Lung Segmental Anatomy on CT

Overview

This lecture covers the segmental anatomy of the lungs as visualized on CT scans, focusing on bronchopulmonary tree branching and segment identification for both right and left lungs.

Bronchopulmonary Anatomy: General Principles

• The trachea splits into the right and left main bronchi at the carina.
• Each main bronchus divides into lobar and then segmental (tertiary) bronchi.
• Understanding spatial relationships helps identify lung segments better than rote memorization.

Right Lung Anatomy

• Right main bronchus divides into right upper lobe bronchus and bronchus intermedius.
• Right upper lobe bronchus branches into apical (superior), anterior, and posterior segments.
• Bronchus intermedius further splits into middle and lower lobe bronchi.
• Right middle lobe bronchus divides into medial and lateral segmental bronchi.
• Right lower lobe bronchus first gives off the superior segment, then splits into medial, anterior, lateral, and posterior basal segments.
• Posterior segment is the most inferior branch in the lower lobe.

Left Lung Anatomy

• Left main bronchus divides into upper and lower lobe bronchi.
• Left upper lobe bronchus forms an apicoposterior trunk (which soon divides into apical and posterior segments) and an anterior segment.
• The lingular bronchus branches into superior and inferior segments.
• Left lower lobe bronchus gives off the superior segment early, then divides into anteromedial, lateral, and posterior segments.
• The anteromedial trunk divides into separate anterior and medial segments.

Segment Identification on CT Scan

• Segmental bronchi can be followed on axial CT by tracking the airway branches from the carina.
• Upper lobe segments are superior, middle lobe (right) and lingula (left) are anterior.
• Lower lobe segments include superior, medial, anterior, lateral, and posterior branches, with the posterior segment being the most inferior.
• Systematic repetition of CT scan review aids in segment recognition.

Key Terms & Definitions

• Bronchopulmonary segment — Functional lung unit supplied by a segmental (tertiary) bronchus.
• Carina — Point where trachea divides into right and left main bronchi.
• Lobar bronchus — Airway branch supplying a lung lobe (upper, middle, or lower).
• Lingula — Tongue-like projection of the left upper lobe, analogous to right middle lobe.

Action Items / Next Steps

• Practice tracing bronchopulmonary segments on CT scans, especially normal cases.
• Review the color-coded segmental anatomy illustration on Radiopaedia.
• Request clarification or additional tutorials on challenging topics as needed.