The pulmonary trunk carries deoxygenated blood from the right ventricle of the heart to the lung circulation. It is about 5 cm in length and 3 cm in diameter, and arises from the right ventricle base above and left to the supraventricular crest. It is a short vessel, arising from the pulmonary conus of the right ventricle at the pulmonary semilunar valves. The trunk has an ascending and posterior orientation, in front of the ascending aorta toward its left aspect (Fig. 10.1). The pulmonary trunk lies totally within the pericardium. It divides into the left and right pulmonary arteries, with each artery about the same size. The bifurcation of the main pulmonary artery varies in appearance, its angle ranging between 100 and 180° (Fig. 10.2). The diameter of the right pulmonary artery ranges between 17 and 30 mm (mean, 23.4 mm). The caliber of the main pulmonary artery is between 20 and 30 mm (mean, 26.4 mm). The sum of the diameters of the left and right main branches is greater than the diameter of the main pulmonary artery.

Three-dimensional (3D) volume rendered computerized tomographic (CT) images emphasize the central location of the bifurcation of the main pulmonary artery into the left and right pulmonary arteries. From a frontal view, the right pulmonary artery disappears from view as it passes under the aortic arch. A posterior view with the aorta and spine cut away gives a good illustration of the superior position of the pulmonary arteries in relation to the pulmonary veins (Fig. 10.3).

The right pulmonary artery is only slightly smaller in caliber than the main artery, as seen in angiograms. It runs a horizontal, sometimes slightly downward, course across the heart image on the frontal view, to the hilum of the right lung, where it divides into superior and inferior branches. It lies behind the ascending aorta and the superior vena cava and in front of the tracheal bifurcation and esophagus (Fig. 10.4).

The right pulmonary artery divides at the right hilum into two main branches: the ascending branch, to the right upper lobe, and the descending branch, to the right middle lobe and the right lower lobe (Figs. 10.5, 10.6, 10.7).

The ascending branch of the right pulmonary artery supplies the right upper lobe, coursing upward for a short distance, and divides into three branches: the apical segmental artery, the posterior segmental artery, and the anterior segmental artery.

The apical segmental artery divides into two major rami: the apical and the posterior rami, supplying the apical bronchopulmonary segment of the right upper lobe.

The posterior segmental artery often arises as a trifurcation, with the apical and posterior segmental arteries
supplying the posterior bronchopulmonary segment of the right upper lobe. There are two main rami: a posterior ramus and a lateral ramus.

The anterior segmental artery of the right upper lobe supplies the bronchopulmonary segment of the same name and is the most inferior artery of the trifurcation of the ascending branch of the right pulmonary artery. There are two main rami: an anterior ramus and a lateral ramus.

The descending branch of the right pulmonary artery supplies the right middle and lower lobes. It originates at the bifurcation of the right pulmonary artery and is caudally oriented. The first branch is the middle lobe artery and the superior segmental artery of the right lower lobe. The next branches are the basal segmental artery and the anterior basal segmental artery. The parent vessel splits to form the posterior basal segmental artery and the lateral basal segmental artery. Each branch supplies the correspondingly named bronchopulmonary segment of the right lower lobe.

The middle lobe artery arises from the descending branch of the right pulmonary artery, at the opposite aspect of the origin of the superior segmental artery. It has an anteriorly and inferiorly oriented direction, bifurcating into a lateral and a medial segmental artery, which supply the respective bronchopulmonary segments of the right middle lobe (Fig. 10.6).

The superior segmental artery of the right lower lobe courses posteriorly upward and laterally, supplying the upper part of the right lower lobe. The medial basal segmental artery of the right lower lobe arises as the third major branch of the right pulmonary artery, and just distally to the point of origin of the superior segmental artery. The anterior basal segmental artery of the right lower lobe arises from the anterolateral aspect of the descending branch of the right pulmonary artery, slightly distal to the point of origin of the medial basal segmental artery. The posterior basal segmental artery of the right lower lobe arises together with the lateral basal segment, as a bifurcation of the descending branch of the right pulmonary artery, reaching the most posterior and dependent portion of the right lower lobe. The lateral basal segmental artery of the right lower lobe arises together with the posterior basal segmental artery as a bifurcation of the descending branch of the right pulmonary artery and supplies the lateral basal bronchopulmonary segment (Fig. 10.8).