Can a CT Scan Tell if a Lung Nodule Is Cancerous?

Reviewed on 4/19/2021

No, a computed tomography (CT) scan cannot tell with certainty whether a lung nodule is cancerous. It can only indicate an abnormal spot in the lung that is opaque. This opaque spot may or may not be cancer.
No, a computed tomography (CT) scan cannot tell with certainty whether a lung nodule is cancerous. It can only indicate an abnormal spot in the lung that is opaque. This opaque spot may or may not be cancer.

No, a computed tomography (CT) scan cannot tell with certainty whether a lung nodule is cancerous. It can only indicate an abnormal spot in the lung that is opaque. This opaque spot may or may not be cancer.

The lungs are paired organs present in the chest within the rib cage that are important parts of the respiratory system. Normal lungs have a spongy texture and a pinkish-grey color. The texture, color and structure of the lungs may change due to various health conditions.

A lung nodule, also called a pulmonary nodule, is a small round or oval growth in the lung. A lung nodule may appear as a white shadow, commonly called a “spot,” on imaging studies (such as a chest X-ray or CT scan). Lung nodules are quite common and most of them are noncancerous (benign). They appear due to scarring caused by a previous infection or a benign tumor. Around 40 percent of lung nodules are cancerous (malignant). This arises due to cancer that originated in the lung (primary lung cancer) or cancer that reached the lung from another site in the body (secondary cancer metastasized to the lung). A lung nodule more than three centimeters in diameter is called a pulmonary mass.

Lung nodules are now commonly seen because of the increased use of modern imaging techniques, such as CT scans. Computed tomography, or CT scan, produces a series of images of the inside of the body. The images are taken from various angles and depths to reveal high-level detail about a certain region in the body. A CT scan does not tell whether the lung nodule is cancerous or not. It only shows that an opaque shadow or spot is present in the lungs without revealing its nature with certainty. To know whether the lung nodule is cancerous or benign, the doctor may request other tests. These typically include a positron emission tomography (PET) scan and biopsy.

If a lung nodule is seen on a CT scan, the doctor will assess the likelihood that the nodule is cancerous based on various criteria. They may advise a repeat CT scan after a few months or a year to check whether the nodule is growing. If the nodule increases in size on the repeat CT scan, the doctor may advise a PET scan. A PET scan, or positron emission tomography, may tell whether the nodule is cancer. A PET scan works based on the fact that every living cell in the body uses glucose to function. The more active the cell metabolism, the more glucose a cell will use. Since cancer cells are often metabolically far more active than normal cells, they take up more glucose. Thus, with a PET scan, a small amount of radioactive glucose is injected into a vein. The cancer cells take up a lot of this radiolabeled glucose just like they would a non-radioactive one. This makes the cancer site appear different on a PET scan compared to surrounding tissues. The increased glucose uptake, called a hot site, may also be seen in conditions affected by infections and inflammation. Hence, to confirm whether the nodule is cancer, the doctor may request a biopsy. A biopsy involves collecting a small tissue sample from the nodule and examining it under a microscope. The procedure is done under image guidance (such as a CT scan).

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References
Medscape Medical Reference

American Cancer Society


University of Rochester


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