Pulmonary Ligament
Definition
The pulmonary ligament is a double fold (sleeve) of pleura that hangs down below the root of the lung between the mediastinal surface of the lung and the mediastinum.
Formation
The pleura surrounds the root of the lung as a cuff. Below the root, this cuff does not end abruptly — instead, the two layers (visceral and parietal/mediastinal) remain in contact and hang down as a loose triangular fold called the pulmonary ligament.
Extent
- Extends from the root of the lung (at the hilum) downwards to the diaphragm
- Lies between the mediastinal surface of the lung and the mediastinum
- At its lower end, it ends in a free crescentic border just above the diaphragm
Contents
- Thin layer of loose areolar tissue
- A few lymphatics
- No major vessels or nerves
Functions
- Dead space for pulmonary vein expansion: The inferior pulmonary vein expands into the pulmonary ligament during increased venous return (e.g., during exercise) — the ligament accommodates this expansion without tearing
- Allows descent of the lung root: During deep inspiration, when the diaphragm descends, the pulmonary ligament allows the lung root (hilum) to descend without the pleura being torn
- Stabilisation: Helps anchor the lower part of the lung to the mediastinum
Relations
| Surface | Structure |
|---|---|
| Anterior (medial) | Oesophagus (right side); descending aorta (left side) |
| Posterior (lateral) | Mediastinal surface of lung |
Clinical Relevance
During pneumonectomy (surgical removal of a lung), the pulmonary ligament is divided to free the lower part of the lung from the mediastinum before removal.
The loose areolar tissue of the pulmonary ligament may allow spread of infection between the mediastinum and the lung along this plane.