Lateral Basal Segment Region, Detailed Anatomy

Description

Positioned on the lateral aspect of the lower lobe, the lateral basal bronchopulmonary segment (segmentum basale laterale, S9) is shown as a basolateral territory that lies inferior to the superior segment (S6) and posterior to the lateral portion of the anterior basal segment (S8). Its apex points superiorly toward the oblique fissure region, while its broad base descends to the diaphragmatic surface. Segmental boundaries are implied by the expected course of intersegmental veins running in the planes between adjacent basal segments. Clinically, S9 matters because it is a dependent segment in supine patients, so aspiration and postoperative atelectasis often localize here and in the posterior basal segment (S10). Bronchial obstruction in the lateral basal segmental bronchus can produce wedge-shaped peripheral collapse that respects intersegmental planes, a pattern that becomes easier to explain when you can point to the basolateral footprint of S9. Segment-level anatomy also guides thoracic surgeons during video-assisted thoracoscopic (VATS) segmentectomy, where identification of the S9 bronchus and segmental arterial branch helps preserve neighboring basal segments and maintain postoperative lung function. A common operative challenge. Use this illustration for teaching bronchopulmonary segmental anatomy in gross anatomy, respiratory system modules, or thoracic surgery training materials, and for annotating radiology or bronchoscopy content that discusses lower-lobe segment localization and dependent disease patterns. Anatomical accuracy verified by SciePro's Medical Advisory Board.