Optimal needle size for thyroid fine needle aspiration cytology

Concerning the needle size for thyroid fine needle aspiration cytology (FNAC), 25-27-gauge needles are generally used in Western countries. However, in Japan, the use of larger needles (21-22-gauge needles) is common. The aim of our study was to determine the optimal needle size for thyroid FNAC. We performed ultrasound-guided FNAC for 200 thyroid nodules in 200 patients using two different-sized needles (22 and 25 gauge). For each nodule, two passes with the different-sized needles were performed. The order of needle sizes was reversed for the second group of 100 nodules. The second aspiration was more painful than the first, regardless of the needle size. An association with more severe blood contamination was more frequently observed with the use of 22-gauge needles (32.0%) than with the use of 25-gauge needles (17.5%) and in the second aspiration (37.5%) than in the initial aspiration (12.0%). The initial aspiration samples were more cellular than the second aspiration samples. Regarding the unsatisfactory and malignancy detection rates, there was no statistical difference between the needles. In three of seven markedly calcified nodules, it was difficult to insert 25-gauge needles into the nodules. In terms of the diagnostic accuracy and pain, either needle size can be used. We recommend using 22-gauge needles for markedly calcified nodules because 25-gauge needles bend more easily in such cases. We demonstrated that the initial aspiration tended to obtain more cellular samples and to be less contaminated. Thus, the initial aspiration is more important and should be closely attended.