Single rounded opacity less than or equal to 3 cm surrounded by aerated lung; managed by size, density, and risk via Fleischner criteria.
Also known as: SPN, pulmonary nodule, lung nodule, incidental nodule, Fleischner Society
Overview
A solitary pulmonary nodule is a discrete, well- or poorly defined rounded opacity less than or equal to 3 cm in diameter, completely surrounded by aerated lung parenchyma, without associated atelectasis, hilar enlargement, or pleural effusion. Lesions larger than 3 cm are termed masses and are presumed malignant until proven otherwise.
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Risk factors
- Age greater than 40 years; risk rises steeply after 50
- Cigarette smoking — current and former; pack-year burden
- Family history of lung cancer in a first-degree relative
- Occupational exposures: asbestos, radon, silica, arsenic, diesel exhaust
- Personal history of extrathoracic malignancy (especially head/neck, breast, colon, sarcoma, melanoma)
- COPD and pulmonary fibrosis
Pathophysiology
Benign etiologies include infectious granulomas (tuberculosis, histoplasmosis, coccidioidomycosis), hamartomas, intrapulmonary lymph nodes, organizing pneumonia, and rheumatoid nodules. Malignant etiologies are most often primary lung adenocarcinoma, less commonly squamous cell, carcinoid, or solitary metastasis. Subsolid (ground-glass or part-solid) nodules carry the highest probability of representing adenocarcinoma spectrum lesions (atypical adenomatous hyperplasia, adenocarcinoma in situ, minimally invasive adenocarcinoma).
Clinical presentation
Symptoms
- Most nodules are incidental and asymptomatic
- Cough, hemoptysis, weight loss, or chest pain raise concern for malignancy or active infection
- Constitutional symptoms (fever, night sweats) suggest infection or lymphoproliferative disease
Signs / physical exam
- Physical exam is usually normal
- Look for clubbing, supraclavicular lymphadenopathy, hepatomegaly, skin lesions suggesting metastatic disease
Differential diagnosis
- Infectious granuloma — Endemic exposure (Ohio/Mississippi River valleys for histoplasmosis; southwest US for coccidioidomycosis); dense or popcorn calcification; stable for ≥2 years
- Hamartoma — Smooth margins, fat density and popcorn calcification on CT pathognomonic, typically less than 2.5 cm
- Primary lung adenocarcinoma — Spiculated margins, subsolid or part-solid density, growth on serial imaging, smoking history
- Carcinoid tumor — Younger non-smokers, central or peripheral; well-defined, may be hypervascular; somatostatin receptor expression
- Pulmonary metastasis — Known primary malignancy, multiple smooth nodules favored over solitary; history-driven
- Rheumatoid or vasculitic nodule — Known autoimmune disease, may cavitate, often multiple; positive RF/anti-CCP or ANCA
- Intrapulmonary lymph node — Small (<1 cm), oval, subpleural, below the carina; benign on serial imaging
- Arteriovenous malformation — Feeding artery and draining vein on contrast CT; may be hereditary (HHT)
Diagnostic workup
Diagnostic criteria
Fleischner Society 2017 guidelines for incidental pulmonary nodules in adults ≥35 years (do NOT apply to lung cancer screening LDCT, oncology surveillance, or immunocompromised patients). Risk-stratify by patient risk and nodule size, density, and number.
Labs
- CBC, CMP, LDH if malignancy suspected
- Targeted infectious workup based on exposure: histoplasma urine antigen, coccidioides serology, QuantiFERON or PPD, sputum AFB if cavitary
- Tumor markers are not used for diagnosis of SPN
Imaging
- Compare with any prior chest imaging — stability for at least 2 years on solid nodules is strong evidence of benignity
- Dedicated thin-section non-contrast chest CT to characterize size, density (solid, part-solid, ground-glass), margins, location, and calcification pattern
- PET/CT for solid nodules ≥8 mm with intermediate pretest probability of malignancy
- Biopsy options: CT-guided transthoracic needle biopsy (peripheral lesions), navigational or EBUS bronchoscopy (central or hilar lesions), surgical wedge for diagnostic and therapeutic resection
Treatment
First-line
- Apply Fleischner 2017 algorithm by nodule type (solid vs subsolid), size, number, and risk (see table)
- For low-risk solid nodules <6 mm: no routine follow-up
- For high-risk solid nodules <6 mm: optional CT at 12 months
- For solid nodules 6-8 mm: CT at 6-12 months, then 18-24 months
- For solid nodules >8 mm: CT at 3 months, PET/CT, tissue sampling, or referral to multidisciplinary team
- For ground-glass nodules ≥6 mm: CT at 6-12 months then every 2 years for 5 years total
- For part-solid nodules ≥6 mm: CT at 3-6 months; if persistent with solid component ≥6 mm proceed to PET/biopsy/resection
High probability of malignancy (>65%)
- Tissue diagnosis with biopsy or proceed directly to surgical resection if surgical candidate and lesion is accessible
- Staging with PET/CT and brain MRI if non-small cell lung cancer suspected
Intermediate probability (5-65%)
- PET/CT to refine probability; FDG-avid lesions warrant biopsy or resection
- Consider serial CT if comorbidities preclude intervention
Low probability (<5%)
- Serial CT surveillance per Fleischner
- Patient counseling and shared decision making about radiation and anxiety
Complications
- Missed early lung cancer due to inadequate follow-up
- Procedural complications from biopsy: pneumothorax (~15-25% for transthoracic needle biopsy), hemoptysis, infection
- Radiation exposure from repeated CT surveillance
- Patient anxiety and overdiagnosis of indolent ground-glass adenocarcinoma spectrum lesions
PANCE pearls
- Fleischner criteria are for INCIDENTAL nodules — lung cancer screening LDCT findings follow Lung-RADS instead.
- Benign calcification patterns: central, diffuse, laminated/concentric, and popcorn (hamartoma). Eccentric or stippled calcification does not exclude malignancy.
- Doubling time of 20-400 days suggests malignancy; <20 days suggests infection or inflammation; >400 days suggests benignity.
- Subsolid nodules require longer follow-up (up to 5 years) because adenocarcinoma in situ grows slowly.
- Always compare with priors — stable ≥2 years on solid nodules essentially excludes malignancy.
References
- Fleischner Society 2017 — MacMahon H et al. Guidelines for Management of Incidental Pulmonary Nodules Detected on CT Images: From the Fleischner Society 2017. Radiology 2017;284:228-243
- CHEST 2013 — Gould MK et al. Evaluation of Individuals with Pulmonary Nodules: When Is It Lung Cancer? ACCP Evidence-Based Clinical Practice Guidelines. CHEST 2013;143(5 Suppl):e93S-e120S
- ACR Appropriateness — ACR Appropriateness Criteria: Incidentally Detected Indeterminate Pulmonary Nodule (latest revision)
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