A lung nodule is a small, abnormal spot of dense tissue in the lung, often called a “spot on the lung.” These are common, found in up to half of all adults who undergo a chest CT scan. The vast majority of these nodules, around 95%, are benign and result from things like old infections or scar tissue. A Computed Tomography (CT) scan is the primary imaging technology used to get a detailed look at these nodules.
Why a CT Scan Is Used for Lung Nodules
A CT scan is preferred for evaluating lung nodules because it provides far more detail than a standard chest X-ray. The technology works by taking a series of X-ray images from different angles around the body and using computer processing to create cross-sectional images, or “slices,” of the lungs. This method allows a radiologist to see a nodule in three dimensions, revealing its specific size, shape, and internal composition with high precision.
This level of detail is useful for screening individuals at high risk for lung cancer with a low-dose CT (LDCT) scan to find nodules at their earliest stage. A diagnostic CT scan is also used to investigate a nodule found incidentally on another imaging test. The goal in both scenarios is to gather enough information to determine if a nodule is likely harmless or if it warrants closer monitoring or further testing.
The CT Scan Procedure
The CT scan itself is a straightforward and painless procedure. Before the scan, you will be asked to remove any metal objects, such as jewelry or glasses, that could interfere with the imaging. During the scan, you will lie on a narrow table that slides into the center of the CT scanner, which is a large, doughnut-shaped machine. The technologist will speak to you from an adjacent room and may ask you to hold your breath for a few seconds at a time to prevent blurring the images.
The process is typically quick, often completed within minutes. In some cases, a contrast material, usually an iodine-based dye, may be injected into a vein in your arm. This dye helps to highlight blood vessels and other tissues within the chest, making certain features of a nodule or surrounding structures easier to see. The decision to use contrast dye depends on what specific information your doctor is seeking from the scan.
Concerns about radiation exposure are understandable, but modern CT scanners are designed to use the lowest dose possible to achieve a clear image. For lung cancer screening, a specific low-dose CT protocol is used, which significantly reduces the amount of radiation compared to a standard diagnostic CT scan. Your medical team balances the benefits of obtaining a detailed image with the goal of minimizing radiation exposure.
Interpreting Nodule Characteristics on a CT Scan
Radiologists analyze several features of a lung nodule on a CT scan to assess its nature. Comparing the current scan to any previous imaging is a fundamental part of the evaluation, as a nodule that remains unchanged in size over a two-year period is generally considered stable and benign. Other characteristics include:
- Size: Small nodules, particularly those less than 8 millimeters, have a low probability of being cancerous. The likelihood of malignancy increases with size.
- Shape and borders: Nodules with smooth, regular borders are often benign. Those with irregular, spiculated (spiky), or lobulated (scalloped) edges are more suspicious, as these shapes can suggest the growth is infiltrating nearby lung tissue.
- Location: Nodules found in the upper lobes of the lungs may have a higher likelihood of being cancerous, though this is not a definitive rule.
- Density: Nodules can be solid, non-solid (called “ground-glass” for their hazy appearance), or part-solid, which have both a dense component and a ground-glass area.
- Calcification: The presence of calcium deposits can be a strong indicator of a benign process. Certain patterns, such as a central or popcorn-like distribution, often signify that the nodule is from a long-healed infection.
Follow-Up Actions Based on Scan Results
After a radiologist analyzes the CT scan, the findings guide the next steps, which are tailored to the individual nodule’s risk profile. If a nodule has clearly benign features, such as a specific calcification pattern or a proven history of stability over two years, the recommendation is often no further action.
For nodules that do not appear clearly benign but are considered low-risk, the most common approach is active surveillance. This involves a series of follow-up CT scans over a period of time to monitor for any changes. These scans might be scheduled at intervals of three, six, 12, or 24 months, based on established guidelines from medical organizations like the Fleischner Society. This “watchful waiting” strategy is effective for detecting any growth that might indicate a problem while avoiding more invasive procedures for the many nodules that will remain stable.
If a nodule is large or has suspicious characteristics, further evaluation may be recommended to get a more definitive answer. This could involve a Positron Emission Tomography (PET) scan, which can help determine if the nodule’s cells are metabolically active, a common feature of cancer. In other cases, a biopsy may be necessary to obtain a small tissue sample for examination under a microscope, which is the only way to confirm a diagnosis of lung cancer.