Anterior segmental artery of left lung

The anterior segmental artery of the left lung (A3) , is a branch of the left pulmonary artery that supplies the anterior segment (S3) of the left upper lobe.

Origin and course

A3 arises as one of the first branches of the left pulmonary artery, typically originating from its mediastinal (anterior) aspect before the artery enters the interlobar fissure. It is generally the most anteriorly and superiorly positioned segmental artery of the left upper lobe. Embryologically, A3 initially originates at the lung apex and takes a long descending course along the anterior surface of the lung; this high position is subsequently corrected by the increasing volume of the anterior segment (S3) during fetal development.

Relationship to surrounding structures

A3 accompanies the anterior segmental bronchus (B3) and runs in close proximity to the anterior segmental vein (V3). The segmental artery lies toward the lung periphery relative to its corresponding bronchus, while the segmental vein tends to lie more centrally (intersegmentally). A3 is bordered superiorly and posteriorly by the apicoposterior segment (S1+2) and inferiorly by the lingular segments (S4 and S5).

Branching patterns and variability

The left upper lobe exhibits the greatest variability in arterial branching among all pulmonary lobes. According to the Yamashita classification, the most common arterial pattern is Type A, in which A3 arises as a separate branch alongside A(1+2)a+b and A(1+2)c. The left upper lobe is most commonly supplied by four arterial branches from the left pulmonary artery. A3 typically divides into subsegmental branches a lateral subsegmental artery (A3a) and a medial subsegmental artery (A3b) though up to 38 distinct arterial distribution patterns have been described at the subsegmental and sub-subsegmental levels. Notably, 16% of interlobar arterial variations involve the lateral subsegmental artery of A3, which has important implications for segmentectomy planning.