The hilum of the lung serves as a central point where various structures enter and exit each lung. It functions as a gateway, facilitating the connection between the lungs and the rest of the body’s systems. The hilum allows for the passage of airways, blood vessels, and nerves, anchoring the lungs in place within the chest cavity.
Where the Hilum is Located
The hilum is situated on the medial aspect of each lung. This area is often described as a wedge-shaped or triangular depression found on the central portion of the lung. There is one hilum on each lung, and they lie roughly midway down the lungs, positioned slightly towards the back, closer to the spinal vertebrae. Specifically, the hilum is located between the fifth and seventh thoracic vertebrae.
This region marks the attachment point where the lung root connects the lung to the heart and trachea. The hilum is also where the two layers of the pleura, the protective membranes surrounding the lungs, connect. This connection occurs between the parietal pleura, which lines the chest cavity, and the visceral pleura, which directly covers the lung surface.
What Passes Through the Hilum
The hilum acts as a passageway for a collection of structures that form the lung root, facilitating the lung’s function. The main bronchus, which is the primary airway branching off the trachea, enters the lung through this region, allowing air to move in and out. Alongside the bronchus, the pulmonary artery carries deoxygenated blood from the heart into the lungs for oxygenation. After blood is oxygenated, the pulmonary veins transport this oxygen-rich blood from the lungs back to the heart.
Beyond these major vessels, the bronchial arteries and veins also traverse the hilum, providing a blood supply to the lung tissue itself. A network of nerves, known as the pulmonary plexus, also passes through, helping to regulate lung functions such as breathing and blood flow. Lymphatic vessels and lymph nodes are present in the hilar region as well, playing a role in the body’s immune response and fluid balance. The arrangement of these structures within the hilum can vary slightly between the left and right lung, mirroring the differences in their overall anatomy.
Why the Hilum Matters Medically
The hilum is a significant area for medical professionals, particularly when interpreting imaging studies like chest X-rays and CT scans. Changes in the appearance of the hilum can indicate underlying health issues. For instance, enlarged lymph nodes in this region, a condition known as hilar lymphadenopathy, are a common finding. These enlarged nodes can result from various causes, including infections such as tuberculosis or fungal infections, inflammatory conditions like sarcoidosis, or cancers originating from the lung or spreading from other parts of the body.
Tumors, whether primary lung cancers or metastatic growths, can also appear as masses in the hilar region. Sarcoidosis, a systemic inflammatory disease, frequently causes a symmetric enlargement of the lymph nodes in both hila. Tuberculosis is another notable cause of hilar lymphadenopathy and can sometimes lead to asymmetric enlargement of one hilum. Additionally, conditions that cause elevated pressure in the pulmonary arteries, known as pulmonary hypertension, can lead to visible enlargement of these vessels within the hilum. Recognizing these changes on imaging provides important diagnostic clues for a range of conditions.