Size-Dependent Strategy for Ultrasound-Guided Fine-Needle Aspiration Biopsy of Thyroid Nodules: A Comparison of In-Plane and Out-of-Plane Techniques

Objective To compare the clinical efficacy of ultrasound-guided in-plane versus out-of-plane fine-needle aspiration biopsy techniques for identifying thyroid nodules of different sizes and to explore individualized aspiration strategies on the basis of nodule size. Methods: A total of 492 patients who underwent ultrasound-guided fine-needle aspiration biopsy of thyroid nodules from January 2024 to February 2025 were retrospectively included and divided into an in-plane group (n = 275) and an out-of-plane group (n = 217) according to nodule size (group A: <0.5 cm; group B: 0.5 ~ 1.0 cm; group C: >1.0 cm), and the two groups were compared in terms of the satisfaction rates of the specimens, operation times and complication differences and further stratified to analyze the effects of complex anatomical locations (adjacent vessels/trachea). Results The advantage of the in-plane method was significant for ≤ 1.0 cm nodules, with overall specimen satisfaction rates of 98.2% and 98.1% in Groups A and B, respectively, which were significantly greater than those of the out-of-plane method (65.5% and 81.2%, respectively), with a significantly lower percentage of Bethesda Class I nodules (Group A: 1.8% vs. 34.5%; Group B: 1.9% vs. 18.8%) and a significantly lower complication rate in Group A than in the out-of-plane method for complex-location (neighboring vessel/trachea) nodules. The complication rate was lower in Group A for the in-plane approach than for the out-of-plane approach, and the differences were statistically significant (P < 0.05). For > 1.0 cm nodules, there was no statistically significant difference in the overall specimen satisfaction rate between the two puncture methods (96.8% and 98.3%, respectively, p = 0.29), but the out-of-plane method had a higher specimen satisfaction rate in complex locations (adjacent vessels/trachea) (97.1% vs. 84.6%, p = 0.038), and the complication rate was lower (15.4% for the in-plane method vs. 0% for the out-of-plane approach, p = 0.02). The mean puncture time was shorter for the in-plane method than for the out-of-plane method for ≤ 1.0 cm nodules (4.10 ± 1.0 min, 5.50 ± 2.3 min, respectively, p < 0.001) but shorter for the out-of-plane method than for the in-plane method for > 1.0 cm nodes with complex locations (adjacent to the blood vessels/trachea) (4.2 ± 1.1 minutes, 5.8 ± 1.5 minutes, p < 0.001). Conclusion The in-plane approach is preferred for ≤ 1.0 cm nodules; the noncomplicated location of > 1.0 cm nodules allows for flexibility, and the out-of-plane approach is recommended to balance efficiency and safety if adjacent to blood vessels/trachea.