Interobserver agreement of Thyroid Imaging Reporting and Data System (TIRADS) and strain elastography for the assessment of thyroid nodules

Background: Thyroid Imaging Reporting and Data System (TIRADS) was developed to improve patient management and cost-effectiveness by avoiding unnecessary fine needle aspiration biopsy (FNAB) in patients with thyroid nodules. However, its clinical use is still very limited. Strain elastography (SE) enables the determination of tissue elasticity and has shown promising results for the differentiation of thyroid nodules. Methods: The aim of the present study was to evaluate the interobserver agreement (IA) of TIRADS developed by Horvath et al. and SE. Three blinded observers independently scored stored images of TIRADS and SE in 114 thyroid nodules (114 patients). Cytology and/or histology was available for all benign (n = 99) and histology for all malignant nodules (n = 15). Results: The IA between the 3 observers was only fair for TIRADS categories 2–5 (Coheńs kappa = 0.27,p = 0.000001) and TIRADS categories 2/3 versus 4/5 (ck = 0.25,p = 0.0020). The IA was substantial for SE scores 1–4 (ck = 0.66,p<0.000001) and very good for SE scores 1/2 versus 3/4 (ck = 0.81,p<0.000001). 92–100% of patients with TIRADS-2 had benign lesions, while 28–42% with TIRADS-5 had malignant cytology/histology. The negative-predictive-value (NPV) was 92–100% for TIRADS using TIRADS-categories 4&5 and 96–98% for SE using score ES-3&4 for the diagnosis of malignancy, respectively. However, only 11–42% of nodules were in TIRADS-categories 2&3, as compared to 58–60% with ES-1&2. Conclusions: IA of TIRADS developed by Horvath et al. is only fair. TIRADS and SE have high NPV for excluding malignancy in the diagnostic work-up of thyroid nodules

Acoustic radiation force impulse imaging for differentiation of thyroid nodules

Background: Acoustic Radiation Force Impulse (ARFI)-imaging is an ultrasound-based elastography method enabling quantitative measurement of tissue stiffness. The aim of the present study was to evaluate sensitivity and specificity of ARFI-imaging for differentiation of thyroid nodules and to compare it to the well evaluated qualitative real-time elastography (RTE). Methods: ARFI-imaging involves the mechanical excitation of tissue using acoustic pulses to generate localized displacements resulting in shear-wave propagation which is tracked using correlation-based methods and recorded in m/s. Inclusion criteria were: nodules $5 mm, and cytological/histological assessment. All patients received conventional ultrasound, real-time elastography (RTE) and ARFI-imaging. Results: One-hundred-fifty-eight nodules in 138 patients were available for analysis. One-hundred-thirty-seven nodules were benign on cytology/histology, and twenty-one nodules were malignant. The median velocity of ARFI-imaging in the healthy thyroid tissue, as well as in benign and malignant thyroid nodules was 1.76 m/s, 1.90 m/s, and 2.69 m/s, respectively. While no significant difference in median velocity was found between healthy thyroid tissue and benign thyroid nodules, a significant difference was found between malignant thyroid nodules on the one hand and healthy thyroid tissue (p = 0.0019) or benign thyroid nodules (p = 0.0039) on the other hand. No significant difference of diagnostic accuracy for the diagnosis of malignant thyroid nodules was found between RTE and ARFI-imaging (0.74 vs. 0.69, p = 0.54). The combination of RTE with ARFI did not improve diagnostic accuracy. Conclusions: ARFI can be used as an additional tool in the diagnostic work up of thyroid nodules with high negative predictive value and comparable results to RTE

Example of TIRADS and SE of thyroid adenoma: 10 mm nodule in the right thyroid gland classified as TIRADS 4 (consistent with malignancy) in the left image and SE 2 (predominantly green = soft; consistent with benign nodule) in the right image.

<p>Histology revealed a benign follicular thyroid adenoma.</p

Patient characteristics.

<p><i>SD  =  standard deviation</i>, * 21 patients received cytology first and were operated thereafter, therefore cytology and histology was available in these patients.</p

Example of TIRADS and SE of papillary carcinoma: 10 mm nodule in the right thyroid gland classified as TIRADS 4 (consistent with malignancy) in the left image and SE 3 (predominantly blue = hard; consistent with malignancy) in the right image.

<p>Histology revealed a papillary T2 carcinoma.</p

Diagnostic value of TIRADS and SE for the diagnosis of malignant thyroid nodules.

<p>Diagnostic value of TIRADS and SE for the diagnosis of malignant thyroid nodules.</p

B-mode ultrasound of the right lobe of thyroid gland using the S2000, 9L4 probe at 9 MHz with the ROI placed within the healthy thyroid tissue measuring an ARFI velocity of 1.90 m/s.

<p>B-mode ultrasound of the right lobe of thyroid gland using the S2000, 9L4 probe at 9 MHz with the ROI placed within the healthy thyroid tissue measuring an ARFI velocity of 1.90 m/s.</p

Acoustic Radiation Force Impulse Imaging (S2000, 9L4 probe at 9 MHz) of the same patient a in

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042735#pone-0042735-g001" target="_blank"><b>Figure 1</b></a><b>with the ROI placed within a hypoechoic thyroid nodule in the right thyroid lobe measuring a velocity of 6.24 m/s.</b> Histology revealed papillary carcinoma.</p