Heterotopia

HETEROTOPIA (from Greek heteros- other and topos- place), atypical localization of tissues or parts of organs, in other words, the presence of them in an unusual place (R. Virchow). Examples of H. can be findings of gastric mucosa in the esophagus, Lieberkühn's glands in the stomach, elements of the pancreas in the intestine, mucosa of the cervical canal of the uterus on the inner surface of the hymen, gray matter of the cerebral cortex in the white matter of the brain, etc. It is accepted (M. Borst and others) that H. is the result of damage or changes in tissue differentiation in early stages of development, but by no means a consequence of the transformation of one tissue into another (see Metaplasia) after the final formation of the organism. The development in the formed organism of the above-mentioned formations from "indifferent" primordia is also not considered possible (Schridde). Thus, heterotopia refers to congenital developmental anomalies (see also Hamartoma, Choristoma). Heterotopia in early stages of embryonic development was produced experimentally by Spemann and his school (1918). It was found that, when tissue is moved from one area of the organism to another, the moved parts do not maintain their structure and do not drop out of further development, but continue to transform into excess organs of a different character. Thus, the pre-epithelial ectoderm of the newt transforms into an excess primordium of muscles (myotomes); the dorsal lip of the blastopore forms a whole axial complex, i.e., the notochord, spinal cord. In most cases, the transplantation site determines the differentiation of the transplanted tissue. These facts, it seems, refute the hypothesis of the embryonic nature of heterotopia and raise the question of the possibility, within certain limits, of metaplasia of the corresponding tissues after their period of differentiation.