Superior segment of right lung

The superior segment of the right lung (S6) is the most cranial and posterior segment of the right lower lobe. It is a distinct bronchopulmonary segment, meaning it constitutes an independent anatomical and functional unit with its own segmental bronchus (B6), segmental artery (A6), and segmental vein (V6).

Anatomical Definition and Boundaries

The superior segment occupies the apex of the right lower lobe. It is situated posteriorly and superiorly, projecting behind the hilum and lying against the posterior chest wall and vertebral column. Its boundaries are defined as follows:

• Superiorly and anteriorly: bounded by the oblique (major) fissure, which separates it from the right upper lobe and right middle lobe.

• Inferiorly: separated from the four basal segments (medial basal S7, anterior basal S8, lateral basal S9, and posterior basal S10) by a single intersegmental plane a feature that makes superior segmentectomy technically classified as a "simple" segmentectomy.

• Medially: related to the mediastinum and the inferior pulmonary ligament region.

Bronchovascular Anatomy

The segment is supplied by the superior segmental bronchus (B6), which is the first branch arising from the lower lobe bronchus, directed posteriorly. In 96.5% of cases, B6 consists of a single stem; in the remaining 3.5%, it arises as two separate stems. The segmental artery (A6) has a single stem in approximately 59.5% of cases, two stems in 37%, and three stems in 3.5%. The segmental vein (V6) drains into the inferior pulmonary vein and is a single stem in 94.3% of cases. Vascular variations are more common than previously recognized, occurring in up to 18% (arterial) and 11.7% (venous) of cases.

Radiological Landmarks

On chest radiography, the superior segment is identified posteriorly in the lower lobe. The upper portion of the right oblique fissure serves as a key landmark, and its visualization on frontal radiographs may indicate atelectasis or displacement of S6. On CT, the B6 bronchus is the first posterior branch of the lower lobe bronchus, and its corresponding artery and vein can be traced using contiguous axial slices.