What is the appropriate workup for a solitary pulmonary nodule (SPN)?

Workup of a Solitary Pulmonary Nodule

The evaluation of a solitary pulmonary nodule (SPN) should follow a structured approach based on risk assessment, nodule characteristics, and sequential imaging, with the Brock risk prediction tool recommended for initial risk stratification of malignancy potential.

Initial Risk Assessment

The first step in SPN evaluation is determining the risk of malignancy based on:

Patient Factors

• Age (older age increases risk)
• Smoking history (current or former smoker)
• Previous history of cancer (especially >5 years ago)
• Family history of lung cancer
• Exposure history (occupational, environmental)

Nodule Characteristics

• Size (larger nodules have higher risk)
• Location (upper lobe location increases risk)
• Morphology:
  • Spiculation (strongly suggests malignancy) 1
  • Border characteristics (irregular borders increase risk)
  • Presence of calcification (benign pattern decreases risk)
  • Cavity wall thickness (thicker walls increase risk)

Risk Stratification Algorithm

For Solid Nodules:

<5mm diameter:

• No routine follow-up in low-risk patients
• Consider 12-month follow-up CT in high-risk patients 1

5-6mm diameter:

• Low-risk patients: No routine follow-up
• High-risk patients: CT at 12 months 1

6-8mm diameter:

• Low-risk patients: CT at 6-12 months, consider follow-up at 18-24 months
• High-risk patients: CT at 6-12 months, then at 18-24 months 1

>8mm diameter:

• Consider one or more of the following based on risk assessment 1:
  • 3-month follow-up CT
  • PET/CT imaging
  • Tissue sampling (biopsy)
  • Surgical evaluation

For Sub-solid Nodules:

Pure Ground Glass Nodules:

• <5mm: No routine follow-up
• ≥5mm: CT at 3 months to confirm persistence, then annual follow-up for at least 5 years if stable 1

Part-Solid Nodules:

• CT at 3 months to confirm persistence
• If persistent, consider biopsy, resection, or close surveillance depending on solid component size 1

Risk Prediction Models

The British Thoracic Society (BTS) guidelines recommend using the Brock model (also known as PanCan model) for initial risk assessment of SPNs 1. This model incorporates:

• Age
• Sex
• Family history of lung cancer
• Emphysema
• Nodule size
• Nodule type (solid, part-solid, ground glass)
• Location
• Count of nodules
• Spiculation

For nodules with a Brock score:

• <10%: Consider CT surveillance
• ≥10%: Consider PET-CT or further investigation 1

Further Diagnostic Evaluation

For Intermediate-Risk Nodules:

• PET/CT scan (particularly useful for solid nodules >8mm) 1
• CT with volumetric analysis to assess growth (volume doubling time) 1
  • VDT <400 days: Suggests malignancy
  • VDT >600 days: Suggests benign etiology

For High-Risk Nodules:

• Tissue diagnosis through:
  • Bronchoscopy (for central lesions) 1
  • CT-guided transthoracic needle biopsy 1
  • Video-assisted thoracoscopic surgery (VATS) biopsy 1

Common Pitfalls to Avoid

1. Ignoring previous imaging: Always compare with prior studies to assess stability or growth 1

2. Overreliance on size alone: Consider all risk factors and morphologic features

3. Inappropriate follow-up intervals: Too short intervals may not allow sufficient time to detect meaningful growth; too long intervals may delay diagnosis of aggressive malignancies

4. Failure to use volumetric measurements: When available, volumetric assessment is more sensitive than diameter measurements for detecting growth 1

5. Neglecting patient factors: Risk assessment should incorporate patient age, smoking history, and comorbidities that may affect management decisions

6. Misinterpreting benign patterns: Certain patterns like diffuse, central, popcorn-like calcifications or fat within nodules strongly suggest benign etiology

By following this structured approach to SPN evaluation, clinicians can appropriately balance the risks of missing early malignancy against unnecessary invasive procedures, ultimately improving patient outcomes through early detection of lung cancer while minimizing harm from excessive testing.