Effects of nodule characteristics on sampling number and duration of thyroid fine-needle aspiration biopsy: size does not matter, but cystic degeneration ratio does.

Background Ultrasound-guided fine needle aspiration biopsy (FNAB) of thyroid nodules, though the most accurate method to rule out malignancy, still has an inherent risk of yielding non-diagnostic specimens despite immediate assessment of specimen adequacy by an on-site cytopathologist. Purpose To evaluate the effects of nodule volume and extent of cystic degeneration on total biopsy time and number of aspirations required for obtaining an adequate specimen. Material and Methods A total of 510 patients underwent FNAB by a single radiologist accompanied by a cytopathologist who immediately assessed each sample for specimen adequacy. All sampled nodules were single and had one maximum diameter > 10 mm. Nodule volumes and cystic degeneration ratios were calculated prior to the intervention. Aspirations were repeated until the cytological material was deemed adequate by the cytopathologist; the number of aspirations and total biopsy time were then recorded. Results Nodule volumes did not have significant effect on neither number of aspirations necessary for achieving specimen adequacy ( P > 0.05) nor total biopsy time (r = -0.148 with P = 0.001). Predominantly cystic nodules, compared to predominantly solid nodules, required more sampling per nodule (4.58 ± 1.11 vs. 3.44 ± 1.19 aspirations, P = 0.001) and longer total biopsy time (16.40 ± 6.19 vs. 11.15 ± 6.18 min, P = 0.001). Conclusion Predominantly cystic nodules require allocation of more time for biopsy. To ensure specimen adequacy when immediate specimen evaluation by an on-site cytopathologist is not possible, four samples from predominantly solid nodules and five passes through predominantly cystic nodules are required.