Discovering a spot on a lung scan can cause significant anxiety due to the possibility of cancer. Lung nodules, often called “spots on the lung,” are common findings on chest imaging, such as a computed tomography (CT) scan. These small, rounded areas of tissue are typically remnants of past inflammation or infection, and the vast majority are not cancerous. Understanding what a lung nodule is and how doctors assess its risk can provide clarity and reassurance.
What Exactly Is a Lung Nodule?
A lung nodule, or pulmonary nodule, is a small, focal density in the lung tissue that appears as a white shadow on an imaging scan. A nodule is defined as a growth measuring 3 centimeters (about 1.25 inches) or less; anything larger is classified as a mass and is treated with higher suspicion for malignancy. Nodules are frequently caused by benign conditions, such as a granuloma (scar tissue formed after a healed fungal or bacterial infection like tuberculosis), inflammatory diseases, benign tumors, or scarring from old injuries.
Nodules are categorized by their appearance on the CT scan to help determine risk. A solid nodule is dense throughout, while a non-solid or ground-glass nodule appears hazy. Part-solid nodules contain both a hazy component and a dense component, and this mixed composition is often associated with a higher likelihood of slow-growing malignancy.
General Statistics on Malignancy
Approximately 95% of all pulmonary nodules identified are benign. For nodules smaller than 6 millimeters, the probability of them being malignant is less than 1%, even in patients at high risk for lung cancer. This low rate is consistent whether the nodule is found incidentally or during a dedicated screening program.
The risk profile shifts depending on the population studied. For example, in high-risk individuals undergoing low-dose CT lung cancer screening, the incidence of lung cancer among detected nodules is higher, historically around 1% to 4%. This difference highlights the importance of individual risk assessment, as the clinical context of the finding affects its interpretation.
Key Factors Increasing Cancer Risk
A nodule’s risk of being cancerous is determined by a combination of a patient’s clinical history and the nodule’s specific characteristics on imaging.
Patient Factors
Patient factors that elevate risk include older age, a substantial history of heavy smoking (measured in pack-years), a personal history of another type of cancer, and exposure to environmental toxins like asbestos or radon. A family history of lung cancer also increases suspicion.
Nodule Characteristics
The nodule’s physical appearance and behavior are equally important. Larger nodules carry a greater risk, with solid nodules 8 millimeters or more demanding aggressive evaluation. The shape of the borders also provides a clue; benign nodules often have smooth, well-defined margins, while malignant nodules frequently display irregular or jagged edges, sometimes described as spiculated.
The nodule’s growth rate over time is one of the most informative features. Cancerous nodules typically exhibit a volume doubling time between one month and one year. Nodules that remain stable in size for two years or longer are highly likely to be benign and require no further follow-up. Subsolid nodules, particularly those with a growing solid component, are associated with a higher risk of malignancy and are monitored for longer periods due to their slow-growing nature.
How Doctors Manage and Monitor Nodules
The management strategy for a newly discovered lung nodule is individualized based on the estimated probability of malignancy, combining the patient’s risk factors with the nodule’s imaging characteristics. For the smallest, lowest-risk nodules (typically under 6 millimeters), no routine follow-up may be necessary. For nodules posing a low to intermediate risk, the standard approach is active surveillance through repeat low-dose CT scans.
The timing of follow-up scans is structured to detect concerning growth while avoiding unnecessary procedures. For solid nodules between 6 and 8 millimeters, a repeat CT scan is often recommended in six to twelve months to check for stability. If a nodule is new, growing, or larger than 8 millimeters with suspicious features, further advanced imaging or an invasive procedure is considered.
A positron emission tomography (PET) scan may be used for higher-risk solid nodules to assess metabolic activity, as malignant cells show high glucose uptake. If the risk remains high after imaging, a definitive diagnosis requires a biopsy or surgical removal of the nodule. This structured monitoring aims to safely identify malignant nodules at the earliest stage while avoiding invasive testing for benign findings.