhenko.