Synechia

SYNECHIA, synechia (from Greek synecho—I hold together, I connect), syn. adhesion (Latin adhaesio), a term used to denote various pathological connections between adjacent organs or surfaces. Most often, synechiae are observed in the serous cavities of the pleura, pericardium, and peritoneum, as well as in the anterior chamber of the eye; less frequently, the term synechia is used to denote connections of other parts (e.g., opposing walls of hollow organs, the surface of a fetus with its membranes). By origin, all synechiae can be divided into congenital and acquired (or newly formed). Congenital synechiae are cords and connections between organs (usually of the abdominal cavity) that are the result of maldevelopment of the corresponding parts or the result of the persistence of certain cord-like structures that should have disappeared by birth (for example, the persistence of the vitelline duct cord in the abdominal cavity). Acquired or newly formed synechiae are consequences of the so-called adhesive process, which is based on the organization of inflammatory effusions, hemorrhages, etc. Most often, this involves fibrinous inflammation affecting both contacting surfaces of a serous cavity; the organization of fibrinous exudate, i.e., its resorption and replacement by connective tissue, occurring on both contacting surfaces, leads to these two surfaces growing together by means of a connective tissue synechia. A detailed study of the histogenesis of synechiae shows that the process of synechia formation can proceed in one of five ways (Graser): 1) direct connection solely by means of proliferating epithelium (endothelium); 2) death of the epithelium and connection by means of the proliferation of subepithelial connective tissue; 3) exudation and the penetration of fibroblasts into it; 4) exudation and its organization by means of connective tissue and blood vessels; 5) suppuration and granulation of the membranes with subsequent scarring of the granulation tissue. At one time, there was great debate regarding the participation of the epithelium (endothelium) of serous cavities in the formation of synechiae. At present, after the works of Marchand and Herzog, it can be considered established that it is possible for serous epithelial cells to transform into fibroblasts. On the other hand, fibroblasts of the peripheral layers of a synechia also transform into cells indistinguishable from serous epithelium. To the naked eye, synechiae appear as flat, membranous, or cord-like, thread-like, and finally reticular dense connective tissue connections between contacting parts. Under a microscope, synechiae are found to consist of connective tissue, sometimes with inflammatory infiltrates; this connective tissue contains a certain number of blood vessels; the nerves sometimes encountered are branches of the nerve trunks of the serous membrane, as if drawn into the synechia. Bundles of smooth muscle fibers, often observed in synechiae of the abdominal cavity, are, as most researchers believe, the result of passive traction of muscle tissue from the wall of the intestine or uterus, etc., into the synechia. At the same time, there is data that muscle fibers in synechiae subjected to periodic stretching can form from connective tissue through metaplasia. Flat cells, quite similar to the cells of the serous epithelium, are located on the surface of the synechia. In cases where synechiae are extensive and occupy a significant part or the entire cavity, one speaks of obliteration. To study the topography of synechiae in the pleural cavities, Melnikov-Razvedenkov proposed a special method of autopsy, which consists of cutting the intercostal spaces before beginning the autopsy and studying the arrangement of the synechiae through these incisions. A. Abrikosov.