Anatomical Edge Known as the Inferior Border of the Lung

Description

Curving along the inferolateral thorax, the inferior border of the lung is defined by the sharp peripheral edge where the costal surface turns onto the diaphragmatic surface, creating a thin margin that is most acute anteriorly and becomes blunter posteriorly. Immediately external to this border lies the parietal pleura, with the costal pleura reflecting inferiorly onto the diaphragmatic pleura at the costodiaphragmatic reflection, forming the pleural recess deep to the lower ribs. The relationship is offset: the pleural reflection descends farther inferiorly than the pulmonary margin, leaving potential space at the costodiaphragmatic recess. A clean landmark. Clinically, this edge anchors surface anatomy for pleural procedures, because the lung typically ends higher than the pleural sac at the midclavicular, midaxillary, and paravertebral lines, and that difference determines where you can enter the pleural cavity without puncturing aerated lung. The view also supports interpretation of blunted costophrenic angles on upright chest radiographs, where pleural effusion first collects in the costodiaphragmatic recess, and it clarifies why basal atelectasis or lower lobe pneumonia often tracks along the diaphragmatic surface rather than the costal surface. Small shifts in this border with respiration matter during thoracentesis planning. Use this illustration in thoracic anatomy and respiratory physiology teaching, as well as in procedure guides for thoracentesis, chest tube placement, and pleural ultrasonography that require correct mental mapping of the costodiaphragmatic reflection relative to the inferior lung margin. It also suits radiology and pulmonary medicine publications discussing costophrenic angle pathology and pleural space anatomy. Anatomical accuracy verified by SciePro's Medical Advisory Board.