Anterior segment of right lung

The anterior segment of the right lung (S3) is one of the three bronchopulmonary segments of the right upper lobe. It is situated in the anterior and inferior portion of the right upper lobe, bounded superiorly by the apical segment (S1), posteriorly by the posterior segment (S2), and inferiorly by the right middle lobe, from which it is separated by the minor (horizontal) fissure.

Anatomical features:

• Bronchus: The anterior segmental bronchus (B3) arises from the right upper lobe bronchus and branches into lateral (B3a) and medial (B3b) subsegmental bronchi. A consistent anatomic relationship exists between the medial subsegmental artery (A3b) and bronchus (B3b), with A3b located along the medial aspect of B3b in approximately 90% of individuals.

• Arterial supply: The anterior segmental artery (A3) typically arises from the truncus anterior, the first branch of the right pulmonary artery, which also gives rise to the apical segmental artery (A1). In the anterior segment, the medial subsegmental bronchus is characteristically located lateral to its corresponding pulmonary artery a relationship that is opposite to that seen in the right middle lobe and serves as a reliable CT landmark for differentiating the two lobes.

• Venous drainage: The lateral branch of the posterior segmental vein of the upper lobe serves as an anatomic landmark dividing the anterior and posterior segments.