Lung nodules are described as "spots" that are 3 centimetres (1.5 inches) in diameter or less. These nodules are often referred as coin lesions. Lesions larger than 3 cm
are referred as lung masses which are more likely to be cancerous. Lung nodules usually need to be at least one centimetre in size before they can be seen on a chest x-ray,
whereas nodules as small as one to two millimetres may sometimes be seen on a CT scan.
Factors such as a history of smoking,
what the nodule looks like (for example, if calcifications
are present), and more may help in assessing whether the nodule is malignant or benign. Diagnosis usually includes a CT scan or other studies, but a biopsy is needed to make a
conclusive diagnosis. Treatments will vary depending on the specific cause of the nodule.
At least 60 percent of lung nodules overall—are not cancerous and that if a nodule is lung
cancer there is still a good chance that it can be cured. A nodule, by definition, is less than three centimetres in diameter, and at this size, many lung cancers are curable.
Yet even for lung cancers that are larger, the treatment and survival rates for lung cancer have improved significantly in just the past few years.
At the current time, there are more former smokers and never smokers who develop lung cancer, than people who smoke. Anyone who has lungs can get lung cancer, and in fact, lung cancer has
been significantly increasing among one group: young, never-smoking women.
Most lung nodules do not cause any symptoms and are found “accidentally” or "incidentally" when a chest x-ray is done for some other reason. If symptoms are present, they may include a cough, coughing up blood, wheezing, shortness of breath (often vague at first and only with activity), or respiratory infections if the nodule(s) is located near a major airway.
Lung nodules can be either benign (non-cancerous) or malignant (cancer). The most common causes overall include granulomas (clumps of inflamed tissue due to an infection or inflammation) and hamartomas (benign lung tumours). The most common cause of malignant lung nodules includes lung cancer or cancers from other regions of the body that have spread to the lungs (metastatic cancer). Recent research suggests that even when a lung nodule is found in a person who might be expected to have lung metastases, only half of the nodules were metastases when biopsied. Up to 25 percent, rather, were a second primary lung cancer.
Nodules can be broken down into a few major categories.
Infections: Infectious causes of nodules may include bacterial infections such as tuberculosis and
other mycobacterial infections, fungal infections such as histoplasmosis, blastomycosis, aspergillosis, and coccidiomycosis,
and parasitic infections such as ascariasis (roundworms), echinococcus (hydatid cysts), and paragonimous (liver flukes).
When the immune system "walls off" areas of infection it often forms granulomas.
Inflammation: Conditions such as rheumatoid arthritis, sarcoidosis, and Wegener's granulomatosis,
as well as pneumoconioses such as silicosis can also lead to granulomas.
Benign tumours: Benign lung tumours such as hamartomas (the most common benign lung tumour), bronchial adenomas,
fibromas, blastomas, neurofibromas, and haemangiomas. can show up as a nodule in the lungs on x-ray.
Malignant tumours: Cancers that may appear as a nodule includes lung cancer, lymphomas, sarcomas, and carcinoid tumours
Metastases: Lung nodules may also be due to metastases from other cancers such as breast cancer,
colon cancer, bladder cancer, and prostate cancer. When a nodule is due to a metastasis from another cancer, there are
often multiple lung nodules present.
Other benign nodules: Pulmonary infarctions (areas of lung tissue that have lost their blood supply), blood vessel
abnormalities (AV malformations), atelectasis (collapse of part of a lung), pulmonary fibrosis, and amyloidosis are all other
possible causes of a lung nodule.
The first thing is to obtain any previous x-rays you may have had and compare them. If the nodule or nodules have been present for a long time,
further tests may not be needed. If the nodule is new or there are no prior x-rays to compare, further workup may be needed.
If a nodule is found on a chest x-ray, the first step is usually to do a CT scan of your chest. The history as well as any risk factors for any type of lung nodules.
For example, if there is a recent travel history, a fungal infection may be likely, whereas if you have smoked, a malignant tumour may be more likely.
Characteristics of the tumour as seen on your CT scan will also be evaluated.
A PET scan is sometimes helpful in further defining a nodule. Unlike CT scans which are "structural" tests, a PET scan is a "functional test." A CT scan can find lesions in the
lungs but does not give a measure of what is happening in a nodule. With a PET scan, a small amount of radioactive sugar is injected into the blood stream.
Actively growing tumours take up more of the sugar which lights up on the examination. This can be helpful in distinguishing a growing tumour from a scar
tissue as a growing tumour will take up more of the sugar. This is especially helpful for those who have had previous chest radiation, lung infections, or
surgery which may result in scar tissue.
If a nodule does not appear to be growing or has characteristics of a benign tumour, (has "low probability" of being cancer) a "wait and watch" approach
may sometimes be taken, with a CT scan repeated after a certain period of time. Single solitary nodules that have remained unchanged for a period of two
or more years do not generally need any further workup.
Biopsy of Pulmonary Nodules
Unfortunately, a lung biopsy is often needed to know for sure what is causing a nodule. Thankfully, newer and less invasive methods of sampling tissue are now
often available. Depending on the location of the nodule, a fine needle biopsy may be done. The biopsy can be done as part of a bronchoscopy or a CT
guided through the chest wall. At times an open biopsy may be needed. Even when this is the case, newer techniques, such as video-assisted thoracoscopic
surgery (VATS) can often be done instead of a thoracotomy.
Benign vs. Malignant Nodules
Overall, the likelihood that a lung nodule is cancer is 40 percent, but the risk of a lung nodule being cancerous varies considerably depending on several factors.
In people less than 35 years of age, the chance that a lung nodule is cancer is less than one percent, whereas half of lung nodules in people over age
50 are malignant (cancerous).
Other factors that raise or lower the risk that a lung nodule is cancer include:
Indeterminate Lung Nodules
- Size: Larger nodules are more likely to be cancerous than smaller ones.
- Smoking: Current and former smokers are more likely to have cancerous lung nodules than never smokers.
- Occupation: Some occupational exposures raise the likelihood that a nodule is cancer.
- Medical history: Having a history of cancer increases the chance that a nodule could be malignant.
- Family history: Those who have nodules and a family history of lung cancer are more likely to have cancerous nodules than those without a family history.
- Symptoms: The chance that a nodule is lung cancer is greater if other signs or symptoms of lung cancer are present.
- Shape/appearance of the nodule: Smooth, round nodules are more likely to be benign, whereas “spiculated” nodules, or those with irregular or lobular borders are more likely to be cancerous.
- Solid/non-solid: Nodules that are part solid rather than solid are more likely to be cancerous
- Growth: Cancerous lung nodules tend to grow fairly rapidly with an average doubling time of about four months, while benign nodules tend to remain the same size over time.
- Calcification: Lung nodules that are calcified are more likely to be benign.
- Cavitation: Nodules described as “cavitary,” meaning that the interior part of the nodule appears darker on x-rays, are more likely to be benign.
- Ground glass nodules: Nodules that are described as having a ground glass appearance are often a challenge and can be either benign or malignant. Due to this difficulty, a biopsy of these lesions is usually needed.
- The number of nodules: Those who have multiple lung nodules are more likely to have cancer than those who have a solitary or only a few pulmonary nodules. The most common cause of multiple lung nodules is metastatic cancer from the breast, prostate, colon, or bladder (though many tumours can metastasize to the lungs).
- Location of the nodules: Lobules located in the right or left lower lobes or the right middle lobe of the lung are less likely to be cancerous than those located in the left or right upper lobes.
- Ethnicity and geographic location: If there is a travel history or a long stay overseas, a lung nodule may be benign. For example, recent studies have found that lung nodules due to schistosomiasis, a parasitic infection, are fairly common in Africans. Likewise, nodules related to fungal infections, such as coccidiomycosis.
The number of lung nodules that are read by radiologists as "indeterminate" has increased with the advent of lung cancer screening.
Hearing that the nodule or nodules are indeterminate can be confusing. Unfortunately, there are times when it is impossible on imaging
tests alone to know whether a nodule is malignant—even after considering all of the factors above. In order to answer this question, a
biopsy must be done.
Lung Cancer Screening
Lung cancer screening in appropriate people has been found to decrease the mortality rate from lung cancer by 20 percent. But as with
any screening test, there is the risk of false positives, and it's common to find nodules on CT screening. But finding nodules does not
always mean cancer. In fact, studies thus far estimate that only around five percent of nodules found on a first lung CT screening are cancerous.
The treatment of lung nodules varies widely depending upon the cause, whether they are related to infections, inflammation, cancer, or other conditions.
Most benign lung nodules, especially those that are present and have not changed over a period of a few years, can be left alone.
Worried about Lung Nodules?