OVERVIEW

What is a pulmonary nodule?

A pulmonary nodule refers to an abnormal tissue in the lung with a diameter of 3 cm or less, which may be round or irregular in shape. If lung tissue is compared to a fluffy cotton ball, a pulmonary nodule can be seen as "a harder lump clumped together within the cotton."

On imaging (such as CT scan results), it appears as a shadow with increased density, resembling a brighter spot. It may be single or multiple, with clear or unclear boundaries^[1]. However, the results usually do not indicate "accompanied by pleural effusion or enlarged hilar and mediastinal lymph nodes."

Pulmonary nodules are often asymptomatic when discovered, and CT scans or chest X-rays typically show no other characteristic abnormalities.

Pulmonary nodules can be benign or malignant. Malignant nodules are often tumor tissues, so when a pulmonary nodule is detected, it is recommended to seek further evaluation by a doctor promptly. Early detection and treatment of malignant tumors are crucial.

Are pulmonary nodules common?

Yes. Although there is still a lack of research on the incidence of pulmonary nodules, data from lung cancer screenings show that the overall detection rate of pulmonary nodules through low-dose CT (LDCT) is 26.32%–31%, with over 20% being multiple pulmonary nodules^[2]. In other words, nearly one-third of participants in these screening studies had pulmonary nodules.

Moreover, with increased health awareness and advancements in medical imaging technology, more people are opting for high-resolution CT scans of the lungs during physical examinations or outpatient visits.

Since CT scans have much higher resolution than chest X-rays, the number of people diagnosed with pulmonary nodules has gradually increased. However, this does not mean the incidence of pulmonary nodules has risen significantly, so excessive panic is unnecessary.

What are the types of pulmonary nodules?

Based on the density of pulmonary nodules (higher density appears brighter on X-rays or CT scans), they can be divided into three categories:

• Solid nodule: Refers to a nodule entirely composed of soft tissue density, with relatively uniform density, where the images of blood vessels and bronchi are obscured^[1].
• Ground-glass nodule (GGN): Refers to a vague nodular shadow in the lung with clear or unclear boundaries. The nodule's density is slightly higher than the surrounding lung tissue, but the outlines of blood vessels and bronchi are still visible^[1].
• Part-solid nodule: Refers to a nodule containing both ground-glass and solid soft tissue densities, with uneven density^[1].

Among these, part-solid nodules have the highest probability of malignancy, followed by ground-glass nodules and solid nodules.

Based on the number of nodules, they can be divided into two types:

• Solitary pulmonary nodule: Typically asymptomatic, appearing as a well-defined soft tissue shadow with increased density, ≤ 3 cm in diameter, and surrounded by aerated lung tissue^[1].
• Multiple pulmonary nodules: Defined as two or more nodules. Multiple pulmonary nodules often present as a single nodule accompanied by one or more small nodules. It is generally believed that diffuse pulmonary nodules numbering more than 10 are mostly caused by metastatic malignant tumors or benign conditions (inflammatory diseases due to infectious or non-infectious factors)^[1].

Which department should you visit after discovering a pulmonary nodule?

If a pulmonary nodule is found during a physical examination, you can usually visit the respiratory medicine department. If the examination report suggests a suspicion of malignancy, you may also consider visiting the oncology or thoracic surgery department in addition to respiratory medicine.

If the pulmonary nodule is discovered during diagnostic tests for other conditions, you can directly consult the doctor in the relevant department.

SYMPTOMS

What are the symptoms of pulmonary nodules?

Pulmonary nodules usually do not have obvious characteristic symptoms and are often accidentally discovered during physical examinations or lung examinations for other diseases or discomfort. The key is to detect lung lesions early through pulmonary nodules and determine their benign or malignant nature as soon as possible.

Under what circumstances are pulmonary nodules more likely to be benign?

During regular follow-up examinations (such as annual routine check-ups or follow-ups as required by a doctor), pulmonary nodules with the following changes are more likely to be benign^[1]:

• Significant changes in external features of the lesion in a short period, with no lobulation or extremely deep lobulation, and edges becoming smoother or blurred (often reflected in examination reports);
• Uniform or fading density;
• Shrinkage or disappearance of the nodule without an increase in density;
• Rapid enlargement of the nodule, with a doubling time < 15 days (the time it takes for the nodule to double in size);
• Stable solid nodule lesions for more than two years (excluding ground-glass nodules).

What manifestations of pulmonary nodules suggest malignancy?

Pulmonary nodules with the following changes during follow-up examinations are more likely to be malignant^[1]:

• Increase in nodule diameter, with a doubling time consistent with tumor growth patterns (the time it takes for the nodule to double in size; most malignant tumors have a doubling time of about 20–400 days^[3]);
• Stable or enlarged nodules with the appearance of solid components (increased density);
• Shrinking nodules but with the appearance or increase of solid components;
• Blood vessel formation consistent with malignant pulmonary nodule patterns (vessels gathering near the nodule or abnormal vascular proliferation within the nodule);
• Presence of lobulation, spiculation, and/or pleural indentation.

CAUSES

What are the common causes of pulmonary nodules?

The vast majority of pulmonary nodules are caused by benign conditions^[3], including:

• Bacterial infections: such as Staphylococcus aureus, Pneumocystis jirovecii, Cryptococcus neoformans, Histoplasma, Coccidioides, tuberculosis, or nontuberculous mycobacterial infections;
• Benign tumors: such as hamartomas, fibromas, leiomyomas, hemangiomas, and alveolar cell adenomas;
• Vascular diseases: such as pulmonary arteriovenous malformations, pulmonary infarction, pulmonary varices, and pulmonary contusions or hematomas;
• Inflammatory diseases: such as granulomatosis with polyangiitis, rheumatoid arthritis, sarcoidosis, amyloidosis, and rounded atelectasis;
• Perifissural lymph nodes and developmental abnormalities: such as bronchogenic cysts.

In addition, malignant causes of pulmonary nodules include primary lung cancer, pulmonary metastases, and carcinoid tumors.

DIAGNOSIS

What tests are needed after discovering a pulmonary nodule?

After discovering a pulmonary nodule, the key focus is evaluating whether it is benign or malignant. Evaluation methods include clinical information, imaging, tumor markers, functional imaging, non-surgical and surgical biopsies, as detailed below:

Clinical Information: Clarify patient details such as age, occupation, smoking history, history of chronic lung diseases, personal and family tumor history, etc., to assist doctors in differential diagnosis.

Imaging Tests:

1. X-ray: Not recommended, as most nodules <1 cm are not visible on chest X-rays.
2. Chest CT: Helps determine the nodule's location, size, shape, density, margins, and internal features. Commonly recommended for pulmonary nodule evaluation.

Tumor Markers: Currently, there are no specific biological markers (tumor markers) for the clinical diagnosis of pulmonary nodules^[3]. Common lung tumor markers, such as carcinoembryonic antigen (CEA), are generally not used for screening but rather for evaluating treatment efficacy.

Functional Imaging: For nodules with solid components >8 mm, PET-CT can help differentiate benign from malignant nodules. Additionally, dynamic contrast-enhanced CT scans have diagnostic value in distinguishing benign and malignant nodules^[4].

Non-Surgical Biopsy:

1. Bronchoscopy: The most common method for diagnosing pulmonary nodules^[4], including direct brushing, biopsy, transbronchial lung biopsy (TBLB) under fluoroscopy, and bronchoalveolar lavage for cytological and histological diagnosis.
2. Transthoracic Needle Biopsy (TTNB): Performed under CT or ultrasound guidance, this involves inserting a needle through the chest wall into the lesion to obtain lung tissue. It has high sensitivity and specificity for peripheral nodules but carries risks such as limited tissue sampling and potential patient injury^[3].

Surgical Biopsy:

1. Thoracoscopy: Suitable for nodules where pathological specimens cannot be obtained via bronchoscopy or TTNB, especially small nodules or those highly suspected to be malignant. Thoracoscopic resection can provide a definitive diagnosis.
2. Mediastinoscopy: An effective method for confirming nodule nature and assessing lymph node staging, currently the gold standard for evaluating mediastinal lymph node status in pulmonary nodule patients^[4].

TREATMENT

How to Treat Pulmonary Nodules?

Pulmonary nodules are a general term often found in imaging reports like CT scans, rather than a specific disease. They encompass a wide range of conditions. Therefore, without a clear diagnosis, specific treatment is usually not administered^[4].

Instead of treatment, assessing and managing the risk of pulmonary nodules is more critical—primarily determining whether the nodule could be malignant. Common scenarios include:

1. If a larger pulmonary nodule is detected, doctors will evaluate it based on size and morphology. If malignancy is suspected (e.g., nodules larger than 8 mm in diameter), further tests such as biopsy or contrast-enhanced CT may be required.

2. Of course, most nodules are likely benign. Experienced doctors can often determine this directly from imaging results. In such cases, patients are usually advised not to worry or seek treatment but to return for follow-up examinations, typically every six months to a year. Specific recommendations should be discussed with the doctor.

   • If follow-up shows the nodule is growing, the doctor may recommend further diagnostic tests.
   • If the nodule remains unchanged or shows minimal changes, continued observation is usually advised, and no action may be needed if there are no symptoms.

3. Apart from malignancy, some benign conditions, such as tuberculosis or sarcoidosis, may also cause nodules. These often come with other symptoms and require targeted treatment for the underlying disease.

Therefore, specific treatment for pulmonary nodules depends on a doctor's evaluation and diagnosis. For more details, you can search for related conditions on the Dingxiang Doctor App.

DIET & LIFESTYLE

What should patients with pulmonary nodules pay attention to in daily life?

• After discovering pulmonary nodules, it is necessary to quit smoking, alcohol, betel nut, and other unhealthy habits with clear carcinogenic effects as soon as possible;
• Maintain good sleep and dietary habits, and engage in appropriate exercise and physical activity;
• Under the guidance of a specialist, attend regular follow-up visits and re-examinations (e.g., every six months or annually);
• Avoid excessive anxiety or loss of appetite, and do not blindly believe various "suspected cancer" claims on non-professional websites, which may increase psychological stress.

PREVENTION

Can lung nodules be prevented?

There is no clearly effective prevention method^[3].

Lung nodules have various causes. Apart from changing unhealthy habits (such as quitting smoking and alcohol), taking protective measures in toxic or hazardous work environments (e.g., wearing appropriate masks in dusty workplaces), and reducing outdoor activities and using personal protection during severe smog, there is currently no clearly effective prevention method.

Do not blindly believe unscientific claims such as "lung cleansing."

Should ordinary people get tested if they suspect lung nodules?

In most cases, no.

Although lung nodules are common, the probability of malignant nodules is relatively low. Some studies suggest only a 1% chance of lung cancer^[3]. For individuals who maintain a healthy lifestyle (no smoking, no alcohol, regular routine, etc.) and have no family history, the likelihood of malignant lung nodules is even lower.

Additionally, ordinary X-rays may not detect nodules, and at least a CT scan is required. CT scans involve higher radiation exposure and are relatively expensive.

If there are no physical discomforts or suspicious findings during routine check-ups, additional testing for lung nodules is generally unnecessary.