Anatomy of the Left Lower Lobe

Pulmonary Arterial Anatomy

• The superior segmental branch is the first arterial branch to the left lower lobe.
• A single branch to the superior segment occurs 72% of the time; two branches, 26%; and three branches, 2%.
• The superior segmental branch arises after the posterior branches to the left upper lobe and before the lingular branches.
• Lingular branch to the upper lobe originates from the superior aspect of the ongoing pulmonary artery.
• The pulmonary artery transitions into the common basilar trunk, which bifurcates into anterior and posterior branches for basal segments.
• In 3.5% of cases, a branch from the posterior segmental artery supplies the superior segment of the left lower lobe.
• Access to pulmonary arterial branches is through the oblique fissure; these arteries are located anterior to the airway branches.

Venous Drainage

• Left inferior pulmonary vein drains the left lower lobe, formed from the superior segmental vein and common basal veins.
• The left inferior pulmonary ligament must be divided to approach the left inferior pulmonary vein.
• Superior segmental vein occasionally enters the pericardium separately from the common basal vein.

Bronchial Arteries and Lymphatics

• Bronchial arteries, arising from the aorta, supply oxygenated blood to central airways and large pulmonary vessels, making up 3-5% of cardiac output.
• Knowledge of airway and vascular anatomy is crucial for lung surgeries.
• Airways and pulmonary arteries are centrally located; pulmonary veins are peripheral and intersegmental.
• Variations in lung structures exist; airway anatomy is more consistent than pulmonary venous anatomy.
• Pulmonary lymphatics are located in both central and peripheral segments, aiding in the evaluation of lymph node metastases in lung cancer patients.

Historical Classification of Lung Anatomy

• The anatomical classification system dates back to the 1800s, created for drainage procedures of intrapulmonary infections.
• Ewart first proposed a system in 1889; Kramer and Glass described the bronchopulmonary segment in 1932.
• Jackson and Huber formalized a nomenclature with 18 bronchopulmonary segments in 1943.
• Two classification systems exist: Jackson-Huber (18 segments) and Boyden (20 segments), the latter splitting the left upper lobe into B1 and B2 segments.

Lung Structure and Density

• Lungs have a functional residual capacity of approximately 2.5 L in an adult; density varies across segments.
• The right lung has three lobes (upper, middle, lower) while the left lung has two lobes (upper, lower), due to the liver's upward projection.
• Each pulmonary lobe is encased in pleura, with bronchopulmonary segments having unique airway, arterial, and venous supplies.

Interlobar Fissures

• The right lung has two fissures: horizontal and oblique; the left lung has only an oblique fissure.
• Fissures enable independent movement of lung lobes.
• The bronchus intermedius is the continuation of the right mainstem bronchus, leading to the middle and lower lobe bronchi.

Lymphatic Drainage Patterns

• Each pulmonary lobe has a distinct lymphatic drainage pattern with significant nodes such as the sump node.
• Right lobes drain through right paratracheal or subcarinal nodes; left lobes primarily through subcarinal nodes.
• Understanding lymph node mapping is critical for non-small cell lung cancer staging and surgical planning.

This quiz focuses on the vascular anatomy of the left lower lobe, specifically the superior segmental branch's variations. Explore statistical data about the number of branches and their anatomical relationships with other branches. Test your knowledge on pulmonary anatomy and branching patterns.