CT Pulmonary Angiography > PA Anatomy > Right Lung > Right Upper Lobe

PA Anatomy: Right Upper Lobe

At the right lung hilus, the RPA divides into a superior trunk (the ascending branch or truncus anterior) and an inferior trunk (the descending branch or interlobar artery). The truncus anterior supplies the right upper lobe; and the interlobar artery, which runs in the interlobar fissure and parallels the bronchus intermedius, supplies the right middle and right lower lobes. The truncus anterior (TA) has a course which is anterior to the right upper lobe bronchus, and it usually terminates in the apical (A1) and anterior (A3) segmental arteries, both of which usually divide into paired subsegmental arteries (A1a and A1b, and A3a and A3b, respectively).

The posterior segment has a quite variable pulmonary arterial supply (A2). In approximately one-half of individuals, the pulmonary arterial supply to the posterior segment is split between an ascending artery which arises from the interlobar artery, and a recurrent artery which originates from either the truncus anterior or from A1a (6-7). In this situation, the anterior subsegment is typically fed by the recurrent artery (which becomes named A2a), and the posterior subsegment is typically fed by the ascending artery (which becomes named A2b), and these two arteries have a reciprocal relationship in terms of size and area of distribution (6). In approximately one-third of individuals, the posterior segment's sole supply is from the ascending artery (7). In approximately 15% of individuals, the posterior segment is fed entirely from the truncus anterior (7), in which case there may be no ascending artery. However, the ascending artery is present in approximately 90% of individuals (8-9). It may also on occasion become part or all of A2a and A3, especially if there are two ascending arteries (7-8). (Note that different series report varying proportions of these branching patterns. For example, one study reports that sole supply of the posterior segment by the ascending artery is most common (10))

There is also an inconstant bifurcation of the ascending branch of the RPA into superior and inferior trunks (truncus anterior superior and inferior) and this inferior trunk of the upper lobe artery may supply some or all of the anterior segment (becoming A3, and particularly A3a), in approximately 15-20% of individuals (7-8). This inferior trunk may also arise independently from the superior trunk. The truncus anterior inferior is expected to pass anterior to the anterior segmental bronchus (B3) (8). In any event, the ascending artery is expected to arise from the interlobar artery, caudal to both the superior and inferior trunks of the right upper lobe arterial supply (10).

As mentioned, the anterior segment arterial supply (A3) arises solely from the truncus anterior in the majority of cases, but additional or replaced supply can also be seen from the ascending artery (in approximately 25% of individuals) or from the inferior trunk of the upper lobe arterial supply (in approximately 15%) (7).