Lung Nodule Causes, Symptoms, and Treatment

Lung nodules are small lesions in the lung that can be seen on an X-ray or CT scan. Lung nodule causes include infection, inflammation, and scarring. Less commonly, they can be caused by a more serious condition such as lung cancer. 

Most lung nodules are not cancerous. However, it’s essential to follow through on getting a diagnosis, even if you’ve never smoked.

This article will explain what causes lung nodules, how they are diagnosed, the risk of your lung nodule being cancerous, and how they are treated.

What Is a Lung Nodule?

Lung nodules look like spots on X-rays and CT scans. They are sometimes also referred to as "coin lesions" because they often have a round, coin-like shape.

Lung nodules are defined as being 3 centimeters (cm) or 1.2 inches in diameter or less. They need to be at least 1 cm in size before they can be seen on a chest X-ray. CT scans provide more finely detailed images and can detect nodules as small as 1 to 2 millimeters. 

Symptoms of Lung Nodules

Lung nodules are so small that they don't tend to cause breathing problems or other symptoms. That's why they're usually found 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 mild at first and only with activity
• Respiratory infections, especially if the nodule is located near a major airway

Lung Nodule Causes

Lung nodules can be benign (noncancerous) or malignant (cancerous). Most benign lung nodules result from inflammation due to infections or illnesses.

When your lungs become inflamed, tiny masses of tissue can develop.  Over time, the clumps can harden into a nodule on your lung.

The causes of most benign lung nodules include:

• Infections, including bacterial infections such as tuberculosis and pneumonia; fungal infections from inhaling spores found in bird or bat droppings, or moist soil, wood, and leaves; and parasitic infections such as roundworms and tapeworms
• Inflammation from irritants in the air, air pollution, or autoimmune conditions such as rheumatoid arthritis or sarcoidosis
• Scarring from surgery, chest radiation, or previous infection

Other, less-common causes of a lung nodule include:

• Pulmonary infarctions: Areas of lung tissue that have lost their blood supply
• Arteriovenous malformations: A type of blood vessel abnormality
• Atelectasis: Collapse of part of a lung
• Pulmonary fibrosis: Thickening, scarring of lung tissue
• Amyloidosis: Build-up of a kind of protein in the lung

The most common causes of malignant lung nodules are primary lung cancer that started in the lung or metastatic cancers from other regions of the body that have spread to the lungs.

• Malignant tumors: Cancers that are often first detected as nodules include lung cancer, lymphomas, and sarcomas
• Metastases: Breast cancer, colon cancer, bladder cancer, prostate cancer, and other cancers can spread to the lungs; when a nodule is due to metastasis from another cancer, there are often multiple lung nodules present

Carcinoid tumors, a kind of neuroendocrine tumor, are usually benign tumors except in rare cases when the tumor is metabolically active and called malignant carcinoid. 

Risk Factors

Some illnesses you may have had and lifestyle factors may increase your risk of having lung nodules. Some of these include:

• Active or past smoker
• Exposure to secondhand smoke
• History of tuberculosis, pneumonia, surgery, or chest radiation
• Age 65 or older
• Exposure to asbestos or radon
• Received radiation therapy in the past
• Working in an occupation that exposes you to certain chemicals
• Family history of cancer

Certain environmental conditions can also predispose you to getting lung nodules. If you live in the southwest or have traveled to certain countries, a fungal or parasitic infection may be considered as the potential cause of your lung nodule.

Where you live, work, and have traveled can play a role, too. For example, if you work outdoors with moist wood or soil, your lung nodules may be caused by a fungal or parasitic infection.

Studies have found that lung nodules due to schistosomiasis, a parasitic infection, are fairly common in African immigrants. Likewise, nodules caused by fungal infections such as coccidioidomycosis are common in the Southwest.

Diagnosis

There are three diagnoses for lung nodules: noncancerous, cancerous, or indeterminate. Indeterminate nodules cannot be definitively defined as benign or malignant.

When healthcare providers see a lung nodule on an X-ray, the first thing they usually do is get any lung imaging tests you may have had in the past to compare them.

If the nodule has been there for a long time and hasn't changed, it's probably not cancer. Further tests may not be needed. However, if you don’t have any prior X-rays for comparison, or if the nodule has changed or is new, further tests may be needed.

If a nodule does not appear to have changed or your healthcare providers believe that there's a low risk of it being cancer, they may take a "wait and watch" approach. They will have you get another imaging test, usually in six months to a year. Single, solitary nodules that have remained unchanged for two or more years do not generally need any further workup.

Imaging Tests

If your nodule is found on a chest X-ray, you may have a computed tomography (CT) scan of your chest. CT scans can provide detailed images and are taken at different angles.

Other tests healthcare providers may order include:

• PET (positron emissions tomography) scan: A PET scan is a functional test that assesses things like the metabolic activity of the nodule. These tests are especially helpful for people who have had previous chest radiation, lung infections, or surgery, which may result in scar tissue. 
• MRI (magnetic resonance imaging): This imaging test uses magnetic fields and radio frequencies and it is rarely used for evaluating lung nodules.

The number of lung nodules that are read by radiologists as indeterminate has increased with the use of lung cancer screening. Hearing that your nodule or nodules are indeterminate can be confusing.

Biopsy

If your nodule has changed in size or appearance, if your diagnosis is uncertain, or if there's a chance that your nodules might be metastatic cancer from another tumor, a sample of your nodule may be required to determine whether it is malignant.

There are different biopsy methods:

• Needle biopsy: You'll be given a local anesthetic. Your healthcare provider will use CT scan images or live imaging to guide a small needle through your chest to get a tissue sample of your lung nodule.
• Bronchoscopy: You'll receive light or conscious sedation. Your healthcare provider will run a long, thin fiberoptic tube with a surgical cutting tool on the end of it down your throat and into your lung to get a sample of your nodule for lab analysis.
• VATS biopsy: You're given a general anesthetic. Healthcare providers use a special kind of video to assist in inserting a tube through the chest wall to get a sample of your lung nodule tissue for analysis. They can also remove the entire lung nodule with this method.

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 found to be metastases when biopsied. Up to 25% were primary lung cancer. 

Lung Nodules and Cancer

There's a less than 1% chance that a nodule smaller than 5 mm will be cancerous. However, a person's actual risk depends on a variety of factors. In people younger than 35, malignancies are very uncommon, while half of all lung nodules in people over age 50 are cancerous.

Here are other factors that can play a role in whether lung nodules that show up on an X-ray are noncancerous or cancerous.

Lung Cancer Screening

Lung cancer screening has been found to decrease the mortality rate from lung cancer by 20%. 

U.S. health officials recommend screening every year for lung cancer if you are between the ages of 50 and 80, still smoke, have quit within the last 15 years, or have a 20-pack-year smoking history.

Pack-year smoking history is a way to gauge how much you've smoked in your lifetime. It means that if you smoked one pack a day for 20 years or two packs a day for 10 years, you should get tested every year for lung cancer.

The recommendations call for using low-radiation-dose CT scans. Screening with chest X-rays has not been shown to reduce the risk of dying from lung cancer.

As with any screening test, there is a risk of false positives, and it's common to find nodules on CT screening. Finding nodules does not always mean cancer. In fact, most small nodules turn out to be benign.

Treatment

The treatment of lung nodules varies widely depending on the diagnosis. Most lung nodules diagnosed using a CT scan are benign. A healthcare provider can determine if the lung nodule is cancerous by watching its growth over time and performing a biopsy (retrieving a sample). If the lung nodule is noncancerous, it might be able to be left alone.

If your nodule is cancerous, detection at this small size is very curable with medication, surgery, or both. In fact, treatment and survival rates for lung cancer, in general, have improved significantly over time. Between 2018 and 2023 alone, lung cancer survival rates in the United States increased by 22%.

Medication

If your lung nodule is cancerous, your healthcare provider may choose to treat you with chemotherapy. Chemotherapy drugs target fast-growing cancer cells. Depending on your type of lung cancer and its stage, you may also receive drugs such as:

• Immunotherapy
• Anti-angiogenesis drugs
  

Video-Assisted Thoracic Surgery (VATS)

This is a minimally invasive surgery that can remove cancerous nodules or non-cancerous nodules that are causing symptoms.

During this procedure, a small tube with a camera at the end is inserted into a small incision between the ribs. The surgeon can remove the nodule with instruments inserted through one or two other small incisions.

Because it is minimally invasive, people who undergo VATS usually recover faster and have less pain than people who undergo more invasive procedures. Hospitalization time is also generally shorter and complications are less likely.

Thoracotomy

A thoracotomy is an open-chest surgery that involves spreading the ribs apart in order to access the lungs. Thoracotomy is much more invasive than VATS and has a longer recovery time. However, it has advantages such as giving the surgeon better visibility of the lungs and any lesions that might have been missed on an imaging scan.

Your healthcare provider may recommend a thoracotomy if your lung tumors are large or advanced or if nearby lymph nodes need to be removed.

Summary

Lung nodules are small lesions in the lungs. They are usually found with an imaging scan such as an X-ray or CT scan.

Lung nodules can have many different causes, including infections, scarring, and malignancies. Because of the possibility that a lung nodule might be cancerous, your healthcare provider will want to do further testing to rule this out.

Benign lung nodules don't need to be treated unless they are causing symptoms. If a lung nodule is cancerous, it may be treated with medication, surgery, or a combination of both.