A lung nodule is a common finding on imaging scans and is often discovered incidentally during other unrelated medical tests. According to studies, about 200,000 new cases are detected each year in the United States alone.

A lung nodule refers to an abnormal growth in the lung measuring less than 3 cm in diameter. If larger than that, it is considered a lung mass.

When a lung nodule is found, some people may feel uneasy or even suspect lung cancer. However, lung nodules can develop for many different reasons. Only a very small number of them are cancerous, while the vast majority are non-cancerous.

Types

Based on their appearance on imaging, lung nodules can be classified into three types :

• Solid nodule, which is solid on imaging.
• Ground glass nodule, like a small, hazy ground glass on imaging.
• Part-solid nodule, which appears on imaging as partially solid and partially ground glass.

Its type, along with other features such as size and shape, helps to estimate the possible cause of the lung nodule and whether it is cancerous.

Symptoms

Lung nodules usually do not have any signs or symptoms. If they are present, the symptoms are often related to conditions other than nodules.

Only in rare cases do lung nodules cause symptoms, but if they do, they should be cause for alarm and further exams.

Causes

Lung nodules can can have many causes. The vast majority of them have little or no impact on health and require only follow-up scans or easy treatment. However, a very small number are serious or even life-threatening.

Common causes of lung nodules are

• Benign cysts or tumours: They can cause lung space-occupying lesions.
• Inflammatory granulomas: Bacterial infections, such as tuberculosis and fungal infections, can trigger fibrosis of the lung tissue, causing nodules and cavities.
• Non-inflammatory granulomas: Sarcoidosis, rheumatoid, rheumatism, etc. can cause accumulation of Aschauff’s microsomes in the lungs, which appear as nodules on CT scans.
• Congenital factors: Abnormal arterial and venous development, abnormal masses containing gas, liquid or semi-solid material, etc.
• Fibrosis: Interstitial pneumonia or pulmonary fibrosis which may appear as a nodule.
• Cancer: Lung cancer, lymphoma or metastatic cancer that has spread to the lungs from other parts of the body, etc.

Risk factors

About 5% of all lung nodules are turned out to be cancerous. The risk of a lung nodule being cancerous depends heavily on some factors.

• Age: The risk of developing lung cancer increases with age. Lung cancer is uncommon or even rare in younger people.
• Smoking history: Long-term smokers have a significantly higher risk of developing lung cancer than non-smokers.
• Personal and family history of cancer: If one has or had cancer, or if one of his/her close relatives has a history of lung cancer, the risk of developing cancer is higher than normal.
• Nodule characteristics: The nature, size and marginal characteristics of nodules are associated with the risk of developing cancer. Stable, non-growing nodules are less likely to become cancerous.
• Occupational exposures: The likelihood of a nodule being cancerous increases with some occupational exposures such as asbestos, uranium and radium.

Diagnosis

Lung nodules can be diagnosed by imaging, pathological cytology, bronchoscopy and biopsy. Of these, a CT scan of the chest is usually the main clinical test.

When imaging reveals a lung nodule, doctors usually make a diagnosis on the basis of its size, characteristics and other risk factors. Depending on the diagnosis, sometimes immediate action is necessary, sometimes follow-up.

Common diagnostic methods include :

• Follow up: If the risk of cancer is low, a regular CT scan is often recommended to monitor any changes of the nodule. Depending on its risk, the follow-up interval may vary from 3 months to 1 or 2 years.
• Lung biopsy: Biopsy is potentially risky as an invasive test. It will be recommended if the nodule is at moderate risk. Commonly performed biopsies include needle biopsy, bronchoscopy and surgical biopsy.
• Surgery: Surgery is an important tool for the definitive diagnosis of lung nodules. It is recommended for nodules with a high risk. Surgical options include televised thoracoscopic surgery, open chest and mediastinoscopy. Thoracoscopic wedge resection is the method of choice for the diagnosis of high-risk nodules.

Treatment

Lung nodules have different causes and therefore different treatments. The vast majority of lung nodules are benign and the treatments are as follows.

• Small inflammatory nodules can heal with anti-infective treatment.
• Tuberculosis may be treated with antituberculosis therapy.
• Fungal infections, such as cryptococcus and aspergillus, require antifungal treatment.
• Benign tumours, such as pulmonary hamartomas and fibromas, usually require regular follow-up and, if necessary, surgery.

In the case of cancer, treatment depends on its type and stage, and the patient’s general health. Cancerous lung nodules are usually early and surgical removal is effective, as well as treatment with the help of radiotherapy, chemotherapy and targeted drugs.

• Surgical resection is the treatment of choice for cancerous lung nodules, including wedge resection, segmental lung resection or lobectomy. Thoracoscopic surgery and open heart surgery are both ways of surgical resection, with the former being the preferred option for less trauma and faster recovery.
• Chemotherapy is more certain for small cell lung cancer, whether early or late. It is also effective for non-small cell lung cancer, but only for palliative purposes.
• Radiotherapy is effective for small cell carcinoma, followed by squamous cell carcinoma and least effective for adenocarcinoma.
• Immunotherapy, which uses the body’s own immune system to fight lung cancer, may result in longer survival for patients.
• Targeted therapy, which identifies and attacks cancer cells with specific genetic characteristics, thereby inhibit tumour growth or even cause the tumour to recede.

Final notes

Lung nodules are very common. The vast majority of them are benign. They can be followed up or treated depending on the diagnosis.

If a lung nodule turns out to be cancer, it is most often in the early stages and requires prompt treatment. Surgery, especially minimally invasive surgery, is usually performed and has a good prognosis.

If you would like to know more about lung nodules, please feel free to talk to a pulmonologist or thoracic surgeon and seek their advice.