CT Pulmonary Angiography > PA Anatomy > Left Lung >Left Lower Lobe

PA Anatomy: Left Lower Lobe

The left lower lobe bronchus is shorter than the right lower lobe bronchus, so the left lower lobe bronchi and their accompanying arteries originate at a slightly higher level than those on the right (12). The superior (apical) segmental arterial supply (A6) of the left lower lobe originates from the interlobar artery at or above the level of the lingular arteries, usually as a single trunk (in approximately 70% of individuals) (8). However, the superior segmental pulmonary arterial supply frequently arises as two or more separate trunks (8-9). Occasionally, A6 arises from a lingular artery (9). There are often three identifiable subsegmental arteries within the superior segment of the left lower lobe (A6a, A6b, and A6c), any two of which may have a common trunk (7).

Caudal to the origin of the superior segmental artery, the left interlobar artery becomes the pars basalis or basal trunk. There is usually a single anteromedial basal segmental bronchus; and so there is also, in approximately 60% of individuals, a single common pulmonary arterial trunk for segments 7 and 8, denoted as A7+8.8,9,12. However, the artery to the lateral basal segment (A9) frequently arises in this common trunk as well, which would give us the notation of A7+8+9, with A10 arising separately from the pars basalis (11). A9 and A10 also frequently arise as a common trunk, or in other configurations (11). Additionally, the medial basal segmental artery is inconstant, and a true A7 may not be identified. Again, the basal subsegmental arteries may be duplicated or even triplicated around a segmental bronchus (12).

The inconstant subsuperior pulmonary segment is seen in approximately 30% of individuals (7-8). If present, A8 generally takes origin from the posterolateral aspect of the left pars basalis. It has a single stem in the majority of cases, although two and three stems are sometimes seen (7).