Differentiation between benign and malignant solid thyroid nodules using an US classification system

Abstract

Objective: To evaluate the diagnostic accuracy of a new ultrasound (US) classification system for differentiating between benign and malignant solid thyroid nodules.

Materials and methods: In this study, we enrolled 191 consecutive patients who received real-time US and subsequent US diagnoses for solid thyroid nodules, and underwent US-guided fine-needle aspiration. Each thyroid nodule was prospectively classified into 1 of 5 diagnostic categories by real-time US: "malignant," "suspicious for malignancy," "borderline," "probably benign," and "benign". We evaluated the diagnostic accuracy of thyroid US and the cut-off US criteria by comparing the US diagnoses of thyroid nodules with cytopathologic results.

Results: Of the 191 solid nodules, 103 were subjected to thyroid surgery. US categories for these 191 nodules were malignant (n = 52), suspicious for malignancy (n = 16), borderline (n = 23), probably benign (n = 18), and benign (n = 82). A receiver-operating characteristic curve analysis revealed that the US diagnosis for solid thyroid nodules using the 5-category US classification system was very good. The sensitivity, specificity, positive and negative predictive values, and accuracy of US diagnosis were 86%, 95%, 91%, 92%, and 92%, respectively, when benign, probably benign, and borderline categories were collectively classified as benign (negative).

Conclusion: The diagnostic accuracy of thyroid US for solid thyroid nodules is high when the above-mentioned US classification system is applied.

Keywords: Classification; Fine-needle aspiration; Malignancy; Solid, Ultrasound; Thyroid nodule.

Fig. 1

Five categories for US diagnosis of solid thyroid nodules. A. Malignant. Longitudinal US image of papillary thyroid carcinoma in 42-year-old woman shows marked hypoechogenicity, spiculated margin, microcalcifications, and taller-than-wide shape for nodule. B. Suspicious for malignancy. Longitudinal US image of papillary thyroid carcinoma in 42-year-old woman shows marked hypoechogenicity, smooth margin, and ovoid shape. C. Borderline. Transverse US image of nodular hyperplasia in 60-year-old woman shows macrocalcification in peripheral portion of nodule. Patient underwent right lobectomy of thyroid, despite benign cytology upon US-guided fine-needle aspiration, for pathologic confirmation. D. Probably benign. Longitudinal US image of benign nodule in 57-year-old woman shows isoechogenicity and smooth margin. E. Benign. Longitudinal US image of benign nodule in 46-year-old woman shows ovoid shape, isoechogenicity, and smooth margin.

Fig. 2

Metastatic lymphadenopathy of papillary thyroid carcinoma in perithyroidal region. Transverse US image in 27-year-old woman shows associated lymph nodes (arrows) with intranodal cystic components (arrowheads) along both tracheoesophageal grooves in level of upper trachea.

Fig. 3

US classification system with 5 categories for diagnosis of solid thyroid nodules.

Fig. 4

Receiver-operating characteristic (ROC) analysis. A. Receiver-operating characteristic curves for cut-off US criteria of malignancy. When nodules having 1, 2, or 3 or more malignant US features were considered malignant, Az values were 0.940 (dotted line), 0.950 (dashed line), and 0.931 (dotted and dashed line), respectively. B. Receiver-operating characteristic curve of US classification system when two or more malignant US features were considered as criteria of malignant US diagnosis (Az value: 0.950, confidence interval: 0.914-0.986). Sensitivity, specificity, positive and negative predictive values, and accuracy of US diagnosis were determined to be 86%, 95%, 91%, 92%, and 92%, respectively when malignant and suspicious for malignancy cases were collectively classified as malignant and benign, while probably benign and borderline were collectively classified as benign.

Fig. 5

Benign nodule designated as suspicious for malignancy as result of thyroid US in 52-year-old woman (false positive). Longitudinal US image of thyroid nodule in left mid-lobe shows hypoechogenicity, spiculated margin, and round shape (arrow); however, lesion was confirmed as spontaneously collapsed nodule of previous benign cystic thyroid nodule by consecutive US-fine needle aspirations and follow-up US.

Fig. 6

Papillary thyroid carcinoma designated as benign from thyroid US in 18-year-old woman (false negative). Longitudinal US image of right thyroid nodule shows ovoid shape, isoechogenicity, smooth margin, and peripheral vascularity (A, B).