Lateral Basal Pulmonary Segment

Description

Arising from the lower lobe (lobus inferior) of the adult lung, the lateral basal pulmonary segment (segmentum basale laterale, S9) occupies the posterolateral portion of the basal pyramid. Its parenchyma lies inferior to the oblique fissure and lateral to the posterior basal segment (S10), with the diaphragmatic surface forming its inferior boundary against the dome of the diaphragm. Segmental anatomy follows the bronchovascular tree, so a segmental bronchus (B9) and its accompanying segmental pulmonary artery branch (A9) course centrally, while intersegmental pulmonary veins mark the planes separating S9 from neighboring basal segments. Clear margins matter. Segment S9 carries real weight in practice because it sits in a gravity-dependent region of the lower lobe, a common distribution for aspiration-related pneumonitis and for dependent atelectasis in supine patients. Thoracic surgeons also rely on S9 boundaries during segmentectomy, where identifying the intersegmental veins and then inflating or staining the target segment helps preserve adjacent parenchyma while achieving oncologic margins for small peripheral non-small cell lung cancers. Radiologists map S9 when localizing nodules on CT and when correlating bronchoscopic navigation paths to the intended subsegmental bronchus. Useful for teaching bronchopulmonary segments in gross anatomy, respiratory anatomy, and thoracic surgery courses, this illustration also supports atlases, operative manuals, and radiology references that need consistent Terminologia Anatomica labeling for the basolateral (lateral basal) segment. It fits well in clinical education on aspiration patterns, lower-lobe collapse, and segment-based resection planning. Anatomical accuracy verified by SciePro's Medical Advisory Board.