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As aplasia or aplasia (from ancient Greek ἀπλασία , Neugriechisch απλασία , neulateinisch aplasia "non-formed") the non-formed is used in medicine of an organ despite existing organ system (as opposed to agenesis hereinafter). During embryonic development , practically every organ can be completely absent. If the organ is too small, it is called hypoplasia .

In vital organs, aplasias lead to fetal death and miscarriage . However, some organs are not vital or their function can be replaced in other ways, for example in the case of paired organs by the organ on the other side. Aplasia can then remain without life-threatening consequences (e.g. aplasia of the gallbladder , a thyroid lobe , a kidney or the genital organs ).

Overall, aplasias are rare (usually <1: 1000) and their exact cause can often not be identified. They are often found under the influence of teratogenic substances ( e.g. thalidomide ), teratogenic viruses or radiation (e.g. due to radioactivity ) (see for example amniotic ligament syndrome ).

The same terminology is used in dentistry with teeth. This means that if teeth are not created (a phenomenon that often occurs with wisdom teeth ), it is a case of dental aplasia. Teeth that are too small are called hypoplastic.

In tumor medicine, patients who have an extreme decrease in white blood cells ( leukocytes ) as a result of cytostatic treatment are referred to as aplastic or in a state of aplasia.


  • Elsevier, Lingen (Ed.): Medicine. Human. Health . Approved special edition. Elsevier (content), Munich; Helmut Lingen Verlag (Ed.), Cologne 2006.

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