Subsuperior segmental artery of left lung

The subsuperior segmental artery of the left lung (A*) is the pulmonary artery branch that supplies the subsuperior segment (S*), an atypical (variant) pulmonary segment located in the left lower lobe, situated between the superior segment (S6) and the basal segments (S8, S9, S10).

Definition and Anatomical Context

The subsuperior segment (S*) is defined by the presence of a distinct subsuperior segmental bronchus (B*), which arises from the lower lobe bronchus between the origin of the superior segmental bronchus (B6) and the basal segmental bronchi. The subsuperior segmental artery (A*) accompanies this bronchus and provides the arterial blood supply to the parenchyma of S*. In standard pulmonary segmental nomenclature, the lower lobe is classically divided into a superior segment (S6) and four basal segments (S7-S10); S* represents an additional, supernumerary segment that is not universally present.

Key Anatomical Characteristics

• Prevalence: The subsuperior segment is present in approximately 32% of individuals overall, with a slightly higher prevalence on the right (18.8%) than on the left (15.8%) in a large multicenter study of 2,194 CT scans.

• Arterial supply: In the vast majority of cases (89.3%), the subsuperior segment is supplied by a single pulmonary artery (A*), though approximately 10.7% of cases have two arterial branches.

• Bronchial anatomy: Only one bronchus (B*) is detected per unilateral subsuperior segment, with an average diameter of 2.53 ± 0.61 mm. In the left lung specifically, B* was identified in 24.0% of patients (129 of 537) in a 3D-CT study. About half of left-sided B* branches course in a dorsolateral direction.

• Intersegmental boundaries: The intersegmental vein between S6 and S* is consistently complete, providing a reliable anatomical landmark. However, the intersegmental vein on the basal side of S* is absent in approximately 59.7% of cases where B* is present, which can complicate segmental identification during surgery.

• Volume: The average volume of the subsuperior segment is approximately 52.81 ± 21.96 cm³.

• Relationship to the posterior pulmonary lobe: In cadaveric studies, B7 (medial basal bronchus) tends to form a common trunk with B* (subsuperior bronchus) or B8 (anterior basal bronchus), and the subsuperior segment may be associated with the posterior pulmonary lobe, an anatomical variant defined by an aberrant horizontal fissure on the costal surface of the lower lobe.