What is the appearance of lung cancer on a computed tomography (CT) scan?

Radiographic Appearance of Lung Cancer on CT Scan

Lung cancer on CT scan typically appears as a solid nodule with spiculated or irregular margins, though it can also present as ground-glass opacities, part-solid nodules, or areas of consolidation depending on the specific cancer type and stage. 1

Characteristic Features of Lung Cancer on CT

Solid Nodules

• Size: Larger nodules have higher probability of malignancy
  • Nodules ≥8 mm have significantly higher risk 2
  • Nodules >20 mm are most likely to be malignant 1
• Margins: Spiculated (irregular, star-like projections) or ragged margins increase likelihood of malignancy by more than five times 1
• Shape: Irregular shape more concerning than round/oval shape
• Location: Upper lobe nodules have higher risk of malignancy than lower lobe lesions 1
• Density: Variable, but solid nodules with spiculation are highly suspicious

Ground-Glass and Part-Solid Nodules

• Part-solid nodules (mixed solid and ground-glass components) have the highest malignancy rate (up to 63%) 3
• Pure ground-glass nodules (GGNs) have approximately 18% malignancy rate 3
• Persistent GGNs >10 mm have 10-50% probability of malignancy when they persist beyond 3 months 2
• Often represent adenocarcinoma with lepidic growth pattern, adenocarcinoma in situ, or minimally invasive adenocarcinoma 1

Advanced Disease Presentations

• Mediastinal invasion: Direct extension into adjacent structures
• Hilar/mediastinal lymphadenopathy: Enlarged lymph nodes (>1 cm in short axis)
• Pleural retraction: Pulling of pleura toward the nodule, increasing likelihood of malignancy by nearly twice 1
• Vascular invasion: Vessel sign (vessels leading to nodule)
• Superior vena cava syndrome: Widened mediastinum or right hilar mass 1
• Multiple pulmonary nodules: May represent intrapulmonary metastases or synchronous primary tumors 1

Specific Lung Cancer Patterns

Multifocal Lung Adenocarcinoma

• Multiple pure ground-glass or part-solid nodules on CT scan
• More common in women and non-smokers
• Generally better prognosis with less lymph node involvement 1

Pneumonic-Type Lung Adenocarcinoma

• Presents with patchy areas of consolidation or ground-glass opacity
• Similar appearance to pneumonia
• Often corresponds to invasive mucinous adenocarcinoma histologically 1

Separate Pulmonary Nodules

• Solid nodules in different lobes may represent either:
  • Separate primary lung cancers
  • Intrapulmonary metastases (typically considered when in same lobe as T3, different ipsilateral lobes as T4, and contralateral lungs as M1a) 1

Pitfalls in CT Interpretation

• Benign calcification patterns (diffuse, central, laminated, popcorn) strongly suggest benignity 1
• Small nodules (<6 mm) have <1% probability of malignancy but should not be ignored as some cancers can present as slow-growing small nodules 1, 4
• Endobronchial and central lesions may be difficult to recognize on low-dose CT due to absence of intravenous contrast 5
• Focal lesions within pre-existing lung disease (fibrosis, apical scars) can be early manifestations of lung cancer but may be difficult to detect 5

Growth Patterns

• Growth rate varies widely from indolent to aggressive
• Some nodules may remain stable for years before showing malignant growth 4
• Solid component growth in part-solid nodules is particularly concerning for malignancy 1
• Even small nodules that remain stable for 12-24 months may later develop into cancer 4

Understanding these characteristic appearances of lung cancer on CT is crucial for early detection and appropriate management, as early-stage lung cancers have significantly better survival rates than advanced disease.