The pulmonary ligament is not a true ligament but rather the reflection of the mediastinal parietal pleura below the lung root on each side. In this area, the pleura is thrown out into a loose fold that projects medially and connects with the contralateral pleura in the region between the aorta and oesophagus.
Inferiorly, it ends with a free margin. The parietal and visceral layers are in very close apposition within the fold and there is continuity with the bottom of each lung root which lies superiorly.
Hence, in a manner akin to the pleural recesses, the pulmonary ligaments provides a potential space for the expansion of lung tissue. In this case, the expansion is required for:
- inferior movement of the lung root with inspiration
- expansion of the pulmonary vein
Occasionally, an aberrant pulmonary artery originating from the aorta may be found in the pulmonary ligament.