Superior lingular segment of left lung

The superior lingular segment (S4) of the left lung is one of two segments that compose the lingula, the tongue-shaped projection of the left upper lobe. The lingula is the anatomical counterpart of the right middle lobe and is divided into the superior lingular segment (S4) and the inferior lingular segment (S5).

Anatomical features:

• Location: The superior lingular segment occupies the upper portion of the lingula, situated between the anterior segment (S3) of the left upper lobe superiorly and the inferior lingular segment (S5) inferiorly. It faces the anterolateral chest wall.

• Bronchus: It is supplied by the superior lingular segmental bronchus (B4), which arises from the lingular division bronchus a branch of the left upper lobe bronchus. The lingular division bronchus typically bifurcates into B4 (superior) and B5 (inferior), though variant branching patterns exist in approximately 9% of individuals.

• Vasculature: The arterial supply comes from the lingular branches of the left pulmonary artery. Mediastinal lingular arteries are present in approximately 30% of individuals as an additional or alternative supply. Venous drainage is via the lingular veins, which typically drain into the left superior pulmonary vein, though in about 4% of cases they may drain into the left inferior pulmonary vein.

• Boundaries: The superior lingular segment may be separated from the anterior segment (S3) above by an accessory fissure known as the left minor fissure