What is the recommended follow-up for a patient with a 9mm pleural base nodule in the lateral peripheral lower right thorax and two 3mm nodules in the right upper lobe (RUL), who had a PET (Positron Emission Tomography) scan 3 months ago showing no typical increase in FDG (Fluorodeoxyglucose) uptake?

Follow-Up CT Surveillance at 3 Months is Recommended

For a 9mm pleural-based nodule with negative PET scan, follow-up CT at 3 months is the appropriate next step, as this nodule size falls into the 5-9mm category requiring serial imaging surveillance rather than immediate biopsy. 1

Risk Stratification and Management Algorithm

The 9mm Pleural-Based Nodule

• This nodule requires CT surveillance at 3 months from the initial scan, followed by repeat imaging at 6 months if no growth is demonstrated. 1
• The European Respiratory Journal guidelines specify that nodules 5-9mm in diameter should undergo HRCT limited to the nodules of record at 3 months after the initial test, and if there is no growth but nodules remain, repeat HRCT at 6 months after the initial test. 1
• The negative PET scan (no typical increase in FDG uptake) is reassuring but does not eliminate the need for surveillance, as PET has limited sensitivity for nodules <1cm and can produce false-negatives in well-differentiated adenocarcinomas and carcinoid tumors. 1
• If growth is manifest at either 3 or 6 months, fine-needle aspiration should be immediately performed. 1

The Two 3mm RUL Nodules

• These 3mm nodules do not require follow-up imaging. 2
• Nodules <5mm have a malignancy risk considerably less than 1%, even in high-risk patients, and the Fleischner Society 2017 guidelines recommend no routine follow-up for solid nodules smaller than 6mm in low-risk individuals. 2
• The British Thoracic Society similarly recommends against follow-up for nodules <5mm in maximum diameter or <80mm³ in volume. 2

Critical Timing Considerations

• You are now at the 3-month mark from the initial scan, which is precisely when the first surveillance CT should be performed for the 9mm nodule. 1
• The surveillance protocol should use thin-section CT (≤1.5mm slices) limited to the nodule of record to minimize radiation exposure while maintaining diagnostic accuracy. 1, 2

PET Scan Interpretation Caveats

• While the negative PET scan is favorable, PET has approximately 97% sensitivity but only 78% specificity, and is best used for nodules ≥1cm. 1
• The 9mm nodule falls just below the optimal size threshold for PET reliability, making growth assessment on CT more critical than the PET result alone. 1
• False-negative PET results can occur with carcinoid tumors, well-differentiated adenocarcinomas, and bronchioloalveolar cell carcinomas regardless of size. 1

Growth Assessment Protocol

• A 25% volume increase defines significant growth requiring escalation to biopsy or surgical evaluation. 2
• Volume doubling time (VDT) <400 days indicates growth and requires further workup with PET-CT, biopsy, or resection. 2
• Volumetric analysis is preferred over diameter measurements when available, as it more accurately detects growth. 2

When to Escalate Management

• If the 3-month CT shows growth in the 9mm nodule, proceed immediately to fine-needle aspiration. 1
• If no growth at 3 months but the nodule persists, repeat CT at 6 months from baseline. 1
• If no growth is manifest at 6 months, surveillance can stop. 1
• Percutaneous lung biopsy is rated as "usually appropriate" (8/9) for nodules ≥8mm when results will alter management. 1, 2

Common Pitfalls to Avoid

• Do not skip the 3-month surveillance based solely on the negative PET scan – the nodule size mandates CT follow-up per established guidelines. 1
• Do not perform immediate biopsy without documented growth, as the negative PET and intermediate size favor surveillance first. 1
• Ensure the CT uses thin sections (≤1.5mm) to enable accurate volumetric comparison. 2
• Do not extend surveillance intervals beyond guideline recommendations, as the 5-9mm size category has specific timing requirements. 1