Posterior basal segment of left lung

The posterior basal segment of the left lung (S10; Dorsal basal segment), is one of the bronchopulmonary segments of the left lower lobe. It is defined as the discrete, functionally and anatomically independent unit of lung parenchyma ventilated by the posterior basal segmental bronchus (B10) and supplied by the corresponding segmental pulmonary artery (A10).

Anatomical characteristics:

• Location: S10 occupies the most posterior and inferior portion of the left lower lobe. It rests against the posterior chest wall and the diaphragm, with its base on the diaphragmatic surface and its apex directed toward the hilum.

• Boundaries: It is bordered superiorly by the superior segment (S6), laterally by the lateral basal segment (S9), and anteromedially by the medial basal segment (S7). The intersegmental planes separating S10 from adjacent segments are defined by the intersegmental veins, which run along these boundaries.

• Bronchovascular anatomy: The segmental bronchus B10 arises from the basal trunk of the left lower lobe bronchus. In the most common branching pattern (~80% of cases), the left basal bronchi divide in a bifurcation pattern, with B10 typically sharing a common origin with B9 as a posterolateral trunk (B9+10), though independent branching also occurs. The segmental artery A10 branches from A9+10 and courses dorsally and deeply into the lung parenchyma, making it difficult to identify from the interlobar fissure. The segmental veins drain into the inferior pulmonary vein.

• Subsegments: S10 is typically subdivided into subsegments including S10a (superior/apical), S10b (lateral), and S10c (medial/basal), though anatomic variation is common.