CT Pulmonary Angiography > PA Anatomy > Right Lung > RIght Lower Lobe

PA Anatomy: Right Lower Lobe

Caudal to the origin of the right middle lobe arteries, the interlobar artery becomes the right lower lobe artery. At about the same level as the origin of the right middle lobe arteries and opposite to them, the right lower lobe artery gives off the posteriorly oriented artery to the superior (apical) segment of the right lower lobe (A6). However, in approximately 20% of individuals, A6 arises as two or very rarely three separate arteries from the right lower lobe artery (7,9,12). There are often three identifiable subsegmental arteries within the superior segment of the right lower lobe (A6a, A6b, and A6c), any two of which may have a common Trunk (7).

Caudal to the origin of the artery to the superior segment of the right lower lobe, the right lower lobe artery is renamed as the pars basalis, or basal trunk (11). In approximately one-half of individuals, the order of branching from the pars basalis is first the medial basal segmental artery (A7), then the anterior basal segmental artery (A8), and finally the lateral and posterior basal segmental arteries (A9 and A10) (9). A7 and A8 may arise as a common trunk (A7+8), as may A9 and A10 (A9+10), the former coursing anteromedially and the latter coursing posterolaterally.6 The order of branching from the pars basalis is frequently random, however (9). Other variations can be seen, such as the absence of A7 (9); or the branching pattern of A7 and A8+9+10 (12). Although one basal segmental artery around a segmental bronchus is the prevailing pattern, two or even three subsegmental arteries around a segmental bronchus may be seen (12).

An inconstant subsuperior pulmonary segment is seen in approximately 30% of individuals, located between the superior and basal segments of the lower lobes bilaterally (7). If present, its pulmonary arterial supply is denoted as A8, and this artery generally takes origin from the lateral aspect of the right pars basalis. It has a single stem in the majority of cases, although two and three stems are sometimes seen (7).