Superior segmental artery of left lung

The superior segmental artery of the left lung (A6), is a branch of the left pulmonary artery that supplies the superior segment (S6) of the left lower lobe.

Origin and course

The left main pulmonary artery is a direct posterior continuation of the main pulmonary trunk. Unlike the right side, it does not divide into distinct superior and inferior trunks but instead runs as an interlobar artery within the oblique (major) fissure of the left lung. As the interlobar artery descends, the superior segmental artery (A6) is typically the first branch given off to the left lower lobe, arising from the posterior aspect of the interlobar artery at or just below the level of the upper lobe takeoff. In most individuals (approximately 65.9% of cases), A6 is supplied by a single artery, though duplicate or even triplicate origins have been described.

Territory of supply

A6 supplies the superior segment (S6) of the left lower lobe, which occupies the posterosuperior portion of the lower lobe. This segment is bounded superiorly by the oblique fissure (separating it from the upper lobe) and inferiorly by the basal segments (S8, S9, S10). On the left side, the medial basal segment (S7) is typically diminutive due to the cardiac silhouette and is often supplied as a subsegmental branch off A8 rather than as an independent segment.

Relationship to adjacent structures

A6 runs in close association with the superior segmental bronchus (B6) and the superior segmental vein (V6). The segmental artery closely accompanies the segmental bronchus in approximately 90% of pulmonary segments. V6 tributaries are often double and tend to disperse widely, which is an important consideration during segmentectomy.

Anatomical variations

The origin of A6 on the left side is notable for its relationship to the lingular artery: in approximately 65.9% of cases, the origin of A6 is proximal to the origin of the lingular fissural artery. Variations include a two-stem type (observed in ~24.7% of cases) and a three-stem type (~2.1%). A subsuperior artery (A), when present, is always accompanied by a corresponding subsuperior bronchus (B), found in approximately 24% of cases.