Anterior segment of left lung

The anterior segment of the left lung (S3) is one of the segments of the left upper lobe (LUL). The left upper lobe is commonly described as having four segments: the fused apicoposterior segment (S1+2), the anterior segment (S3), and the two lingular segments (S4 and S5). The anterior segment occupies a central position within the left upper lobe, situated between the apicoposterior segment superiorly/posteriorly and the lingula inferiorly.

Anatomical boundaries and relationships:

• The anterior segment is supplied by the anterior segmental bronchus (B3) and the anterior segmental artery (A3), which originate from the left upper lobe bronchus and the left pulmonary artery, respectively. A3 characteristically originates at a relatively high position and takes a descending course along the anterior surface of the lung.

• The lateral branch of the posterior segmental vein (V3b) runs horizontally between the anterior segment and the lingula, serving as an anatomic landmark dividing these two regions.

• An accessory fissure known as the left minor fissure may separate the anterior segment from the superior segment of the lingula; this fissure is anatomically present in 818% of left lungs, though it is radiographically visible in only about 1.6% of chest radiographs.