Lung Shadow on Chest X-Ray

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Lung Shadow on Chest X-Ray

Question:

My chest X-ray shows a small shadow on one of my lungs. I had pneumonia 18 years ago with a lot of scarring. Could this be what the shadow is?

Answer:

Air takes up almost all of the space in your lungs, and air shows up on chest X-rays and computed tomography scans (CT or "CAT" scans) as dark patches. If you have a gray or white "spot" or "shadow" on your X-ray or CT scan, it can be caused by a variety of different things.

Scarring from prior pneumonia is one possible explanation. Some "shadows" on an X-ray are normal parts of anatomy, such as breasts. A shadow might even come from a fold in a hospital gown you were wearing at the time of your X-ray.

A spot in the lung that has distinct edges is also called a "solitary pulmonary nodule" or in some cases, a "coin lesion."

When a nodule is seen on a chest X-ray, one concern is that it may be cancer. In one report of about 60 nodules that were 1 centimeter in size or smaller, cancer was the cause of about half of the nodules.

Several other common things can cause nodules in the lung. The first is inflammation from an infection or other irritation in the lung. A fungal infection (for example, infection with the fungus Cryptococcus) can cause mild or unnoticeable symptoms. This infection can create a nodule in your lung as your immune system "walls off" the infection into a small solid capsule. Solitary pulmonary nodules can be caused by diseases that result in inflammation, such as rheumatoid arthritis or sarcoidosis. A nodule also can form during the bruising and healing that can be caused by a chest injury.

A lung nodule can be a benign growth. The most common benign growth in lungs is called a hamartoma. A hamartoma is a clump of tissue containing a variety of normal lung cells, but the cells are not organized into tubes and air sacs like a normal segment of your lung, so they can't fill with air. A second benign growth that can occur in the lung is a hemangioma, a cluster of small arteries.

Most lymph nodes in your chest are grouped next to the trachea and large blood vessels in the center of your thorax, between your two lungs. Occasionally, however, a lymph node can be located away from the center, within one of your lungs. In this case, a lymph node can definitely appear on X-rays as a solitary pulmonary nodule.

Mary Pickett, M.D., is a lecturer for Harvard Medical School and an assistant professor of medicine at Oregon Health & Science University in Portland, OR. At OHSU, she practices general internal medicine and teaches medical residents and students.

Last updated:	July 20, 2009