Purpose: To evaluate main factors which lead to inadequate sampling in ultrasound (US)-guided fine needle aspiration biopsy of thyroid gland.
Materials and Methods: From February 2007 to May 2007, consecutive 1558 cases of US-guided thyroid fine needle aspiration biopsy (FNAB) in 1430 patients (M: 176, F: 1254, age:11-83 year) were reviewed. Univariate statistical analysis was done for evaluating the effects of multiple factors; size, gender, composition, echogenicity, margin, type of calcification, shape, thyroid parenchymal echogenicity, pattern of vascularity, FNAB technique, performing doctor, level of doctor’s experience, US assessment category, and final op. pathology.
Results: The cytological results of FNAB were as followed; benign (856, 54.94%), malignant (262, 16.82%), indeterminate (238, 15.28%), and inadequate samples (202, 12.96%). In the univariate analysis, it showed statistically significant (p=0.02, p=0.05 and p<0.0001, respectively) for the following facts: 1) echogenicity, 2) calcification, 3) final op pathology. In sub categorized calcifications, macro- puls eggshell calcification group and eggshell calcification were more significant than others (p=0.02 and p=0.01). Among them malignant lesion on final op. pathology was the strong contributor. However, the following factors did not make significant effects (p=0.06, p=0.70, p=0.65, p=0.74, p=0.97, p=0.18, p=0.41, p=0.65, p=0.12 and p=0.07 respectively): size, performing doctor, faculty vs. trainee group, aspiration technique, composition, margin, shape, parenchymal echogenicity, vascularity and final assessment.
Conclusion: Marked hypoechogenic nodule and malignant nodule tend to make more adequate FNAB samples, compared with others. On the other hand, inadequate sampling is more common in the nodule with eggshell or macro-calcification.