Inferior lobe of right lung

The inferior lobe of the right lung (Right lower lobe) is the largest of the three lobes of the right lung. It is situated below and posterior to the oblique (major) fissure, which separates it from the right upper lobe superiorly and the right middle lobe anteriorly. The horizontal (minor) fissure does not directly border the inferior lobe; rather, it separates the upper and middle lobes anteriorly.

Boundaries and Relations

• The superior surface of the right lower lobe is defined by the right oblique fissure, which typically originates posteriorly at the level of the fifth rib (or T3-T5 vertebral level), courses anteroinferiorly along the sixth rib in the mid-axillary line, and reaches the anterior third of the hemidiaphragm inferiorly.

• The inferior surface rests on the right hemidiaphragm. In living patients, the lung extends deep into the posterior costophrenic (diaphragmatic) sulcus, reaching at or below the level of the 12th rib in approximately 80% of individuals, and as low as the body of L1 in 18%.

• The medial surface is related to the vertebral column, the esophagus, the azygos vein, and the inferior vena cava. The inferior pulmonary ligament anchors the lower lobe medially.

Bronchial Anatomy

The right inferior lobe is ventilated by the right lower lobe bronchus, which arises as the continuation of the right main bronchus after the takeoff of the right upper lobe bronchus and the bronchus intermedius. The most common branching pattern includes five segmental bronchi: the superior segment (B6) and four basal segments medial basal (B7), anterior basal (B8), lateral basal (B9), and posterior basal (B10). Variations in this branching pattern are common, occurring in roughly four distinct configurations.

Vascular Supply

The segmental pulmonary arteries generally lie toward the lung periphery relative to their corresponding bronchi (anterior, lateral, or posterior), while the segmental veins of the inferior pulmonary vein lie central to the bronchi (posterior, medial, or anterior). The arteries may be single, duplicate, or even triplicate within individual segments.

Fissural Completeness

The right oblique fissure separating the inferior lobe from the upper and middle lobes is complete in approximately 64-77% of individuals and incomplete in the remainder, with fusion between lobes most common posteriorly near the hilum. Incomplete fissures can affect collateral ventilation, disease spread, and surgical planning. Accessory fissures most commonly the inferior accessory fissure are present in approximately 6% of right lungs and may create the appearance of an additional sublobe within the right lower lobe.