Ultrasound-guided thyroid nodule biopsy: outcomes and correlation with imaging features.

BACKGROUND AND PURPOSE: Thyroid nodules are ubiquitous on ultrasound but have a low risk of malignancy. Hence, risk stratification is essential before biopysing them. We aim to (a) determine the frequency and predictors of nondiagnostic fine needle aspiration biopsy (FNAB) of thyroid nodules and (b) seek correlation between sonographic features and biopsy outcomes.

METHODS: Between January 2010 and April 2013, 559 thyroid nodules underwent ultrasound-guided FNAB. Demographic information was obtained. Prebiopsy ultrasound images were reviewed for size, multiplicity, echotexture, shape, margins, vascularity, calcifications, cervical lymphadenopathy, and extrathyroid extension. Univariate and multivariate logistic regression analyses adjusting for the correlation between multiple nodules obtained from the same patient were performed.

RESULTS: A total of 10.6% of the biopsies were nondiagnostic. Male gender [adjusted odds ratio (OR)=3.78, 95% confidence interval (CI) 1.87-7.66, P<.001] and a taller-than-wide shape (adjusted OR=3.22, 95% CI 1.34-7.75, P=.009) were independent predictors of a nondiagnostic FNAB. There was no significant association with cystic echotexture or a smaller nodule size. Well-defined irregular margins, microcalcifications, and coarse calcifications were independent predictors of malignancy, with specificities above 96% but low sensitivities (59.3%, 44.4%, and 11.1%, respectively). All nodules with cervical lymphadenopathy were malignant. If biopsy is performed when at least one of the above four features are present, the sensitivity, specificity, positive likelihood ratio and negative likelihood ratio of predicting malignancy are 81.5%, 93.1%, 11.8 and 0.2 respectively. All purely cystic nodules and spongiform nodules were benign.

CONCLUSIONS: Male gender and taller-than-wide thyroid nodules are independent risk factors for a nondiagnostic FNAB. Prudent use of a combination of sonographic features can help to risk-stratify thyroid nodules for FNAB and may reduce unwarranted FNABs.