More than half of all solitary pulmonary nodules are noncancerous (benign). Benign nodules have many causes, including scars and past infections.
Infectious granulomas (which are formed by cells as a reaction to a past infection) cause most benign lesions. Common infections that often result in granulomas or other healed scars include:
- Tuberculosis (TB) or exposure to TB
- Fungus, such as aspergillosis, coccidioidomycosis, cryptococcosis, or histoplasmosis
Primary lung cancer is the most common cause of cancerous (malignant) pulmonary nodules. This is cancer that starts in the lung.
A solitary pulmonary nodule itself rarely causes symptoms.
Exams and Tests
A solitary pulmonary nodule is most often found on a chest x-ray or chest CT scan. These imaging tests are often done for other symptoms or reasons.
Your doctor must decide whether the nodule in your lung is most likely benign (not cancer) or of concern. A nodule more likely benign if:
- The nodule is small, has a smooth border, and has a solid and even appearance on an x-ray or CT scan
- You are young and do not smoke
Your doctor may then choose to monitor the nodule over time by repeating a series of x-rays or CT scans.
- Repeat chest x-rays or chest CT scans are the most common way to monitor the nodule. Sometimes, lung PET scans may be done.
- If repeated x-rays show that the nodule size has not changed in 2 years, it is most likely benign and a biopsy is not needed.
Your doctor may choose to biopsy the nodule to rule out cancer if:
- You are a smoker
- You have other symptoms of lung cancer
- The nodule has grown in size or has changed when compared to earlier images
Tests to rule out TB and other infections may also be done.
Ask your doctor about the risks of having a biopsy versus monitoring the size of the nodule with regular x-rays or CT scans. Treatment may be based on the results of the biopsy or other tests.
The outlook is usually good if the nodule is benign. If the nodule does not grow larger over a 2-year period, often nothing more needs to be done.
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Update Date 8/1/2015
Updated by: Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.