Ultrasound-guided fine-needle aspiration of thyroid nodules measuring less than 5 mm: effects on specimen adequacy and diagnosis.

We aimed to assess the adequacy and efficacy of ultrasound (US)-guided fine-needle aspiration (US-FNA) for small solid thyroid nodules (SSTNs) with the largest diameter <5 mm and compared these according to nodule size.Among 656 SSTNs in 569 patients, each SSTN was classified into 1 of 4 groups according to the largest diameter: 1 mm ≤ group A < 2 mm; 2 mm ≤ group B < 3 mm; 3 mm ≤ group C < 4 mm, and 4 mm ≤ group D < 5 mm. We compared the adequacy and efficacy of US-FNA between these groups using histopathologic results as a reference standard.571 (87.0%) SSTNs were adequately sampled by US-FNA and 200 of these were histopathologically confirmed. The adequacy of US-FNA for SSTNs varied according to the nodule diameter: the smaller the nodule diameter, the lower the diagnostic adequacy. The diagnostic efficacy of US-FNA for SSTNs showed a significant relationship with nodule size: diagnostic efficacy in groups A and B was lower than in groups C and D.The adequacy of US-FNA for SSTNs tended to decrease with decreased nodule size, and diagnostic efficacy of US-FNA for SSTNs with the largest diameter <3 mm was lower than for those ≥3 mm.