Granulomas are nodules caused by inflammation. The inflammation may be the result of infectious or noninfectious causes. Granulomas in the lung typically do not produce any symptoms, but may be detected when a chest x-ray is done for another reason.
Infectious causes of lung granulomas
Infections are the most common cause of lung granulomas, and these infections often involve mycobacteria or fungi. Mycobacteria include tuberculosis as well as organisms that are referred to jointly as nontuberculous mycobacteria (NMT). NMT are found in water and soil.
Fungi that can lead to lung granulomas include Histoplasma, Coccidioides, and Cryptococcus. These fungi are found in soil (and sometimes in bird or bat droppings), and lung infection occurs when the spores are inhaled.   
Several other lung infections can also lead to lung granulomas, but are less common.
Non-infectious causes of lung granulomas
Sarcoidosis is the most common noninfectious cause of lung granulomas in the United States.1 The cause of sarcoidosis is unknown, but the condition causes inflammation and can lead to granulomas in any organ of the body, including the lungs. Other conditions or exposures that cause lung inflammation (such as inhaling foreign particles) can also contribute to lung granulomas.
Regardless of the underlying cause, lung granulomas are not cancerous and most do not require treatment. Treatment may be required if the condition that caused the granuloma is severe or producing symptoms.
 Mukhopadhyay S, Gal AA. Granulomatous lung disease: an approach to the differential diagnosis. Archives of Pathology & Laboratory Medicine. 2010;134:667-690.
 Centers for Disease Control and Prevention website. Histoplasmosis general information. Page last updated June 7, 2010.
 Centers for Disease Control and Prevention website. Coccidioidomycosis general information. Page last updated July 20, 2010.
 Centers for Disease Control and Prevention website. Cryptococcus (Cryptococcosis) general information. Page last updated April 28, 2010.
 National Heart Lung and Blood Institute website. What is sarcoidosis? Page last updated May 1, 2011.