Grey-scale analysis in the ultrasonographic evaluation of thyroid nodules

Objective: Subjective analysis of ultrasonography (US) images is the first-line method to assess thyroid nodules, although it is limited by inter-observer variability and experience. The purpose of this study is to perform a quantitative measurement of echogenicity and echo-pattern, obtaining an objective estimate of the degree of hypoechogenicity and homogeneity, associated with risk of malignancy. Methods: From January 2010 to October 2012, 839 consecutive patients (908 nodules) underwent US-guided FNA. In a single US image, three regions of interest (ROIs) were drawn: the first including the nodule; the second included a portion of the adjacent thyroid parenchyma; the third, the strap muscle. Histogram analysis was performed, obtaining the median, mean and SD of the pixels comprising each ROI. Echogenicity was expressed as a ratio: the nodule/parenchyma and parenchyma/muscle median grey ratios were calculated. The heterogeneity index was calculated as the coefficient of variation o

Objective: Subjective analysis of ultrasonography (US) images is the first-line method to assess thyroid nodules, although it is limited by inter-observer variability and experience. The purpose of this study is to perform a quantitative measurement of echogenicity and echo-pattern, obtaining an objective estimate of the degree of hypoechogenicity and homogeneity, associated with risk of malignancy. Methods: From January 2010 to October 2012, 839 consecutive patients (908 nodules) underwent US-guided FNA. In a single US image, three regions of interest (ROIs) were drawn: the first including the nodule; the second included a portion of the adjacent thyroid parenchyma; the third, the strap muscle. Histogram analysis was performed, obtaining the median, mean and SD of the pixels comprising each ROI. Echogenicity was expressed as a ratio: the nodule/parenchyma and parenchyma/muscle median grey ratios were calculated. The heterogeneity index was calculated as the coefficient of variation of grey histogram for each of the three ROIs. Results or Case Presentation: Nodule/parenchyma median grey ratio was significantly lower (more hypoechoic) in nodules found to be suspicious for cancer, according to the cytology report (p=0.006) and in confirmed malignant nodules (p=0.02). A nodule/parenchyma median grey ratio <0.46 has a sensitivity of 53.6% and specificity of 71.1% in predicting malignancy (OR 2.84; p=0.01). It can also be used as a continuous measure of hypoechogenicity and risk of malignancy (OR 0.20; p=0.02). Discussion: US is a widely available and harmless method. It nonetheless is operator-dependent. The inter-observer agreement seems to be relatively good; however, a merely slight agreement was reported for echogenicity and echotexture. We developed a method to perform a quantitative measurement of thyroid echogenicity, avoiding the need for fixed US operating conditions. Conclusion: Evaluation of nodule echogenicity according to the nodule/parenchyma median grey ratio allows for an objective stratification of thyroid nodule structure and risk of malignancy.