What is the diagnostic approach for a smooth margin nodular lesion?

Diagnostic Approach for Smooth Margin Nodular Lesions

Smooth margin nodular lesions are significantly less likely to be malignant compared to those with irregular or spiculated margins, with smooth margins having a likelihood ratio of 0.2 for malignancy in pulmonary nodules. 1

General Characteristics of Smooth Margin Nodules

• Smooth or polygonal margins in nodular lesions are associated with a five times lower likelihood of malignancy (LR 0.2) compared to irregular or spiculated margins 1
• The combination of round shape, smooth margins, and low attenuation in solid nodules has been reported to be 100% predictive of benignity in pulmonary nodules 1, 2
• Nodules with diffuse, central, laminated, or popcorn pattern of calcification or macroscopic fat should not require follow-up or further investigation as they are typically benign 3, 2
• Smooth margin nodules may still require evaluation as margin characteristics alone cannot definitively rule out malignancy 1, 4

Diagnostic Algorithm Based on Location

For Pulmonary Nodules

1. Initial Assessment:

   • Review prior imaging tests to establish stability or growth 1
   • Characterize the nodule with thin-section CT to assess size, shape, margins, and attenuation 1, 3

2. Risk Stratification Based on Size:

   • Nodules <5 mm or <80 mm³: generally do not require follow-up 3
   • Nodules 5-8 mm: consider CT surveillance 3
   • Nodules ≥8 mm or ≥300 mm³: require comprehensive risk assessment 3

3. Risk Assessment for Larger Nodules:

   • Use validated prediction models (e.g., Brock model) that incorporate clinical and radiological risk factors 3
   • Consider clinical factors: age, smoking history, previous malignancy 3, 2
   • Evaluate radiological features: size, location, density, presence of calcification 3, 2

4. Management Based on Risk Assessment:

   • Low risk (<10% probability of malignancy): CT surveillance 3
   • Intermediate risk (10-70%): PET-CT for further assessment 3
   • High risk (>70%): Consider tissue diagnosis or excision 3

5. Special Considerations for Solid Nodules with Smooth Margins:

   • If stable for at least 2 years, no additional diagnostic evaluation is typically needed 1
   • For growing nodules, consider PET-CT or tissue sampling 1, 3

For Skin Nodules

• Reflectance confocal microscopy (RCM) and optical coherence tomography (OCT) can be used as non-invasive techniques to evaluate nodular skin lesions 5
• In dermal nevi (benign), hyporeflective nests at OCT and dense nests at RCM are common findings 5
• Correlation between imaging findings and histopathology is essential for definitive diagnosis 5

For Ovarian/Adnexal Nodules

• For smooth solid-appearing ovarian lesions, external contour assessment is a key component of risk stratification 1
• The O-RADS US risk stratification system can be applied to categorize risk and guide management 1

Specific Features Suggesting Benignity in Smooth Margin Nodules

• Diffuse, central, laminated, or popcorn patterns of calcification 1, 2
• Presence of intranodular fat density (specific for hamartoma) 1, 2
• Stability for at least 2 years 1, 2
• Peripheral location in pulmonary nodules 2
• Typical perifissural or subpleural location (for pulmonary nodules) 3

Pitfalls and Caveats

• Smooth margins alone cannot definitively exclude malignancy, particularly in larger nodules 1, 4
• Some malignant lesions may present with deceptively smooth margins in early stages 6, 7
• In the NELSON lung cancer screening trial, nodule density did not have discriminative power in distinguishing benign from malignant solid pulmonary nodules 4
• Subcentimeter nodules may be difficult to characterize accurately, requiring follow-up imaging to assess stability 3, 8
• False negatives can occur with PET-CT, particularly with small nodules or certain histological subtypes 3

When to Consider Tissue Sampling

• For nodules ≥8 mm with concerning features despite smooth margins 3
• When nodule shows growth during surveillance 1, 3
• When risk assessment indicates intermediate to high probability of malignancy 3
• When results will alter management decisions 3