Management of a 3×3 cm Thyroid Nodule with Fine-Needle Aspiration (FNA)
Fine-needle aspiration (FNA) should be performed for any thyroid nodule >1 cm, and therefore is strongly indicated for a 3×3 cm thyroid nodule regardless of other features. 1
Rationale for FNA in a 3×3 cm Thyroid Nodule
- A 3×3 cm thyroid nodule carries increased risk of malignancy (approximately 3 times greater than smaller nodules) and requires evaluation with FNA regardless of other sonographic features 2
- While thyroid nodules are common (4-50% of the population depending on diagnostic methods and patient age), thyroid cancer is found in approximately 5% of all thyroid nodules 1
- Larger nodules (>2 cm) warrant evaluation even without suspicious features due to the increased risk of malignancy, as recommended by multiple guidelines 2
Ultrasound Guidance for FNA
- Ultrasound-guided FNA is the preferred approach for a 3×3 cm thyroid nodule due to its superior accuracy compared to freehand technique 2, 3
- Ultrasound guidance by an experienced head and neck radiologist produces the lowest non-diagnostic rate (38%) compared to guidance by a generalist radiologist (65%) or non-US guided FNA (90%) 4
- Ultrasound guidance allows for:
Procedure Considerations
- For a 3×3 cm nodule, multiple passes (typically 2-4) should be performed to ensure adequate sampling 5
- A pathologist's presence during the procedure, when possible, can help assess sample adequacy and reduce non-diagnostic results 3
- If the initial FNA yields non-diagnostic results (Thy1), the procedure should be repeated, as the risk of malignancy in non-diagnostic samples is approximately 4.5% 4
Interpretation of Results
- FNA results will be categorized according to the Bethesda System for Reporting Thyroid Cytopathology 2
- If FNA reveals follicular neoplasia with normal TSH and "cold" appearance on thyroid scan, surgery should be considered 1
- The overall sensitivity of FNA for detecting thyroid neoplasia is approximately 55%, with specificity of 73.7% 3
- Be aware that follicular lesions may be difficult to definitively diagnose by FNA alone and may require histological examination 2
Special Considerations
- For multinodular goiters, the 3×3 cm nodule should be prioritized for FNA 2
- Consider measurement of serum calcitonin as part of the diagnostic evaluation to rule out medullary thyroid cancer (5-7% of all thyroid cancers), which has higher sensitivity compared to FNA 1
- Molecular testing for BRAF, RAS, RET/PTC, and PAX8/PPARγ mutations may be considered as an adjunct to FNA, as the presence of any mutation is a strong indicator of cancer (97% of mutation-positive nodules are malignant) 1
FNA is the most reliable and cost-effective method for evaluating thyroid nodules, with diagnostic accuracy approaching 95% when performed correctly 6.