MEZARTERIITIS

MEZARTERIITIS, or mesoarteritis (from Greek mesos-middle and arteriitis-artery inflammation), inflammation of the middle coat of arteries; develops in most cases by the process spreading to the middle coat from the intima or adventitia. The causes of M. besides traumatic injuries to vessels include 1) ulcerative atheromatosis (see) with spread to the middle coat, either from the ulcerative process itself or from the perifocal inflammatory reaction, 2) a peculiar arterial disease known as periarteritis nodosa (see Periarteritis), and 3) many acute and chronic infectious diseases, such as abdominal and typhus fevers, pneumonia, influenza, diphtheria, scarlet fever, sepsis, tuberculosis, syphilis, actinomycosis, and some others. In relation to all the acute infections just listed (except typhus fever), the view of Wiesel has prevailed until very recently, according to which the primary factor in arterial lesions was considered to be focal necrosis of the media, followed by an infiltrative-proliferative reaction from the other coats and intermuscular connective tissue, with frequent thrombotic changes in the intima and ending in sclerosis. However, recently more and more data has accumulated in favor of the fact that such a course of the process occurs only in exceptional cases; usually the lesion begins in the intima (degenerative-proliferative changes, thrombosis), and in larger vessels-from the adventitia, where the virus penetrates through the vasa vasorum, causing the development of various inflammatory foci in it. The middle coat, in turn, becomes involved in the process sequentially (although in some cases very quickly), and its reaction is expressed mainly in the destruction of elastic and muscle fibers and in the proliferation of connective tissue cellular elements. Essentially the same course of the process has also been described in typhus fever. For changes in the middle coat of arteries in tuberculosis, actinomycosis, and syphilis, see Artery, Aorta, Actinomycosis. In rheumatism, changes in the middle coat of arteries are also sometimes observed, for example, in the small arteries of the heart, destructive processes in the media and adventitia with subsequent sclerosis have been described. In larger vessels (aorta, aa. mesenterica, renalis, coronaria cordis), specific rheumatic granulomas located near the vasa vasorum of the outer coat and in the adjacent parts of the media have been repeatedly found.