Understanding Lung Nodules: Causes, Types, and What to Expect

A pulmonary nodule is a round/oval opacity ≤3 cm on imaging. >3 cm = mass. Most are benign; evaluation stratifies risk.

Benign Causes

• Granulomas: Healed TB, histoplasmosis, coccidioidomycosis (calcified).
• Hamartoma: "Popcorn" calcification, fat density.
• Intrapulmonary lymph nodes
• Rounded atelectasis, infarction, vasculitis nodules

Malignant Causes

• Primary lung cancer (adenocarcinoma, squamous, small cell)
• Metastases (breast, colon, renal, melanoma, sarcoma)
• Lymphoma

Risk Stratification (Fleischner Society Guidelines)

• Size: <6 mm low risk; 6–8 mm intermediate; >8 mm higher risk.
• Morphology: Solid > part-solid > ground-glass (GGN) for malignancy probability per mm.
• Growth: Volume doubling time 400–600 days typical for cancer; <400 or >600 favors benign.
• Patient factors: Age, smoking, cancer history, family history, emphysema.

Management

• Low risk: CT surveillance (3, 12, 24 months).
• Intermediate: PET-CT, biopsy, or short-interval CT.
• High risk: Biopsy (CT-guided, bronchoscopic, surgical) or resection.

Key Message

Most nodules are benign. Systematic follow-up per guidelines avoids unnecessary procedures while catching cancer early.