Pulmonary Arterial System

The mainstem pulmonary artery trunk arises to the left and posterior to the aorta and then branches into the right and left pulmonary artery. The right pulmonary artery passes directly posterior to the aorta. The right pulmonary artery is longer than the left. No one pattern for either the right or left pulmonary artery is "standard"; however, a relatively uniform distribution occurs for each. The right pulmonary artery is seen in Figure 11.4. The first branch is the truncus anterior branch which divides into apical anterior and posterior segmental arteries. The posterior artery from the truncus anterior supplies only a part of the posterior segment since there is an additional posterior ascending artery arising further down from the pulmonary artery and is found in 90% of people. This is found within the fissure unlike the truncus anterior branch which is found outside the fissure. The posterior ascending artery is important, however, since it must be identified and ligated when performing a right upper lobectomy to prevent major hemorrhage from injuring this unsuspected branch.

The middle lobe artery arises from the right pulmonary artery at the same level as the posterior ascending artery and also at the same level as the superior segmental artery and therefore care must be taken when taking a lobar pulmonary artery to prevent damage to another lobe. The left pulmonary artery is seen in Figure 11.5.

The left pulmonary artery is posterior and superior to the left mainstem bronchus, i.e. the left mainstem bronchus is hyparterial or below and anterior to the left PA, unlike the right side where it is eparterial.

The left pulmonary artery branches into an upper lobe pulmonary artery with an apical artery, an anterior artery and coming off distally, separate posterior arteries. The superior segmental artery to the left lower lobe actually comes off proximal to the takeoff of the lingula artery. This is the most common variant, although a third of the time the superior segmental artery may come off distal to the lingula artery. The left pulmonary artery then continues to the basal artery.

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