Infiltration

INFILTRATION, infiltrate (from Latin infiltrare - to pour in), a term used in normal and pathological histology, as well as in clinical practice, to denote the processes of penetration into tissues of various cellular elements (the mass of these latter is called an infiltrate in such cases) and also certain chemical substances (e.g., fatty, glycogen infiltration). Often (always in inflammatory infiltrates), along with formed elements, fluids also participate in infiltration, mainly blood plasma exuding from vessels. The impregnation of tissues with fluids, without an admixture of cells, is however designated by other terms, such as: edema, imbibition. Infiltration - as a normal, physiological process - occurs in the differentiation of certain tissues and organs, for example in the formation of the thyroid gland, lymph nodes (infiltration of the organ's reticular basis by lymphoid cells), in the process of resorption of the tail in a tadpole, etc. The greatest significance belongs to pathological infiltrations; these primarily include infiltration by cells of inflammatory origin (inflammatory infiltration - see Inflammation), and in corresponding cases one speaks of leukocytic, eosinophilic, round-celled, hemorrhagic, etc., infiltration. Tissues are often infiltrated by cells of neoplasms (cancer, sarcoma); in such cases one speaks of infiltration of tissues by a tumor, of the infiltrative growth of a tumor. Macroscopically and clinically, infiltration is recognized by the increase in volume of the given tissues, their density, sometimes their tenderness (inflammatory infiltrates), as well as by the change in color of the tissues themselves; thus, infiltration by leukocytes gives the tissues a gray-green tint, by lymphocytes - pale gray, by erythrocytes - red, etc. The fate and significance of cellular infiltrates vary depending on the nature of the process and the cells of the infiltrate; for example, in leukocytic inflammatory infiltrates, the enzyme-like proteolytic substances released upon the breakdown of leukocytes often produce an effect of melting the infiltrated tissues and the development of an abscess; cells of lymphocytic infiltrates partly emigrate back from the tissues, partly break down, and partly go to build new permanent tissue elements. Infiltration by tumor cells as a rule leads to the obliteration of the pattern of the previous tissue, its atrophy, and disappearance. Infiltration with significant destructive changes in the main tissues subsequently most often leads to persistent pathological changes in the form of scleroses, hardenings, decrease or loss of their function; loose, especially transient (e.g., island-inflammatory) infiltrates usually do not leave special traces. - Special mention is due to the so-called round-celled infiltrates, also called small-celled. In most cases, such infiltration indicates the presence of a chronic inflammatory process in the tissues, as a result of which sclerotic and scar changes are so frequent against the background of such infiltrates. But round-celled infiltrates are not always a sign of inflammation: they can also be observed in certain other disorders of tissue metabolism, e.g., in the stroma of the thyroid gland in Basedow's disease, in atrophic changes of the parenchyma of various organs as an initial regenerative act on the part of the organ's connective tissue elements. Such infiltrates can also be an expression of extramedullary hematopoietic processes, such as, for example, lymphocytic infiltrates and lymphomas in various organs in lymphocytic leukemia. Finally, in some cases round-celled infiltrates cannot be considered a pathological process at all, and the cells of the infiltrate, externally resembling lymphocytes, are in reality young forms of the developing sympathetic nervous system: such are, for example, groups of sympathogonia in the medulla of the adrenal glands. Infiltration. Davydovsky. Infiltration l atin o zn aya, a designation used mainly in relation to tuberculous caseous pneumonia in those cases when the affected area on a section has a uniformly gray or yellowish-gray, smooth and translucent appearance, resembling gelatin swollen in water (German 'glatte Pneumonie'). The matter concerns tuberculous pneumonia with the participation of fibrin in the alveolar exudate, and the peculiar swelling of the fibrin probably causes the aforementioned picture. Subsequently, in the areas of infiltration, on a uniform translucent background, dull yellowish specks appear, which is based on focal fatty degeneration of the alveolar epithelial cells lying among the exudate. The outcome of the latinous infiltration is either resorption of the exudate and resolution of the pneumonia or transition to caseous degeneration and the formation of foci of liquefaction and disintegration.