A 55-year-old with a 2 cm right thyroid nodule on ultrasound undergoes a Tc-99m pertechnetate thyroid scan. The nodule appears as a 'cold' area (no tracer uptake). What percentage of cold thyroid nodules on scintigraphy are malignant, and what is the next recommended investigation?
- A ~50% are malignant; next step is surgical excision without FNAC
- B ~15–20% are malignant; next step is ultrasound-guided FNAC of the nodule ✓
- C ~5% are malignant; observation alone with repeat ultrasound
- D ~80% are malignant; PET-CT is required before FNAC
Correct answer: B. ~15–20% are malignant; next step is ultrasound-guided FNAC of the nodule
Explanation
Approximately 15–20% of cold nodules on thyroid scintigraphy are malignant (most thyroid cancers are non-functioning and appear cold). However, the majority of cold nodules are benign (cysts, adenomas, goitre). Therefore, a cold nodule mandates ultrasound-guided fine-needle aspiration cytology (FNAC/FNA) for tissue diagnosis rather than immediate surgery. Autonomous 'hot' nodules suppress the rest of the gland and are rarely malignant.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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