Is it really a levoatrial cardinal vein?

With the advent of computed tomographic interrogation, it is increasingly frequent to find venous channels that provide direct connections between the pulmonary and systemic veins. These channels, before the introduction of three-dimensional techniques for clinical imaging, were usually found providing an "overflow" for the obstructed left atrium in settings such as hypoplastic left heart syndrome, or divided left atrium. Similar channels, however, had been described almost 100 years ago, with one accurately described as a jugulo-pulmonary vein. Nowadays, however, it is much more usual to find the channels described as levoatrial cardinal veins, even though it is recognized that they are not "levo," often not "atrial," and for sure not "cardinal." In this review, we assemble the evidence supporting the notion that they are better considered as pulmonary-to-systemic collateral channels. We emphasize their similarity, in terms of development, to the sinus venosus and coronary sinus defects.