Original ContributionUltrasound Elastography for Thyroid Nodules: A Reliable Study?
Introduction
Ultrasound elastography (USE) measures tissue deformation in response to compression and displays tissue stiffness (Lerner et al. 1990; Ophir et al. 1991; Gao et al. 1996; Ophir et al. 1999; Greenleaf et al. 2003). USE is useful in differentiating between benign and malignant tumors of breast, prostate and thyroid gland (Garra et al. 1997; Cochlin et al. 2002; Thomas et al. 2006; Pallwein et al. 2007). The sensitivity and specificity of USE for differentiating thyroid nodules have been reported to be 82%–97% and 77.5%–100%, respectively (Lyshchik et al. 2005; Rago et al. 2007; Asteria et al. 2008; Dighe et al. 2008; Hong et al. 2009) and are, therefore, superior to the respective values of 83.3% and 74% reported for grayscale ultrasound (US) (Moon et al. 2008). However, Kagoya et al. demonstrated high sensitivity (90%) but low specificity (50%) and Park et al. found a lack of reliable interobserver agreement for USE compared with grayscale US in the diagnosis of malignant thyroid nodules (Park et al. 2009; Kagoya et al. 2010). These results suggest that interpretation of the results of USE can be subjective.
Various factors may influence the rating elasticity score, such as nodule size, exophytic location, rim calcification, thyroiditis and motion artifacts (Lyshchik et al. 2005; Rago et al. 2007; Asteria et al. 2008; Dighe et al. 2008; Hong et al. 2009). In a study by Hong et al., incorrect USE results were obtained with nodules protruding from the thyroid capsule (Hong et al. 2009). Many authors agree that coarse or peripheral rim calcifications cause an incorrect USE results (Lyshchik et al. 2005; Rago et al. 2007; Asteria et al. 2008; Hong et al. 2009). Calcifications within nodules increase nodular stiffness and, thus, probe compression does not result in tissue strain deformation (Asteria et al. 2008). Hong et al. suggested that two nodules in patients with subacute thyroiditis showed malignant USE finding (Hong et al. 2009). However, Dighe et al. reported benign USE results in four patients with lymphocytic thyroiditis (Dighe et al. 2008). Several factors such as those secondary to pulsation of the carotid artery, out-of-plane motion, swallowing and breathing have also been proposed as causes of incorrect USE results (Lyshchik et al. 2005; Asteria et al. 2008).
Investigators may vary in their rating of elasticity, a measure that is influenced by several factors. Repeated examination may, therefore, fail to generate reliable elasticity scores. The purpose of the present study was threefold: (1) to evaluate the reliability of USE; (2) to determine the factors affecting reliability; and (3) to assess interobserver and intraobserver agreement concerning reliability.
Section snippets
Patients
The protocol of the present retrospective study was approved by Institutional Review Board of Asan Medical Center and neither patient approval nor informed consent was required for the review of images and clinical records. Informed consent had been obtained from all patients prior to the performance of US-guided fine needle aspiration cytology (FNAC).
US-guided FNAC was performed for 132 thyroid nodules in 97 consecutive patients between September, 2009 and October, 2009. This study was
Results
Among the 78 patients, 53 patients had one nodule, 22 patients had two nodules and three patients had three nodules. The mean diameter of the thyroid nodules was 1.2 ± 1.0 cm (range, 0.3–5.7 cm).
Consensual reliability of USE was 68% (72/106). A total of 32% (34/106) of the thyroid nodules showed less reliable results. The causes of less reliable results were as follows: (1) <50% green color in the ROI box for the thyroid parenchyma (n = 13) (Fig. 1); (2) discordance in elasticity scores in the
Discussion
The present study demonstrated that reliable USE results were obtained for 68% of the nodules and these were significantly associated with nodule motion, rim calcification and compressive force. For nodules showing reliable USE results, interobserver and intraobserver agreement was substantial. This result, therefore, differs from that of Park et al. (Park et al. 2009), who assessed interobserver agreement for all thyroid nodules, irrespective of the reliability of the USE result.
Many
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