Subpleural Nodules: Understanding Causes, Diagnosis, and Next Steps

Subpleural nodules are relatively common findings on chest imaging studies such as X-rays or CT scans. These small, round abnormalities located just beneath the pleura—the thin membrane lining the lungs and chest cavity—can raise concerns, but they don't always indicate a serious condition. In many cases, subpleural nodules represent benign, residual changes from previous inflammatory or infectious processes. For instance, past episodes of pleuritis, tuberculosis, or healed infections may leave behind scar-like nodular patterns that appear stable over time.

Potential Causes of Subpleural Nodules

While many subpleural nodules are harmless, it's essential to consider a range of possible underlying causes. One significant concern is metastatic disease. Cancers originating in other parts of the body—such as gastric (stomach) cancer, esophageal cancer, breast cancer, or even melanoma—can spread to the pleura and manifest as nodular lesions. These metastatic nodules often appear multiple and may grow progressively if left untreated.

Infections and Inflammatory Conditions

Infectious diseases, particularly tuberculosis (TB), remain a leading cause of pleural involvement worldwide. TB can lead to granulomatous inflammation, resulting in small nodules along the pleural surface. Other chronic infections or autoimmune conditions like rheumatoid arthritis may also contribute to pleural nodule formation, especially in patients with a relevant medical history.

Diagnostic Evaluation and Imaging

Because subpleural nodules are primarily an imaging observation, accurate diagnosis requires careful clinical correlation. A standard non-contrast CT scan of the chest is usually the first step in evaluating these nodules. However, when malignancy is suspected, a contrast-enhanced CT scan provides more detailed information about blood supply and tissue characteristics, helping differentiate between benign scars and active tumors.

In some cases, additional imaging modalities such as PET-CT may be recommended, especially if there's concern for cancer. PET scans can detect metabolic activity within nodules, offering clues about whether a lesion is likely benign or potentially malignant.

When Is a Biopsy Necessary?

Not all subpleural nodules require invasive testing. For small, well-defined, and stable nodules observed over time, a strategy of active surveillance with periodic imaging follow-up is often sufficient. However, if the nodule shows signs of growth, irregular borders, or increased metabolic activity, further investigation becomes critical. In such cases, a pleural biopsy—performed via thoracoscopy or image-guided needle techniques—may be necessary to obtain a definitive diagnosis.

Key Takeaways for Patients

Finding a subpleural nodule can be unsettling, but most are not immediately dangerous. The key is working closely with your healthcare provider to assess risk factors, review medical history, and determine the appropriate diagnostic pathway. Whether the cause is old scarring, infection, or something more serious, timely and accurate evaluation ensures the best possible outcome.