Lung nodules are common findings on chest imaging, appearing as small spots or lesions within the lung tissue. While they can cause concern, most lung nodules are not cancerous. Understanding their appearance on a CT scan helps clarify their nature and guide next steps. This article explores the visual characteristics of lung nodules on scans and how these features are interpreted.
Understanding Lung Nodules
A lung nodule is a small, round or oval-shaped growth in the lung, typically less than 3 centimeters (about 1.2 inches) in diameter. Growths larger than 3 centimeters are classified as a lung “mass,” which has distinct implications.
Lung nodules are frequently discovered incidentally during CT scans for unrelated symptoms or as part of lung cancer screening. They appear in approximately one out of every three chest CT scans. Most lung nodules are benign, meaning they are non-cancerous.
How Lung Nodules Appear on Scans
Computed tomography (CT) scans provide detailed views of lung nodules, allowing observation of specific visual characteristics. These features include the nodule’s size, shape, borders, and internal density or composition. CT scans are significantly more sensitive than standard X-rays for detecting and characterizing these small growths.
Nodule size is measured in millimeters; even very small nodules can be detected. Nodules can appear in various shapes, such as round or oval, with borders that are smooth, lobulated (bumpy), or spiculated (spiky or jagged). Internal density is also important, with categories including solid, subsolid, and calcified. Subsolid nodules can be ground-glass opacity (hazy like frosted glass) or part-solid (containing both hazy and solid components).
Interpreting Nodule Features
A lung nodule’s visual characteristics on a CT scan offer important clues about its nature, helping assess the likelihood of it being benign or malignant. Size is a significant factor; smaller nodules (under 6 millimeters) generally have a very low probability of being cancerous (typically less than 1%). As the size increases, the risk of malignancy tends to rise.
Shape and margins also provide insights. Nodules with smooth or rounded borders are more often benign, while irregular, lobulated, or spiculated (spiky) margins raise more concern for malignancy. Spiculated margins are highly suggestive of certain types of cancer.
Calcification within a nodule, appearing as bright white spots, often indicates a benign cause like a healed infection or inflammation. However, some malignant nodules can also show calcification, usually in different patterns. Changes in a nodule’s size over time are closely monitored, as growth can suggest malignancy, while stability over two years generally indicates a benign nature.
What Happens After Nodule Discovery
Once a lung nodule is identified and assessed, next steps depend on its characteristics and the patient’s individual risk factors. Since most lung nodules are benign, watchful waiting is a common approach, involving active surveillance through serial CT scans. Follow-up scan timing varies based on nodule size and appearance; smaller, low-risk nodules often require less frequent monitoring, such as annually.
Larger nodules or those with concerning features may require more frequent CT scans (e.g., every 3 to 6 months) to monitor for changes. Further imaging, like a PET (positron emission tomography) scan, might evaluate the nodule’s metabolic activity to differentiate between benign and active cancerous growths. If the nodule exhibits concerning features or shows growth, a biopsy may be performed to obtain a tissue sample for microscopic examination. This is the only definitive way to diagnose cancer.
Management decisions are often made collaboratively by a multidisciplinary team, including radiologists, pulmonologists, and thoracic surgeons.