A granuloma is a small area of inflammation in tissue. Granulomas are most often the result of an infection and most frequently occur in the lungs, but can occur in other parts of the body as well. They typically cause no signs or symptoms and are found incidentally on a chest X-ray done for some other reason.
The most common cause of lung granulomas in the United States is histoplasmosis, a fungal infection that primarily affects the lungs. People who acquire pulmonary histoplasmosis that results in a lung granuloma have almost always spent some time in the Ohio Valley or the upper Midwest. Most people with pulmonary histoplasmosis never suspect they have the disease because signs and symptoms are rare.
Although granulomas due to histoplasmosis are noncancerous (benign), they may resemble cancer on an X-ray, especially if they haven't calcified — over time, granulomas become calcified and have the same density as bone, making them more clearly visible on an X-ray.
A doctor may make a diagnosis of granuloma by chest X-ray or, if the granuloma is not apparently calcified, by computerized tomography (CT), which can detect the calcium that isn't evident on the chest X-ray. The images of affected tissue usually show scarring and calcification characteristic of a granuloma. Granulomas almost never require treatment or even follow-up chest X-rays.