Abstract
Purpose: To evaluate the diagnostic performance of gray-scale ultrasonography (US) and elastography in differentiating benign and malignant thyroid nodules.
Materials and Methods: This was an institutional review board–approved retrospective study with waiver of informed consent. A total of 703 solid thyroid nodules in 676 patients (mean age, 49.7 years; range, 18–79 years) were included; there were 556 women (mean age, 49.5 years; range, 20–74 years) and 120 men (mean age, 50.7 years; range, 18–79 years). Nodules with marked hypoechogenicity, poorly defined margins, microcalcifications, and a taller-than-wide shape were classified as suspicious at grayscale US. Findings at elastography were classified according to the Rago criteria and the Asteria criteria. The diagnostic performances of gray-scale US and elastography were compared. For comparison between the diagnostic performances of gray-scale US and the combination of gray-scale US and elastography, three sets of criteria were assigned: criteria set 1, nodules with any suspicious grayscale US feature were assessed as suspicious; criteria set 2, Rago criteria were added as suspicious features to criteria set 1; and criteria set 3, Asteria criteria were added as suspicious features to criteria set 1. The diagnostic performances of gray-scale US, elastography with Rago criteria, and elastography with Asteria criteria, and odds ratios (ORs) with 95% confidence intervals for predicting thyroid malignancy were compared using generalized estimating equation analysis.
Results: Of 703 nodules, 217 were malignant and 486 were benign. Sensitivity, negative predictive value (NPV), and OR of gray-scale US for the 703 nodules were 91.7%, 94.7%, and 22.1, respectively, and these values were higher than the 15.7% and 65.4% sensitivity, 71.7% and 79.1% NPV, and 3.7 and 2.6 ORs found for elastography with Rago and Asteria criteria, respectively. Specificity, positive predictive value, and accuracy for criteria set 1 were significantly higher than those for criteria sets 2 and 3 for most of the nodule subgroups that were considered.
Conclusion: Elastography alone, as well as the combination of elastography and gray-scale US, showed inferior performance in the differentiation of malignant and benign thyroid nodules compared with gray-scale US features; elastography was not a useful tool in recommending fine-needle aspiration biopsy.
© RSNA, 2012
BACKGROUND
When fine-needle aspiration biopsy of thyroid nodules is performed, approximately one fourth fall into the indeterminate classification. Some authorities recommend surgical removal of all indeterminate nodules, lthough only about 10% to 30% are malignant. Real-time elastography (RTE) has been proposed to improve the diagnosis of thyroid cancer before surgery. Thyroid cancers have a harder consistency than benign thyroid nodules; RTE is a technique that uses ultrasonography to provide an estimation of tissue stiffness by measuring the degree of elasticity under the application of external light force. The goal of the current study was determine the efficacy of RTE, as compared with conventional ultrasonography (US), for differentiating malignant from benign thyroid lesions in patients being operated on for nodules with indeterminate cytology.
METHODS
The study included 102 patients (69 women) with indeterminate cytology who had conventional US and RTE. Elasticity was scored from 1 (elastic) to 4 (stiff). The median nodule diameter was 2.2 cm (range, 0.7 to 10).
RESULTS
All patients underwent surgery; 36 had a pathologic diagnosis of cancer (32 follicular variant of papillary thyroid cancer, 2 classic papillary, and 2 follicular carcinoma). The remaining 66 nodules were benign, with a final pathology of follicular adenoma in 64 and hyperplastic nodule in 2. The only ultrasound feature that was significantly associated with the diagnosis of cancer was microcalcification, and this was found in 56%. Thyroid cancer was detected in 50% of the nodules that scored 1 to 2 on RTE (good elasticity) and in 34% that scored 3 to 4 (stiff). Of the 36 patients with malignant nodules, 32 had RTE scores of 3 to 4.
Although the sensitivity was 89%, the positive predictive value was only 34% and the negative predictive value was 50%.
CONCLUSIONS
The current study did not confirm the utility of RTE for the differential diagnosis of malignancy or benignity in thyroid nodules with indeterminate cytology.
ANALYSIS and COMMENTARY
Investigators from Pisa, Italy, had previously reported that RTE was useful for making a diagnosis of malignancy in indeterminate nodules with a positive predictive value of 77% and a negative predictive value of 99% (1). The cause of the lack of confirmation of this result in the current study is unclear. The person performing RTE in this study was very experienced.
Nevertheless, there is a considerable element of subsoftware has been developed for quantitative analysis of stiffness. One technique, called “shear wave elastography,” may be more useful because it eliminates the operator-dependence of the procedure (2, reviewed in the January 2011 issue of Clinical Thyroidology). It is likely that the true utility of shear wave elastography for discrimination between benign and malignant nodules in the indeterminate category will require additional studies for validation.
— Jerome M. Hershman, MD
REFERENCES
1. Rago T, Scutari M, Santini F, Loiacono V, Piaggi P, Di Coscio G, Basolo F, Berti P, Pinchera A, Vitti P. Real-time elastosonography: useful tool for refining the presurgical diagnosis in thyroid nodules with indeterminate or nondiagnostic cytology. J Clin Endocrinol Metab 2010;95:5274– 5280, Epub September, 2010.
2. Sebag F, Vaillant-Lombard J, Berbis J, Griset V, Henry JF, Petit P, Oliver C. Shear wave elastography: a new ultrasound imaging mode for the differential diagnosis of benign and malignant thyroid nodules. J Clin Endocrinol Metab 2010;95:5281–8. Epub September 29, 2010.
