Coronary arterial anatomy: Normal, variants, and well-described collaterals

This chapter focuses mainly on the normal and variant anatomy of the epicardial coronary system. It presents a brief review of the structure of a normal coronary artery. A normal coronary artery consists of three histologically distinct layers. The innermost layer is the tunica intima or simply the intima. The next layer is the tunica media or simply media. It surrounds the internal elastic lamina, and its composition depends on the type of artery. The final layer is the tunica adventitia or simply adventitia, which is a layer of loose connective tissue surrounding the media. In elastic arteries, this is demarcated by a layer of elastic fibers termed the external elastic lamina. Functional collaterals can develop between the terminal extensions of two coronary arteries, between the side branches of the two coronary arteries, between branches of the same artery, or within the same branch via the vasa vasorum.