What are pulmonary nodules?
A pulmonary nodule is a small round or oval-shaped growth in the lung. It may also be called a “spot on the lung” or a “coin lesion.” Pulmonary nodules are smaller than three centimeters (around 1.2 inches) in diameter. If the growth is larger than that, it is called a pulmonary mass and is more likely to represent a cancer than a nodule.
How common are pulmonary nodules?
Countless pulmonary nodules are discovered each year during chest X-rays or CT scans. Most nodules are noncancerous (benign). A solitary pulmonary nodule is found on up to 0.2% of all chest X-rays films. Lung nodules can be found on up to half of all lung CT scans. Risk factors for malignant pulmonary nodules include a history of smoking and older age.
Symptoms and Causes
What causes pulmonary nodules?
There are two main types of pulmonary nodules: malignant (cancerous) and benign (noncancerous). Over 90% of pulmonary nodules that are smaller than two centimeters (around 3/4 inch) in diameter are benign.
Benign pulmonary nodules can have a wide variety of causes. Many are the result of inflammation in the lung as a result of an infection or disease producing inflammation in the body. The nodule may represent an active process or be the result of scar tissue formation related to prior inflammation. Benign developmental lesions may also appear as nodules.
- Infections— Most infections that appear as with pulmonary nodules are relatively indolent and often not active. Examples include mycobacterium such as mycobacterium tuberculosis or mycobacterium avium intracellulare, and fungal infections such as aspergillosis, histoplasmosis, coccidiomycosis, and cryptococcosis. Inflammation related to infections often forms what is termed a granuloma. A granuloma is a small clump of cells that form when lung tissue becomes inflamed. Granulomas form when the immune system isolates substances that it considers foreign. Most of the time granulomas occur in the lungs, but they may also form in other parts of the body. They can become calcified over time, as calcium tends to collect in the healing tissue
- Noninfectious causes of benign inflammatory lung nodules—Noninfectious disorders such as sarcoidosis, granulomatosis with polyangiitis (GPA), and rheumatoid arthritis also show themselves with granulomas forming in the lungs
- Neoplasms—Neoplasms are abnormal growths that may be benign or malignant. Types of benign neoplasms include:
- Fibroma (a lump of fibrous connective tissue)
- Hamartoma (an abnormal grouping of normal tissues)
- Neurofibroma (a lump made up of nerve tissue)
- Blastoma (a growth made up of immature cells)
- Types of malignant tumors include:
- Lung cancer
- Lymphoma (a growth containing lymphoid tissue)
- Carcinoid (a small, slow-growing cancerous tumor)
- Sarcoma (a tumor consisting of connective tissue)
- Metastatic tumors (tumors that have spread to the lungs from cancer in another part of the body)
What are the symptoms of pulmonary nodules?
Usually there are no symptoms associated with pulmonary nodules. If present, symptoms would be related to the condition that led to the nodule developing. If the nodule is from a lung cancer, the patient is often without symptoms but may have a new cough, or cough up blood.
Most of the time, a patient is unaware that he or she has a lung nodule until a chest X-ray or computed tomography scan (CT scan) of the lungs is performed.
Diagnosis and Tests
How is the cause of pulmonary nodules diagnosed?
Though most lung nodules are not malignant, it is very important that those representing cancer are identified early in their course, when they are curable.
Chest X-rays and CT scans: Usually, the first sign that a pulmonary nodule is present is a spot on the lung that shows up on a chest X-ray or a CT scan. These tests are usually done when a person sees the doctor for a respiratory illness.
If the X-ray film or CT scan indicates there is a pulmonary nodule, your doctor will ask you about your medical history, including whether you have had cancer in the past. He or she will want to know whether you are a smoker or former smoker and about any exposure to environmental chemicals that may be toxic.
The doctor will look at the X-ray to evaluate the size and shape of the nodule, its location, and its general appearance. Single pulmonary nodules seen on chest x-rays are generally at least 8 to 10 millimeters in diameter. If they are smaller than that, they are unlikely to be visible on a chest X-ray. The larger the nodule is, and the more irregularly shaped it is, the more likely it is to be cancerous. Those located in the upper portions of the lung are also more likely to be cancerous.
If you have any older chest X-rays, you should let your doctor look at them to determine the growth rate of the nodule. In general, malignant nodules double in size every one to six months. Nodules with a slower or faster growth rate are less likely to be cancerous.
Your doctor may recommend that you undergo a CT scan to obtain a more detailed image of the nodule, or your nodule may have first been identified by a CT scan. CT scans can give information about the specific features of the nodule, including its shape, size, location and internal density. CT scans are more accurate than chest x-rays in determining the nature of the nodule. A CT scan can find very small nodules, as small as 1-2 mm in diameter.
If the nodule is small enough or if its features suggest a very low likelihood that it represents a cancer, your doctor is likely to follow the nodule over time with repeated chest imaging. If the nodule does not grow over time, it is confirmed to be benign. If a concerning pace of growth is noted, then additional evaluation would be suggested. The interval between scans and the length of follow-up depends on the size of the nodule and the risk of malignancy.
Positron emission tomography (PET): A PET scan can also help to find out if a nodule is malignant or benign. A PET scan uses a radiolabeled substance such as glucose that is absorbed by the nodule, and provides a picture of the nodule’s metabolic activity level. Malignant cells have faster metabolic rates than normal cells, so they require more energy and thus absorb more of the radiolabeled substance. Nodules can light up on PET imaging if they are malignant or if there is active inflammation. We have to be careful with the PET scan interpretation when someone has nodules smaller than 8-10 mm because they are not seen well by PET imaging.
Biopsy: A biopsy is a procedure in which a small tissue sample is removed from the nodule so it can be examined under a microscope. It may be performed when other tests are inconclusive to rule out the chance that a growth is malignant.
There are two ways, short of going through surgery, to collect samples from lung tissue. The method used depends on the size and location of the nodule, as well as the comfort of the medical team with these procedures.
- Bronchoscopy: This procedure is used if it appears the nodule can be reached through the breathing tubes. It uses a bronchoscope, which is a thin, lighted flexible tube that can be inserted into the mouth or nose and through the windpipe (trachea) into the bronchus (airway) of the lung. The bronchoscope has a very small camera at its end. Biopsy tools can be passed through the camera to reach the nodule.
- Needle biopsy (also known as transthoracic needle aspiration): This test is most successful when the nodule is towards the edge of the lung, near the chest wall. A needle is inserted through the chest wall and into the nodule, usually under the guidance of a CT scan.
If the nodule has a very concerning appearance or growth pattern, or it is somewhat concerning and its nature is not able to be clarified by the above tests, the best step may be to remove the nodule. This will clarify its nature while treating it. This requires the patient be fit enough to undergo the surgery.
Management and Treatment
How are pulmonary nodules treated?
If the pulmonary nodule is benign, it usually does not require treatment. If an active infection is found or a disease of inflammation in the body is diagnosed, the treatment would be based on the condition identified and the symptoms that are present.
If the nodule is malignant, there does not appear to be any spread of the cancer, and the patient is fit, then the cancer should be surgically removed. If a non-surgical biopsy of a nodule with high concern for malignancy is done and the results are inconclusive, it is recommended that the nodule be taken out.
Surgical techniques to take out pulmonary nodules include:
- Thoracotomy: This procedure is considered open lung surgery. A cut is made in the wall of the chest in order to remove pieces of diseased lung tissue. Patients usually have to remain in the hospital for a few days after the operation. The mortality risk is low. When possible, a mini-thoracotomy that is less invasive may be performed
- Video-Assisted Thoracoscopy: This procedure uses a thorascope, a flexible tube with a miniature camera on its end. The thorascope is inserted through a small cut into the chest wall. The camera allows the surgeon to view an image of the nodule on a television screen. This technique requires a smaller cut and a shorter recovery time than a thoracotomy does
How can malignant pulmonary nodules be prevented?
The best way to avoid getting a malignant pulmonary nodule is to quit smoking if you are a smoker.