Superior segmental artery of right lung

The superior segmental artery of the right lung (A6), is the branch of the right pulmonary artery that supplies the superior segment (S6) of the right lower lobe. It arises from the interlobar artery (the inferior trunk of the right pulmonary artery), which courses within the oblique fissure parallel to the bronchus intermedius. A6 branches off posteriorly from the interlobar artery, typically at or just below the level of the middle lobe artery origin, and accompanies the superior segmental bronchus (B6) to perfuse the apical (uppermost) portion of the lower lobe.

Key anatomical features:

• Origin: A6 arises from the right interlobar (descending) pulmonary artery. Notably, in approximately 38.6% of cases, the origin of A6 is proximal to the origin of the middle lobe artery, which is an important variant to recognize during thoracic surgery.

• Number of stems: In the most common pattern, A6 consists of a single arterial stem (~59.590.9% of cases). However, two separate stems are found in approximately 37% of cases, and three stems in about 3.5%, reflecting significant anatomical variability.

• Subsegmental branches: A6 typically divides into subsegmental branches A6a (medial/superior), A6b (lateral/superior), and A6c (posterior) which supply the corresponding subsegments of S6.

• Accompanying structures: A6 runs closely alongside the superior segmental bronchus (B6) and is drained by the superior segmental vein (V6), a tributary of the inferior pulmonary vein.

• Surgical relevance: The superior segment of the right lower lobe is a common site for segmentectomy. Arterial variations including shared origins with basal segmental arteries or anomalous branches communicating with adjacent segments occur in up to 18% of cases and are critical to identify preoperatively using 3D-CT bronchography and angiography (3D-CTBA).