Anteromedial basal segment of left lung

Anterior and medial basal segments are often fused in the left lower lobe, forming the anteromedial basal segment of left lung (cardiac segment) (S7+8).

In the standard Boyden classification of bronchopulmonary segments, the left lower lobe basal segments include the anterior basal (B8), lateral basal (B9), and posterior basal (B10) segments. The medial basal segment (S7/B7) on the left has historically been considered frequently absent or fused with the anterior basal segment (forming a combined "anteromedial basal segment (S7+8)" that is sometimes mis denominate as S8 (that should be only the anterior basal segment if a a medial basal segment S7 is present).

However, a recent large study using 3DCT bronchography found that left B7 is present as a distinct structure in approximately 75.6% of patients, challenging the traditional teaching that it is typically absent. Six distinct branching patterns were identified: [1]

• Type 1 (most common, 61.4%): B7 arises from B8

• Type 2 (6.3%): B7 arises higher than B8B10

• Type 3 (5.5%): B7 arises from B9

• Type 4 (1.6%): B7 arises from both B8 and B9

• Type 5 (0.8%): B7 arises from both B8 and B10

• Type 6 (24.4%): B7 is absent