What causes pulmonary nodules?

From the Guidelines

Pulmonary nodules are caused by a variety of conditions, ranging from benign to malignant processes, with the most common causes including infections, inflammation, benign tumors, and malignancies, as noted in the 2023 study by the American College of Radiology 1. The causes of pulmonary nodules can be broadly classified into several categories, including:

• Infections, such as tuberculosis, fungal infections like histoplasmosis, or bacterial abscesses
• Inflammation, such as rheumatoid arthritis, sarcoidosis
• Benign tumors, such as hamartomas
• Malignancies, such as primary lung cancer or metastases from other cancers
• Vascular abnormalities, congenital conditions, and exposure to environmental or occupational substances like silica or coal dust The risk of malignancy increases with nodule size, particularly those larger than 8mm, irregular borders, upper lobe location, and in patients with risk factors such as smoking history, advanced age, or prior cancer history, as discussed in the 2016 study by the Chest journal 1. The management of pulmonary nodules should be based on the individual's risk factors and the nodule's characteristics, with a focus on minimizing the risk of malignancy and optimizing quality of life, as recommended by the 2023 study by the American College of Radiology 1. Some key points to consider in the management of pulmonary nodules include:
• Most small nodules (less than 6mm) discovered incidentally are benign, but follow-up imaging is often recommended to monitor for changes in size or characteristics
• The frequency and duration of surveillance should be guided by expert consensus-based recommendations, such as those from the Fleischner Society, as noted in the 2013 study by the American College of Chest Physicians 1
• Subsolid nodules, particularly pure ground-glass opacities, often have an indolent course and may require extended-duration surveillance for growth or development of a solid component, as discussed in the 2016 study by the Chest journal 1
• The use of CT scan surveillance, nonsurgical biopsy, or surgical diagnosis should be tailored to the individual's risk factors and preferences, with a focus on minimizing the risk of malignancy and optimizing quality of life, as recommended by the 2023 study by the American College of Radiology 1.

From the Research

Causes of Pulmonary Nodules

• Pulmonary nodules can be caused by various factors, including benign and malignant processes 2, 3, 4, 5
• The majority of pulmonary nodules are benign, with at least 95% of all pulmonary nodules identified being benign, most often granulomas or intrapulmonary lymph nodes 2
• Smaller nodules are more likely to be benign, with the probability of malignancy being less than 1% for all nodules smaller than 6 mm and 1% to 2% for nodules 6 mm to 8 mm 2
• Risk factors such as smoking, age, and exposure to carcinogens can influence the decision-making process for pulmonary nodule management 5

Types of Pulmonary Nodules

• Pulmonary nodules can be categorized as small solid (<8 mm), larger solid (≥8 mm), and subsolid 2
• Subsolid nodules are divided into ground-glass nodules (no solid component) and part-solid (both ground-glass and solid components) 2
• Ground-glass pulmonary nodules have a probability of malignancy of 10% to 50% when they persist beyond 3 months and are larger than 10 mm in diameter 2

Diagnosis and Management

• A definitive diagnosis of pulmonary nodules requires tissue biopsy 4
• The choice of a particular biopsy technique depends on the risks/benefits of the procedure, the diagnostic yield, and local expertise 4
• Management options for pulmonary nodules include surveillance imaging, positron emission tomography-CT imaging, nonsurgical biopsy with bronchoscopy or transthoracic needle biopsy, and surgical resection 2, 3, 4, 5
• Current bronchoscopy and transthoracic needle biopsy methods yield a sensitivity of 70% to 90% for a diagnosis of lung cancer 2