Medial basal segment of right lung

The medial basal segment of the right lung (S7; segment VII), is one of the five bronchopulmonary segments of the right lower lobe. It is the most medially and anteriorly situated basal segment, lying adjacent to the mediastinum and resting on the diaphragm.

Anatomical characteristics:

• Bronchus: The medial basal segmental bronchus (B7) is typically the first branch arising from the basal trunk of the right lower lobe bronchus, after the superior segmental bronchus (B6) has branched off. However, B7 may form a common trunk with B8 (anterior basal bronchus) or, less commonly, with the subsuperior bronchus (B), with anatomic variation occurring in up to 20% of cases.

• Vascular supply: The segment is supplied by the medial basal segmental artery (A7), a branch of the right inferior pulmonary artery, and is drained by the medial basal segmental vein (V7), a tributary of the right inferior pulmonary vein. The segmental arteries generally lie peripheral to the bronchi, while the veins run centrally (intersegmentally).

• Boundaries: S7 is bordered superiorly by the right middle lobe (separated by the oblique fissure), medially by the mediastinum, inferiorly by the diaphragm, laterally by the anterior basal segment (S8), and posteriorly by the posterior basal segment (S10). It occupies the medial and somewhat anterior aspect of the lung base.

• Unique to the right lung: The medial basal segment is classically described as a distinct segment only in the right lung. In the left lung, the corresponding region is often combined with the anterior basal segment or is absent as a separate entity due to the cardiac notch.