What is a lung nodule?
A lung nodule, also known as a pulmonary nodule, is a a round or opaque opaque mass in the lung that is seen in a chest X-ray or thoracic CT scan. It is more accurately defined as a discrete nodule that is equal to or less than 3 centimeters in diameter. Larger opacities are known as growths or masses. Most pulmonary nodules are asymptomatic and are found incidentally on x-ray or CT scan when investigating other conditions.
Types of Lung Nodules
A lung nodule may be due to a number of causes and are not always cancerous. Benign tumors or granulomas are other fairly common causes of a lung nodule.
- A malignant tumor, or cancer, is when the genes of the cells becomes damaged and the abnormal cells grow uncontrollably. This rapidly invades and destroys surrounding tissue and can spread via the blood stream or lympathic system to distant sites (metastases).
- With a benign tumor, there is an overgrowth of tissue as the number of cells increases greatly but the cells are not abnormal. These growths may, however, compress surrounding structures and cause various symptoms. Some may also have the potential to become malignant.
- A granuloma is a collection of immune cells and inflammatory tissue which develops when the body attempts to wall off certain pathogens that cannot be destroyed or eliminated from the body. This is seen with certain bacteria, like Mycobacterium tuberculosis which causes TB, or fungi.
Sometimes there may be fat deposition within a benign tumor or calcification of the tumor or granuloma. These may also be evident to varying degrees on an x-ray or CT scan.
Risk Factors for Malignant Nodules
It is helpful to examine previous x-rays to assess if the nodule is growing or invading surrounding tissue in a manner that has cancer characteristics. When assessing a lung nodule, it is important to take certain factors into consideration with regards to whether the nodule may be benign or malignant.
A lung nodule is more likely be malignant if it is found in a :
- Smoker – long term smokers and heavy smoking
- Person with a family history of lung cancer
- Worker exposed to asbestos, silica and radioactive materials
- Older person
Is a nodule on the lung cancerous?
Apart from the risk factors mentioned above that may increase the chances of a nodule being cancerous, other radiological features also have to be taken into consideration. This may prompt the doctor to conduct further investigations like a percutaneous needle biopsy to confirm or exclude a malignancy.
- Most nodules that are greater than 3 cm in diameter are malignant. Nodules less than 1 cm are less likely to be cancerous although there is a risk of malignancy if the person is a smoker.
- A nodule that is not smooth (spiculated ~ irregular margin with lines) is more likely to be malignant.
- Malignant lesions are usually partly solid whereas benign tumors are generally solid.
- Calcified lesions are less likely to be cancerous but is more often seen with benign tumors or granulomas.
- Most lung cancers occur on the upper lobes, especially of the right lung. However, this does not exclude the possibility that a malignancy may occur at other locations.
- Enlarged lymph nodes, especially the hilar and mediastinal nodes, are more frequently seen with cancer.