Microangiographic study of the vasa vasorum of the thoracic aorta.

Abstract

The present is concerned with the application of microradiography to the study of the vasa vasorum of the thoracic aorta. Relatively little attention has been given to these small vessels, though the work of Woodruff (1926) Winternitz et al. (1938), and Celestino da Costa (1945) may be mentioned. The walls of the main arterial vessels consist of three layers. (a) The intima is formed by the endothelium, which is an element common to the whole vascular tree and the agent for the metabolic exchange between the blood and tissues. (b) The media, formed essentially by elastic tissue, is limited internally by the internal elastic membrane and externally by the external elastic membrane, which as a rule is less constant and less differentiated than the former. (c) The adventitia consists of connective tissue and elastic fibers. The nutrition of the arterial wall is provided by a network of small vessels, the vasa vasorum. The observation that vessels less than 1 mm. in caliber had no vasa vasorum led Petroff (1922) and Anitschkow (1925) to demonstrate diffusion of plasma through the vessel wall. They injected dogs intravenously with trypan blue and found, on sacrificing the animal, that the aortic wall was tinged blue in its internal third, where there are no vascular structures. In animals that were allowed to live longer, the entire aortic wall was stained blue. Thus it was shown that substances in suspension in the blood could diffuse from the lumen of a vessel into its walls. This interstitial diffusion of the plasma is a relatively slow process and demonstration of its essential mechanism is difficult. The vasa vasorum arise mainly from the collateral branches of the aorta, and only rarely from the aorta itself, the collaterals involved being the coronary arteries, the intercostal arteries, and the lumbar arteries and other branches of the abdominal aorta. The vasa vasorum form two layers, one lying superficially on the adventitia and the other forming the main network in the adventitia. The system originating in anyone collateral anastomoses withthose of neighboring systems, producing a true perivascular “sleeve.” The type of network in the thoracic aorta is slightly different from that in the abdominal aorta due to the fact that the intercostal arteries are situated posteriorly. This produces aricher network in the posterior aortic wall. In the abdominal aorta (which has major vessels arising anteriorly) the network is more uniform. da Costa (1945) called attention to accentuations of the network at the level of the diaphragmatic hiatus, the celiac axis artery,and the bifurcation of the aorta. He thinks that these may have a functional significance in relation to the regulation of the circulation. The vessels of the adventitia supply blood to the deep layers of the arterial wall. The depth to which they reach is, however,a matter of controversy.