CT Pulmonary Angiography > PA Anatomy > Left Lung >Left Upper Lobe

PA Anatomy: Left Upper Lobe

The LPA arches over the superior aspect of the left upper lobe bronchus to first supply the left upper lobe. There is no left truncus anterior, and there tend to be more separate branches scattered along the course of the left pulmonary artery than there are along the course of the right pulmonary artery (3). The left upper lobe pulmonary arterial branches may arise in fairly random order, and they frequently form small trunks of two or more branches (9). Two to seven branches may originate from the proximal LPA to supply the left upper lobe and lingula (Figure 1b, 1c) (8-9). The anterior segmental pulmonary arterial supply (A3) arises from the anterior aspect of the mediastinal portion of the LPA (pars anterior), and A3 typically subdivides into three portions (A3a, A3b, and A3c) (10). The subsegmental A3 arteries may arise as separate branches from the LPA, however. A3 or a subsegmental branch of it has a common trunk with part or all of A1+2 in approximately 40% of individuals (7). Occasionally, A3 may arise from the posterior aspect of the LPA; and occasionally, A3a may arise from the left interlobar artery(7,10).

The apicoposterior subsegmental arteries (apical, A1+2a; posterior, A1+2b; and lateral, A1+2c) usually arise from the most superior or slightly posterior portion of the mediastinal portion of the LPA, superior to the interlobar segment.10 In approximately one-half of individuals, A1+2a and A1+2b arise as a common trunk, with A1+2c arising separately.10 In approximately 15% of individuals, all three subsegmental arteries arise as a common stem, paralleling the apicoposterior segmental bronchus (7,10). Less frequently but not uncommonly, one may see separate origins of each subsegmental artery, or a common trunk of A1+2b and A1+2c with separate origin of A1+2a (7,10). Again, A1+2 is associated with A3 in some way in approximately 40% of individuals (7).

The lingular arteries (superior lingular, A4; inferior lingular, A5) arise from the anterior aspect of the left interlobar artery in approximately 90% of individuals; in the remainder, they arise with other upper lobe vessels from the pars anterior of the mediastinal LPA.7,9,11 They may arise as a single trunk or as two separate arteries.