Quantitative diffusion-weighted magnetic resonance imaging as a powerful adjunct to fine needle aspiration cytology for assessment of thyroid nodules.

OBJECTIVES: The purpose of this study was to assess the value of the apparent diffusion coefficient (ADC) in the differential diagnosis between benign and malignant thyroid nodules, particularly those found to have indeterminate cytology with fine needle aspiration (FNA). METHODS: Thirty-eight patients with 42 thyroid nodules underwent neck magnetic resonance imaging consisting of T1-, T2-, and diffusion-weighted imaging. The final diagnosis of all nodules was confirmed by surgery, revealing 23 with benign and 19 with malignant lesions. Preoperative FNA cytology was performed in 38 of 42 nodules, including 15 of indeterminate cytology. The mean ADC values in benign and malignant groups were compared. RESULTS: There was a significant difference between mean ADC values in benign and malignant nodules and between mean ADC in benign and malignant nodules of indeterminate cytology. A cutoff value for malignant nodules of 1.60 × 10(-3) mm(2)/s yielded sensitivity, specificity, and accuracy of 94.73%, 82.60%, and 88.09%, respectively. CONCLUSION: The present study revealed that ADC measurements could potentially quantitatively differentiate between benign and malignant thyroid nodules, even those of indeterminate cytology. We propose that diffusion-weighted imaging evaluation should be used for the assessment of thyroid nodules in addition to FNA cytology.