A lung nodule is a small spot or growth in the lung, often detected incidentally during medical imaging. While finding one can be concerning, most are not cancerous and do not pose a serious threat. These nodules frequently require further investigation to determine their nature.
What Exactly Are Lung Nodules?
A lung nodule, also known as a pulmonary nodule, is a small, rounded or oval growth within the lung tissue. These growths are typically defined as being less than 3 centimeters (about 1.2 inches) in diameter. If a growth is larger than 3 centimeters, it is generally classified as a “mass” and is viewed with greater suspicion for malignancy.
Lung nodules are frequently discovered by chance during chest X-rays or CT scans performed for unrelated medical reasons, such as an injury or a routine check-up. A nodule itself is a finding on an image, not a definitive diagnosis, indicating the need for additional evaluation to understand its cause.
Non-Cancerous Causes
Many factors can lead to the formation of non-cancerous lung nodules. These benign nodules are more common than cancerous ones.
Previous or ongoing infections are a frequent cause, as they can leave behind scar tissue or small collections of immune cells called granulomas. Fungal infections like histoplasmosis, coccidioidomycosis (Valley Fever), and blastomycosis are common culprits, as are bacterial infections such as tuberculosis.
Inflammatory processes can also cause lung nodules. These may be linked to autoimmune diseases where the body’s immune system mistakenly attacks its own tissues. Conditions like rheumatoid arthritis, sarcoidosis, and granulomatosis with polyangiitis can manifest with lung nodules.
Benign tumors, such as hamartomas, are another non-cancerous cause. These are common benign lung tumors composed of disorganized but normal lung tissues like cartilage, fat, and connective tissue. Additionally, old injuries or prior lung conditions can result in stable scar tissue that appears as a nodule on imaging.
Cancerous Causes
While many lung nodules are benign, some can indicate the presence of cancer. Understanding these causes is important for proper evaluation.
A lung nodule can be an early sign of primary lung cancer, which originates in the lung tissue itself. Detecting lung cancer at this early stage, when it appears as a nodule, can significantly improve treatment outcomes. Nodules that are larger, have irregular or spiky shapes, or grow quickly are more likely to be cancerous.
Cancer from other parts of the body can also spread to the lungs, forming metastatic nodules. Cancers of the colon, breast, kidney, or melanoma are examples that commonly spread to the lungs. These metastatic nodules are often multiple, but sometimes only a single nodule may be present. Factors that increase the likelihood of a nodule being cancerous include a history of smoking, older age, and previous cancer diagnoses.
How Doctors Investigate Lung Nodules
Medical professionals follow a structured approach to investigate lung nodules and determine their cause. This process involves considering several factors.
Doctors first gather a detailed patient history, including age, smoking status, family history of cancer, and any past medical conditions or travel history that might suggest an infection. The characteristics of the nodule on imaging scans, such as its size, shape, borders, density, and whether it has calcifications, are also carefully evaluated. Comparing new scans with any older imaging studies helps determine if the nodule has changed over time.
Often, the initial step after detecting a nodule is a period of imaging follow-up, typically with repeat CT scans at intervals like 3, 6, or 12 months. This monitors for growth or other changes. If the nodule appears suspicious or shows changes during follow-up, further diagnostic tests may be recommended. These can include a PET scan to assess the nodule’s metabolic activity, as cancerous cells often show increased activity.
If a definitive diagnosis is still needed, a biopsy may be performed to obtain tissue for microscopic examination. Biopsy methods include needle biopsy or bronchoscopy, where a thin tube with a camera is used to reach the nodule. In some cases, surgical removal of the nodule may be necessary for diagnosis.