The term “perihilar region” refers to the area immediately surrounding the hilum, which is the central gateway of each lung. The prefix “peri-” means “around,” defining this location as the zone encircling the lung’s root. This region is a concentrated anatomical area where the main structures connecting the lung to the rest of the body enter and exit. It serves as the junction point for the circulatory and respiratory systems within the chest cavity.
Pinpointing the Location: The Hilum as the Center
The hilum is a wedge-shaped depression on the medial surface of each lung, facing the center of the chest toward the heart and spine. It represents the fixed point where the lung is anchored to the mediastinum. The perihilar region is the tissue and lung parenchyma that radiates outward from this central attachment point.
The location is generally situated near the center of the chest, roughly between the fifth and seventh thoracic vertebrae. Unlike the lung’s outer surfaces, which move against the chest wall, the hilum and perihilar region are fixed in place. This central position makes it an important anatomical landmark for medical imaging studies.
The right hilum is typically positioned slightly lower than the left, primarily due to the way the large blood vessels arch over the main airways. The hilum is the specific entry and exit point, while the perihilar region encompasses the surrounding lung tissue where these structures spread out into the lung.
Key Structures Contained in the Perihilar Region
The perihilar region houses the major components that sustain the lung’s function, collectively known as the lung root. The most prominent structures entering the lung are the main bronchus, the pulmonary artery, and the pulmonary veins. The main bronchus is the large airway that branches off the trachea, channeling inhaled air directly into the lung.
The pulmonary artery carries deoxygenated blood from the heart to the lung tissue to pick up oxygen. Conversely, the pulmonary veins carry the newly oxygenated blood back to the heart for distribution to the body. These three main structures run in close proximity within the perihilar space.
A dense network of hilar lymph nodes is also concentrated here. These nodes function as filtration centers, collecting lymphatic fluid from the entire lung. Smaller structures like bronchial arteries and veins, which supply the lung tissue itself with oxygenated blood, and autonomic nerves also traverse this packed region.
Clinical Significance in Lung Health and Disease
The concentration of major airways, blood vessels, and immune tissue makes the perihilar region a frequent site of disease manifestation. Abnormalities here are often the first signs detected on medical imaging like chest X-rays or CT scans. Radiologists examine this region for changes in size, shape, or density compared to the opposite lung.
One common finding is hilar lymphadenopathy, which is the enlargement of the hilar lymph nodes. This swelling often indicates the body is fighting an infection, such as tuberculosis or a fungal illness. Lymphadenopathy can also signal systemic inflammatory conditions like sarcoidosis or the presence of cancer.
The perihilar region is a common site for the development or spread of malignant tumors, particularly lung cancer. Cancers often originate near the main bronchi or metastasize to the concentrated lymph nodes, leading to a visible “hilar mass” on imaging. The close proximity of blood vessels and airways means that a mass can quickly obstruct airflow or impede blood flow.
The location is also relevant in conditions like pulmonary edema, often associated with heart failure, where fluid accumulates predominantly in the central lung fields. This is sometimes referred to as a “batwing” pattern due to the bilateral, symmetrical consolidation that spreads outward from the hila. Recognizing these patterns helps doctors quickly determine the cause of a patient’s respiratory symptoms.