In evaluating a solitary pulmonary nodule on CT, what size thresholds guide follow-up or biopsy decisions?

• A. Nodules <6 mm often no immediate workup; 6-8 mm follow-up at 12 months; >8-10 mm may prompt biopsy or PET; consider high-risk features.
• B. Nodules <6 mm require biopsy; 6-8 mm immediate treatment; >10 mm no workup.
• C. All nodules require biopsy.
• D. Nodules >20 mm require no workup.

Answer: (A)

Size on CT is the key factor that guides the next step in evaluating a solitary pulmonary nodule. Nodules under about 6 mm have a very low likelihood of cancer in average-risk individuals, so many guidelines recommend no immediate workup and instead watchful monitoring if there are no high-risk features. For nodules in the 6–8 mm range, the risk is intermediate, so the usual plan is to obtain a follow-up CT in roughly 6 to 12 months to assess for growth; if stable, surveillance continues with longer intervals. When nodules reach about 8–10 mm or larger, the probability of malignancy increases enough that further testing is often pursued, such as PET imaging or tissue biopsy, especially if there are high-risk features like irregular or spiculated margins, rapid growth on serial imaging, or a significant smoking history. This approach aligns with the described strategy of no immediate workup for very small nodules, a 12-month follow-up for mid-sized nodules, and consideration of biopsy or PET for larger nodules, with attention to risk factors to tailor the plan.