Medial basal segmental artery of left lung

The medial basal segmental artery of the left lung (A7) is the branch of the left pulmonary artery that supplies the medial basal segment (S7) of the left lower lobe. It follows the corresponding medial basal segmental bronchus (B7) and provides arterial blood flow to the lung parenchyma situated along the mediastinal surface of the left lower lobe, adjacent to the cardiac silhouette.

Key anatomical features:

• Origin and course: A7 arises from the left interlobar (descending) pulmonary artery as part of the basal trunk. It courses medially alongside B7 toward the mediastinal aspect of the left lower lobe. The segmental artery closely accompanies its corresponding segmental bronchus, generally lying toward the lung periphery relative to the bronchus.

• Diminutive nature on the left: Unlike its right-sided counterpart, the left A7 is characteristically diminutive due to the presence of the heart (cardiac silhouette), which reduces the volume of the medial basal segment on the left side. It is often supplied as a subsegmental branch off the left A8 (anterior basal segmental artery) rather than arising as an independent segmental vessel.

• Variability and prevalence: The left medial basal segment (S7) and consequently its arterial supply has historically been considered frequently absent. However, recent 3D-CT bronchography and angiography studies in 1,440 patients demonstrated that left S7 is present in approximately 75.6% of individuals. Six distinct branching patterns of B7 (and its accompanying artery) have been identified, the most common being B7 arising from B8 (61.4%), followed by complete absence of B7 (24.4%).

• Relationship to other basal arteries: The left lower lobe basal segmental arteries include A7 (medial basal), A8 (anterior basal), A9 (lateral basal), and A10 (posterior basal). In the left lung, the basal trunk most commonly gives rise to two or three arterial stems, with A7 frequently sharing a common trunk with A8 (designated A7+8). Anatomic variations in the number and position of these arteries occur in up to 20% of cases, and the segmental arteries may be single, duplicate, or even triplicate.