A lung nodule is a small, distinct spot or growth observed in lung tissue during imaging scans. While discovering a lung nodule can be concerning, the vast majority of these findings, over 95%, are non-cancerous.
Common Causes of Lung Nodules
Lung nodules can arise from various underlying conditions, ranging from benign processes to more serious concerns. Many non-cancerous nodules result from past infections or inflammation, forming small clusters of cells called granulomas. Common examples include fungal infections like histoplasmosis or coccidioidomycosis, and bacterial infections such as tuberculosis or pneumonia.
Scar tissue from previous lung injuries or surgeries can also appear as a nodule on imaging. Additionally, certain autoimmune diseases, including rheumatoid arthritis and sarcoidosis, can cause non-infectious inflammation that leads to nodule formation. Benign tumors, such as hamartomas or adenomas, are another non-cancerous cause.
While most lung nodules are benign, some can be early indications of lung cancer or represent the spread of cancer from other parts of the body, known as metastases. Lung cancers, including non-small cell lung cancer and small cell lung cancer, can initially appear as a nodule. In such cases, the characteristics of the nodule, along with a person’s medical history, become important in determining the need for further investigation.
Assessing the Danger: Factors to Consider
Medical professionals evaluate lung nodules by considering characteristics visible on imaging and a person’s health profile. The size of a nodule is an important factor, with larger nodules raising more concern. Nodules smaller than 6 millimeters typically carry a low chance of being cancerous, while those between 6 and 8 millimeters have a slightly increased, though still low, chance. Nodules larger than 8 millimeters warrant closer evaluation due to a higher chance of malignancy, and those exceeding 30 millimeters are often classified as lung masses, which are more likely to be cancerous.
The shape and margins of a nodule provide important clues. Nodules with smooth, well-defined borders are more frequently benign. In contrast, irregular or spiky margins can indicate a higher chance of the nodule being cancerous.
Monitoring the nodule’s growth rate over time is important. Benign nodules typically remain stable in size or grow very slowly. Rapidly growing nodules are more suspicious, though very fast growth might suggest an infection rather than cancer.
The presence of calcification within a nodule is often a reassuring sign. Nodules containing calcium deposits, especially those with central, diffuse, or laminated patterns, are almost always benign, typically representing healed infections. However, irregular or eccentric calcification patterns can sometimes be associated with malignancy.
Beyond the nodule’s appearance, individual risk factors significantly influence the assessment. A history of smoking, both current and former, is the most substantial risk factor for lung cancer. Older age also increases the likelihood of a nodule being malignant. A personal or family history of cancer, particularly lung cancer, contributes to an elevated risk. Exposure to certain environmental toxins, such as asbestos or radon, can further increase this chance.
Navigating a Nodule Diagnosis
The discovery of a lung nodule often occurs incidentally during imaging performed for unrelated health issues. Once a nodule is identified, the initial approach typically involves a period of careful observation using follow-up imaging. This “watchful waiting” strategy involves repeat CT scans at regular intervals to monitor for changes in the nodule’s size or characteristics. For individuals at high risk for lung cancer, annual low-dose CT screening is recommended to detect potential cancers early.
If a nodule shows concerning features or grows during follow-up, additional diagnostic tests become necessary. A positron emission tomography (PET) scan may be performed to assess the nodule’s metabolic activity. Cancerous cells tend to be more metabolically active, helping to differentiate them from benign growths. However, a definitive diagnosis of cancer can only be confirmed through a biopsy, which involves taking a small tissue sample from the nodule for microscopic examination.
Biopsy procedures vary depending on the nodule’s location and size. Options include CT-guided needle biopsy, where a needle is inserted through the skin with imaging guidance. Bronchoscopy involves passing a thin tube with a camera down the airway to reach the nodule.
In some cases, a surgical biopsy may be performed to obtain a sample or remove the nodule entirely. If the biopsy confirms the nodule is benign, further action may not be needed beyond continued monitoring. If it is found to be malignant, early detection allows for a broader range of effective treatment options, including surgery, radiation, or chemotherapy.