A spot on the lung, medically known as a pulmonary nodule or mass, is a small, dense area of tissue that appears as a white shadow on a chest imaging test, such as an X-ray or Computed Tomography (CT) scan. This finding represents an opacity within the lung tissue, distinct from the surrounding healthy air-filled lung. The term is purely descriptive, indicating a physical finding on an image rather than a specific diagnosis. A nodule measures 3 centimeters (about 1.2 inches) or less in diameter; anything larger is classified as a mass. Identifying the cause requires careful evaluation, as the origin can range from harmless, healed tissue to an active disease process.
Benign Changes Caused by Scarring and Calcification
Many lung spots represent historical evidence of a past exposure or minor illness that the body successfully contained and healed. The most frequent cause of a benign nodule is the formation of a granuloma, a small cluster of immune cells. These cells form a protective wall to isolate foreign material, such as bacteria or fungal spores, preventing the spread of infection.
Over time, these clusters can undergo calcification, where calcium deposits accumulate, causing the tissue to harden. A calcified nodule indicates the spot is old and not actively growing. Scar tissue (fibrosis) from resolved pneumonia or minor lung trauma can also appear as a nodule. Since these changes are stable remnants, they remain unchanged and require no treatment.
Active Infectious and Inflammatory Conditions
A lung spot may also signify an active or recently active disease process, often driven by an ongoing infection or systemic inflammation. Tuberculosis (TB) is a notable infectious cause, where the bacteria form active lesions that appear as nodules. These lesions manifest the body’s attempt to wall off the mycobacteria, requiring immediate medical treatment.
Fungal infections, known as endemic mycoses, are another common source of active nodules, particularly in specific geographic areas. Examples include Histoplasmosis (from inhaling spores in the Mississippi or Ohio River valleys) and Coccidioidomycosis (common in the southwestern United States). These active infections require antifungal medication to clear the disease and resolve the lung spot.
Nodules can also arise from non-infectious inflammatory conditions, where the immune system mistakenly attacks the body’s own tissues. Autoimmune disorders such as Sarcoidosis or Rheumatoid Arthritis can cause inflammatory clusters of cells, called rheumatoid nodules, to form in the lungs. These spots are part of the systemic disease and may grow or shrink depending on the activity level of the underlying condition. The presence of these nodules signals a need to manage the primary inflammatory disorder.
Malignant Causes
While many lung spots are harmless, the most serious cause is a cancerous growth, which falls into two main categories: primary lung cancer and metastatic cancer. Primary lung cancer originates within the lung tissue itself, often starting as a single nodule that grows and changes over time. Risk factors like a history of smoking or exposure to substances like radon and asbestos increase the probability that a nodule is malignant.
A spot can also be caused by metastatic cancer, meaning the cancer started elsewhere (such as the colon, breast, or kidney) and spread to the lung through the bloodstream. Multiple nodules are often present in this scenario. Imaging features that raise suspicion for malignancy include a nodule size greater than 8 millimeters, rapid growth, and irregular, jagged edges (spiculation). Smooth, round nodules are generally less concerning, but any growth requires close attention.
Determining the Cause Through Diagnostic Evaluation
Once a lung spot is identified, the first step is a careful review of its size, shape, and composition on the CT scan. If the nodule is small (typically less than 6 millimeters) and the patient has no other risk factors, the standard approach is active surveillance. This involves repeating the CT scan at set intervals, such as every six to twelve months for up to two years, to check for any changes in size.
Nodules that are larger or have features suggestive of cancer, such as spiculation or a solid appearance, require more advanced testing. A Positron Emission Tomography (PET) scan is frequently used to assess the metabolic activity of the nodule. Cancer cells are typically very active and will absorb a radioactive tracer, causing the spot to “light up.” However, active infections or inflammatory conditions can also show increased activity on a PET scan.
A definitive diagnosis is ultimately achieved through tissue sampling, which involves collecting cells from the spot for examination under a microscope. This can be done via a needle biopsy, guided by a CT scan, or through a bronchoscopy, where a flexible tube is passed down the airway to the nodule. In some cases, particularly for high-suspicion nodules, surgical removal of the spot is necessary to obtain a complete diagnosis and treatment.