From the Guidelines
Lung nodules are most commonly caused by infections, inflammation, benign tumors, and cancer, with smoking being a significant risk factor, particularly for malignant nodules. The causes of lung nodules can be diverse, including:
- Infections such as tuberculosis, fungal infections, or bacterial pneumonia
- Inflammation like rheumatoid arthritis or sarcoidosis
- Benign tumors
- Cancer, with smoking significantly increasing the risk of developing malignant lung nodules
- Exposure to environmental toxins like asbestos, radon, or industrial chemicals
- Scarring due to previous lung infections or injuries
- Certain genetic conditions
According to the most recent and highest quality study 1, the likelihood of malignancy in lung nodules is influenced by factors such as age, smoking history, size of the nodule, presence of spiculated edges, and uptake on PET scans. The study also notes that subsolid nodules, especially pure ground-glass opacities, often have an indolent course and are less associated with smoking history.
The size, appearance, growth rate, and a person's risk factors help determine whether a nodule is likely benign or requires further investigation through additional imaging, biopsy, or surgical removal 1. Proper evaluation is essential as some lung nodules may represent early lung cancer, and the National Lung Screening Trial demonstrated a 20% relative reduction in mortality from lung cancer in patients undergoing annual screening with low-dose chest CT scan compared with chest radiography 1.
In clinical practice, the management of patients with pulmonary nodules is best performed within the context of a multidisciplinary team, comprising radiologists, nuclear medicine specialists, surgeons, pulmonologists, and cancer specialists 1. The Fleischner Society guidelines provide a framework for selecting the interval of follow-up CT scans on indeterminate pulmonary nodules, although the management of pure ground glass nodules remains a topic of debate 1.
From the Research
Causes of Lung Nodules
Lung nodules can be caused by a variety of factors, including:
- Benign conditions such as granulomas or intrapulmonary lymph nodes 2
- Malignant neoplasms, most commonly primary lung cancer followed by metastases of extrapulmonary primary carcinomas 3
- Infections, inflammations, and vascular and congenital abnormalities 4
- Mycobacterial infections, which can resemble lung cancer on chest imaging 5
- Metastases from other cancers, such as breast cancer 6
Risk Factors for Malignant Lung Nodules
Certain risk factors can increase the likelihood of a lung nodule being malignant, including:
- Smoking status and history 3, 5
- Exposure to natural ionic radiation, respirable dust, Diesel engine emissions, asbestos, and polycyclic aromatic hydrocarbons 3
- Larger nodule size, irregular margins, and inhomogeneous density 4
- Presence of tree-in-bud opacities, lymphadenopathy, or emphysema on computed tomography 5
- Higher maximum standardized uptake values from positron emission tomography 5
- Breast cancer cell grade and clinical stage 6
Characteristics of Benign and Malignant Lung Nodules
Benign lung nodules are often characterized by:
- Small size (<6 mm) 2
- Smooth, well-defined margins 4
- Homogeneous density or presence of diffuse, laminated, central or popcorn-like calcifications 4 Malignant lung nodules are often characterized by:
- Larger size (≥8 mm) 2
- Irregular, spiculated margins 4
- Inhomogeneous density or presence of diffuse, irregular amorphous calcifications 4