A “spot on the lung,” often found incidentally on a chest X-ray or CT scan, usually refers to a pulmonary nodule. These small, abnormal tissue growths are frequently discovered during unrelated imaging. While investigation is required, most spots are remnants of old infections or benign scar tissue. Evaluation focuses on the spot’s characteristics and growth over time to assess risk and determine follow-up.
Understanding Pulmonary Nodules and Masses
The initial assessment depends heavily on size, which dictates the terminology. A pulmonary nodule is defined as an opacity measuring up to three centimeters in diameter. Lesions larger than three centimeters are classified as a pulmonary mass, which has a higher probability of being malignant.
Radiologists analyze the nodule’s internal structure and borders using a CT scan. Nodules are categorized as solid, subsolid (ground-glass or part-solid), or calcified (containing calcium deposits). Benign calcification patterns—such as diffuse, central, laminated, or “popcorn” shapes—strongly suggest a non-cancerous origin, often from a healed infection.
The nodule’s margin appearance is indicative of its nature. Smooth, well-defined borders are typically benign. Irregular, jagged, or spiculated (spiky) margins raise suspicion for malignancy. Location is also considered; upper lobe nodules are sometimes associated with a slightly higher risk. These characteristics guide the physician in estimating the likelihood of a benign versus malignant cause.
Categorizing the Potential Causes
Pulmonary nodules and masses are categorized as benign or malignant, with benign causes being more common. The most frequent benign cause is a granuloma, a small cluster of inflammatory cells that forms when the body walls off a past infection. These often result from exposure to fungal diseases (like histoplasmosis or coccidioidomycosis) or healed bacterial infections (like tuberculosis).
Other non-cancerous causes include localized scar tissue, known as fibrosis, resulting from prior inflammation or injury. Less common but non-threatening causes include benign tumors, such as hamartomas. Autoimmune conditions, including rheumatoid arthritis and sarcoidosis, can also create inflammatory nodules.
Malignancy is the most serious potential cause, arising either as primary lung cancer or as metastatic cancer spread from a tumor elsewhere in the body. The risk of a nodule being cancerous correlates closely with its size. Those smaller than six millimeters have less than a one percent chance of malignancy, while the probability rises sharply for nodules over 20 millimeters. A rapid increase in size—a doubling of volume between one month and one year—is a strong indicator of a malignant process.
The Evaluation and Monitoring Process
Once a pulmonary nodule is identified, evaluation is guided by medical protocols. A high-resolution CT scan is the standard tool used to analyze the nodule’s size, shape, and internal features, determining the patient’s risk profile. If the nodule is stable and displays benign characteristics, such as dense, uniform calcification, no further follow-up is necessary.
For small nodules that are not clearly benign, physicians employ a surveillance strategy involving serial low-dose CT scans over a specified period. This monitoring, often based on guidelines from organizations like the Fleischner Society, tracks changes in the nodule’s size or appearance. A nodule that remains unchanged for two years is likely benign and requires no further intervention.
If a nodule is larger than eight millimeters or has suspicious features, a Positron Emission Tomography (PET) scan may assess its metabolic activity. Malignant cells are highly active and consume more glucose, causing the nodule to “light up” on the PET scan. This refines the risk estimate before moving to an invasive procedure.
If the risk of malignancy remains high, a biopsy is necessary for a definitive diagnosis. This involves a needle aspiration guided by imaging or a surgical procedure to remove a tissue sample or the entire nodule. The decision to perform an invasive procedure is weighed against the patient’s overall health and potential complications.