Diagnostic accuracy of ultrasound features in thyroid microcarcinomas.

OBJECTIVE: To establish the usefulness of specific ultrasound (US) features as indications for ultrasound-guided fine needle aspiration biopsy (FNAB) in incidentally found infracentimetric thyroid nodules.

METHODS: The ultrasonographic features and cytology of FNAB samples of 96 histopathologically-proven papillary microcarcinomas (less than 1 cm in long diameter) and 75 less than 1 cm sized benign nodules were analyzed and compared. The risk of malignancy indicated by each US feature was calculated by logistic regression analysis.

RESULTS: Among the US features examined, internal content, shape, margin, echogenicity, and calcifications showed statistically significant differences between benign and malignant infracentimetric nodules. Crude odds ratios (OR) and 95% confidence intervals (CI) for risk of malignancy were, for solid content, OR = 39.3 (95% CI = 3.3-4.64); for taller than wide shape, OR = 14.2 (95% CI = 1.43-14.1); for hypoechogenicity, OR = 3.57 (95% CI = 1.31-9.86); for marked hypoechogenicity, OR = 31.33 (95% CI = 6.63-14.8); and for coarse macrocalcifications, OR = 3.43 (95% CI = 1.04-11.3).

CONCLUSIONS: Infracentimetric nodules that are solid, taller than wide, hypoechogenic or markedly hypoechogenic, and have coarse microcalcifications and macrocalcifications have a high risk of malignancy, indicating further assessment.