Peribronchitis

PERIBRONCHITIS, inflammation of the outer coat of the bronchus, i.e., that layer of connective tissue which lies external to the muscle layer, contains cartilage plates in the large and medium bronchial branches, and connects the bronchus with adjacent parts. Harmful agents causing an inflammatory reaction can penetrate the peribronchial tissue by two pathways: 1) from the lumen side (aerogenic pathway) and 2) via peribronchial lymphatic vessels (lymphogenous pathway). In the first case, the disease process passes directly (per continguitatem) from the epithelium and subepithelial tissue through the elastic and muscle coat to the adjacent connective tissue, and such a transition can, of course, occur the more easily the lesser the strength possessed by the given section of the wall, and primarily the thinner its muscle-elastic layer. Thus, it is quite understandable that the penetration of any harmful agent acting from the lumen into the depths, in particular into the peribronchial tissue, most often occurs in the smallest bronchial branches—the bronchioles, especially in the so-called respiratory bronchioles, where the wall is most delicate and thin and where, moreover, the fixation of everything brought in with the air current is extremely facilitated due to the slowed movement of the latter and because of the presence here of a simple non-ciliated single-layer epithelium. If the harmful agent penetrating with the air is easily destroyed or quickly bound by cells and tissue fluids (labile viruses, many poisonous substances), then its effect manifests itself chiefly at the site of primary application. Otherwise (more stable viruses, dust particles), the irritants that have entered the peribronchial lymphatic clefts begin to move with the lymph current along the bronchus in a proximal direction toward the root of the lung, involving in the process the outer coat of increasingly larger bronchial branches. Thus, the second possibility of the occurrence of peribronchitis (by the lymphogenous pathway) is realized, and in this case, despite significant inflammatory changes in the outer coat, the corresponding part of the bronchial mucosa can be found to be completely intact. Subsequently, a secondary transition of the process to the mucosa from the peribronchial tissue is quite possible, as well as its spread to adjacent alveolar septa. In the latter case, a zone of interstitial pneumonia arises around the affected bronchus, which easily and frequently is complicated by one or other exudative process, as a result of which the bronchus turns out to be surrounded by a more or less wide cuff of condensed lung tissue (so-called peribronchial pneumonia). (For the macro- and microscopic characteristics of peribronchitis, their forms, consequences, and outcomes, see Measles, Pulmonary Tuberculosis.) The etiological factors causing the development of peribronchitis are most often 1) certain acute and chronic infections, such as measles, whooping cough, influenza, tuberculosis (of which the first three have primary importance in pediatric pathology), 2) various dust particles (see Pneumoconiosis), and 3) certain toxic gases (chlorine, phosgene, etc.).