A hilar mass, found on imaging like a chest X-ray or CT scan, refers to an abnormal growth or enlargement near the center of the lung. While this discovery often causes concern, a hilar mass is not always cancer, though it requires prompt medical investigation. The term describes the location and appearance of the abnormality, which can represent various underlying conditions, both benign and malignant.
Understanding the Location and Terminology
The hilum, sometimes called the lung root, is the triangular area on the medial surface of each lung where various structures enter and exit the organ. This gateway connects the lung and the central chest cavity. The contents of the hilum include the main bronchi, the pulmonary arteries (carrying deoxygenated blood), and the pulmonary veins (carrying oxygenated blood back to the heart).
The hilum also houses numerous lymph nodes, which are small glands that filter lymphatic fluid. Since these nodes trap foreign particles, infectious agents, and abnormal cells, they frequently become the source of a perceived “mass” when they enlarge (lymphadenopathy). Therefore, a hilar mass is often an enlarged cluster of lymph nodes reacting to a process elsewhere in the body.
Common Non-Malignant Causes
The most frequent causes of a hilar mass are reactive conditions that cause lymph nodes to swell, similar to neck glands enlarging during a cold. Infections entering the lungs often trigger this response, making the hilar lymph nodes prominent on imaging. This reaction occurs with acute respiratory infections, which resolve quickly, or with chronic infections.
Certain fungal infections, such as histoplasmosis (endemic to the Ohio and Mississippi River Valleys) or coccidioidomycosis (in the southwestern United States), are known to cause hilar lymphadenopathy. Tuberculosis, a bacterial infection, frequently presents with enlarged hilar lymph nodes, particularly in children and in regions where the disease is more prevalent. These infectious causes lead to granulomatous inflammation, where the body walls off foreign material.
Another non-malignant cause is sarcoidosis, an inflammatory disease that often results in enlarged lymph nodes. Sarcoidosis characteristically causes bilateral hilar adenopathy, meaning the lymph nodes on both lungs are symmetrically enlarged. Less commonly, a benign tumor like a hamartoma (a localized overgrowth of normal tissue components) can be the source of the mass.
When a Hilar Mass Indicates Cancer
Despite the many benign possibilities, a hilar mass remains a common presentation for several types of cancer. Primary lung cancer, especially those originating in the central airways (like squamous cell carcinoma and small cell lung cancer), frequently develops near or within the hilum. These tumors can arise directly from the bronchial lining or the glandular tissue in the area.
The mass can also represent metastatic disease, which is cancer that has spread from other parts of the body. Cancers originating in the breast, colon, or kidney often metastasize to the chest lymph nodes, including the hilar nodes. Lymphomas, cancers arising from the lymphatic system itself, can also manifest as enlarged hilar lymph nodes.
Certain imaging features raise a stronger suspicion of malignancy. A unilateral mass, affecting only one lung’s hilum, is more suggestive of a tumor than the bilateral enlargement seen with inflammatory conditions like sarcoidosis. Irregular borders, a size greater than one centimeter, and rapid growth increase the likelihood of cancer. Associated symptoms like unexplained weight loss, persistent coughing up of blood, or a history of heavy smoking also factor into the overall risk assessment.
Steps in Diagnostic Investigation
Once a hilar mass is identified, the next step is typically advanced imaging to gather detailed information. A contrast-enhanced computed tomography (CT) scan is commonly used to better define the mass’s size, shape, and relationship to surrounding structures like the bronchi and blood vessels. The intravenous contrast agent helps distinguish between solid tissue (a potential tumor) and simply enlarged blood vessels.
A positron emission tomography (PET) scan is often employed to assess the mass’s metabolic activity. Since cancer cells consume glucose at a higher rate than normal tissue, high metabolic activity suggests malignancy. However, inflammatory conditions like sarcoidosis and fungal infections can also show increased uptake. These imaging tests provide clues but cannot offer a definitive diagnosis.
The only way to confirm whether the cells are benign, inflammatory, or malignant is through tissue sampling. This procedure involves obtaining a small piece of the mass for analysis by a pathologist. Common methods include bronchoscopy with endobronchial ultrasound (EBUS), where a scope is passed down the airway to guide a needle into the lymph node. Alternatively, a transthoracic needle aspiration may be performed under CT guidance, especially for masses located further from the central airways. For masses deemed low-risk or likely inflammatory, repeat imaging after a period of surveillance may be used to ensure the abnormality remains stable or resolves, supporting a benign cause.