Pulmonary nodules are commonly detected during routine lung cancer screening on low-dose chest computed tomography (CT) or incidentally on other imaging. Approximately 1.6 million people in the United States are diagnosed with pulmonary nodules annually, with most being asymptomatic. The etiology of pulmonary nodules ranges from benign to malignant, necessitating a structured approach to evaluation. The US Preventive Services Task Force recommends lung cancer screening for high-risk individuals because it reduces lung cancer mortality. Management of pulmonary nodules relies on statistical models to estimate malignancy risk by incorporating radiographic features and clinical history. The Fleischner Society provides guidelines for managing incidentally detected nodules, whereas the Lung CT Screening Reporting and Data System offers a framework for risk stratification and surveillance. Radiographic characteristics suggestive of malignancy include part-solid or ground-glass appearance, large nodule size, spiculated margins, vascular convergence, and pleural retraction. Risk factors such as smoking history, older age, chronic obstructive pulmonary disease, cancer history, and environmental or occupational exposure to toxins further increase the probability of malignancy. Management strategies are dependent on malignancy risk and may include serial imaging for low-risk nodules and invasive procedures such as biopsy or surgical resection for high-risk lesions. Referral to a specialist is warranted for nodules with a high likelihood of malignancy or if tissue diagnosis is required.
Case 2. JP is 58-year-old current smoker with a 25-pack-year history and stage I chronic obstructive pulmonary disease. He presents to you for follow-up after low-dose chest computed tomography (CT) performed for lung cancer screening showed a 6-mm solid pulmonary nodule in the right lower lobe. The radiologist’s report recommends repeating CT in 6 months. JP tells you he is concerned about the risk of malignancy.
Definition and Prevalence
Pulmonary nodules are focal lung abnormalities that appear denser than surrounding tissue. They are often detected incidentally on imaging performed for unrelated reasons and are identified in approximately 30% of chest CT scans in the United States.1 Each year, approximately 1.6 million people in the United States are diagnosed with pulmonary nodules, and nearly one-half of these people have multiple nodules.2,3 Approximately 95% of nodules are benign.1 The probability of malignancy depends on radiographic characteristics and patient history.
Presentation
Most pulmonary nodules are asymptomatic, appearing as dense opacities less than 3 cm in diameter.4 Small nodules rarely cause symptoms, although the clinical presentation may vary based on size, location, and effects on surrounding structures. In some cases, patients experience respiratory symptoms such as chest pain, cough (productive or nonproductive), or hemoptysis. Larger nodules (more than 20 mm in diameter) and multiple nodules are more often associated with symptoms.5
Etiology and Risk Factors
BENIGN CAUSES
The most common benign nodules are granulomas, often caused by prior infections or inflammatory conditions (eg, sarcoidosis, silicosis). Nonneoplastic nodules may arise from intrapulmonary lymph nodes, interstitial lung disease, or infections (ie, bacterial, fungal, viral, or mycobacterial). Some benign nodules, such as hamartomas, have a neoplastic origin.6
Nodules with calcification or rapid size doubling times (ie, in less than 20 days) are typically infectious or inflammatory.7 Nodules smaller than 6 mm in diameter have less than a 1% risk of malignancy, and perifissural nodules are uniformly benign.1,3 Management of benign nodules depends on nodule size and includes no further action if low-risk and smaller than 6 mm, or surveillance with repeat CT and noninvasive tests such as sputum cultures and serologic studies. If there is uncertainty, invasive diagnostic testing (eg, bronchoscopy with bronchoalveolar lavage and biopsy) may be necessary.
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