Sometimes when tissue in an organ becomes inflamed — often in response to an infection — groups of cells called histiocytes cluster to form little nodules. These little bean-shaped clusters are called granulomas.

Granulomas can form anywhere in your body but most commonly develop in your:

  • skin
  • lymph nodes
  • lungs

When granulomas first form, they’re soft. Over time, they can harden and become calcified. This means calcium is forming deposits in the granulomas. The calcium deposits make these kinds of lung granulomas more easily seen on imaging tests, such as chest X-rays or CT scans.

On a chest X-ray, some lung granulomas can look like potentially cancerous growths. However, granulomas are noncancerous and often cause no symptoms nor require any treatment.

There are seldom symptoms associated with lung granulomas themselves. However, granulomas form in response to respiratory conditions, such as sarcoidosis or histoplasmosis, so the underlying cause tends to present symptoms. These may include:

  • coughs that don’t go away
  • shortness of breath
  • chest pain
  • fever or chills

The conditions most commonly associated with lung granulomas can be divided into two categories: infections and inflammatory diseases.

Among the infections are:

Histoplasmosis

One of the most common causes of lung granulomas is a type of fungal infection known as histoplasmosis. You can develop histoplasmosis by breathing in airborne spores of a fungus normally found in bird and bat droppings.

Nontuberculous mycobacteria (NTM)

NTM, which are found naturally in water and soil, are among the more common sources of bacterial infections that lead to lung granulomas.

Some noninfectious, inflammatory conditions include:

Granulomatosis with polyangiitis (GPA)

GPA is a rare but serious inflammation of the blood vessels in your nose, throat, lungs, and kidneys. It’s unclear why this condition develops, though it appears to be an abnormal immune system reaction to an infection.

Rheumatoid arthritis (RA)

RA is another abnormal response of the immune system that leads to inflammation. RA primarily affects your joints but it can cause lung granulomas, also referred to as rheumatoid nodules or lung nodules. These granulomas are usually harmless, but there’s a small risk that a rheumatoid nodule can burst and harm your lung.

Sarcoidosis

Sarcoidosis is an inflammatory condition that most often affects your lungs and lymph nodes. It appears to be caused by an abnormal immune system response, though researchers have yet to pinpoint what triggers this response. It may be related to a bacterial or viral infection, but there’s no clear evidence yet to back up that theory.

Lung granulomas related to sarcoidosis may be harmless, but some may affect your lung function.

Because they’re small and usually cause no symptoms, granulomas are often discovered accidentally. For example, if you’re having a routine chest X-ray or CT scan because of a respiratory problem, your doctor may discover small spots on your lungs that turn out to be granulomas. If they’re calcified, they’re especially easy to see on an X-ray.

At first look, granulomas resemble possibly cancerous tumors. A CT scan can detect smaller nodules and provide a more detailed view.

Cancerous lung nodules tend to be more irregularly shaped and larger than benign granulomas, which average 8 to 10 millimeters in diameter. Nodules higher up in your lungs are also more likely to be cancerous tumors.

If your doctor sees what appears to be a small and harmless granuloma on an X-ray or CT scan, they may monitor it for a while, taking additional images over a period of years to see if it grows.

A larger granuloma may be evaluated over time using positron emission tomography (PET) scans. This type of imaging uses the injection of a radioactive substance to identify areas of inflammation or malignancy.

Your doctor may also take a biopsy of a lung granuloma to determine if it’s cancerous. A biopsy involves removing a small piece of suspicious tissue with a thin needle or a bronchoscope, a thin tube threaded down your throat and into your lungs. The tissue sample is then examined under a microscope.

Lung granulomas typically don’t require treatment, especially if you have no symptoms.

Because granulomas are usually the result of a diagnosable condition, treatment of the underlying condition is important. For example, a bacterial infection in your lungs that triggers granuloma growth should be treated with antibiotics. An inflammatory condition, such as sarcoidosis, may be treated with corticosteroids or other anti-inflammatory medications.

Once you have the underlying cause of lung granulomas under control, you may not have additional nodules form in your lungs. Some conditions, such as sarcoidosis, have no cure, but can be fairly well managed. While you may keep inflammation levels down, it’s possible more granulomas may form.

Lung granulomas and other growths in your lungs are usually identified when your doctor is looking for other respiratory problems. That means it’s important to report symptoms such as coughing, shortness of breath, and chest pain promptly to your doctor. The sooner you have symptoms evaluated and diagnosed, the sooner you can get helpful treatment.