Role of U/S Elastography in Diagnosis of Thyroid Nodules

Abstract

Thyroid nodules are very common and are found in 4% to 8% of adults by palpation, 41% by ultrasound, and 50% by pathologic examination at autopsy. Most nodules are benign, with less than 5% of them being malignant. Cytological examination of material obtained by fine needle aspiration (FNA), due to its high sensitivity and specificity, is the best single test for differentiating malignant from benign thyroid lesions. Yet, a substantial proportion of nodules are not correctly diagnosed before surgical treatment, and histological examination is required. Sonography has many favourable features, such as detection of non palpable nodules, estimation of nodule size/goiter volume, and guidance for fine needle biopsy (FNB). High-resolution ultrasound is very sensitive in detection of thyroid nodules, enabling differentiation of solid and liquid lesions. Ultrasound features indicative of malignant nodule include the presence of irregular margins, marked hypoechogenicity, microcalcifications, taller than wide nodule and intranodular vascularity. Although the strongest independent factor related to malignancy was the absence of surrounding halo sign. The principle of USE is to acquire two ultrasonographic images (before and after tissue compression by the probe), and to track tissue displacement by assessing the propagation of the US beam by a dedicated software. The US elastogram was displayed over the B-mode image in a color scale that ranged from red, for components with greatest elastic strain (i.e. softer components), to blue for those with no strain (i.e. harder components). The purpose of this study was to evaluate indeterminate thyroid nodules by US elastography. In this study, 30 cases were included. The cases were subjected to complete U/S, Colour Doppler examination, and US elastography the results were compared to U/S guided FNAC. Strain elastography involves two kinds of elasticity assessments; realtime visual scoring of colour within and around the nodule and calculation of strain ratio between two regions of interests, within the nodule and within the surrounding. The likelihood of malignancy increases with the increase in strain ratio. When using the best cut off value of strain colour code 3, we found that elasticity imaging is significantly higher in malignant nodules than in benign nodules and normal thyroid tissue with sensitivity and specificity were 91% and 72% respectively. On the off line processed elastograms a strain index higher than 1.6 was shown to be an independent predictor of thyroid malignancy with sensitivity and specificity were 89% and 70% respectively.