A Risk Model for Predicting Central Lymph Node Metastasis of Papillary Thyroid Microcarcinoma Including Conventional Ultrasound and Acoustic Radiation Force Impulse Elastography

Abstract

The aim of this prospective study was to propose a new rating system using a risk model including conventional ultrasound (US) and acoustic radiation force impulse (ARFI) elastography for predicting central lymph node metastasis (LNM) in patients with papillary thyroid microcarcinoma (PTMC).A total of 252 patients with PTMCs were enrolled, who were preoperatively evaluated by US and ARFI elastography including virtual touch tissue imaging (VTI) and virtual touch tissue quantification (VTQ). Risk factors of independent variables for central LNM were analyzed by univariate and multivariate analyses. A multivariate analysis was performed to create a predicting model and rating system.Of the 252 patients, 72 (28.6%) had central LNMs. Multivariate analysis revealed that rare internal flow (odds ratio [OR]: 4.454), multiple suspicious foci on US (OR: 5.136), capsule involvement (OR: 20.632), and VTI area ratio (VAR) > 1 (OR: 5.621) were independent risk factors for central LNM. The final predicting model was obtained and the risk score (RS) was defined as 1.5 × (if rare internal flow) + 1.6 × (if multiple suspicious foci on US) + 1.7 × (if VAR > 1) + 3.0 × (if capsule involvement). The rating system was divided into 5 stages. Stage I, <1.5; Stage II, 1.5 to 3.0; Stage III, 3.1 to 4.7; Stage IV, 4.8 to 6.3; and Stage V, 6.4 to 7.8. The risk rates of central LNM were 3.4% (2/59) in Stage I, 13.3% (13/98) in Stage II, 54.2% (39/72) in Stage III, 72.2% (13/18) in Stage IV, and 100% (5/5) in Stage V (P < 0.001).The results indicated that rare internal flow, multiple suspicious foci, capsule involvement on US, and VAR > 1 on ARFI elastography are the risk factors for predicting central LNM. The risk model developed in the study clearly predicts the risk of central LNM in patients with PTMC and thus has a potential to avoid unnecessary central compartment node dissection.

Association Between Preoperative US, Elastography Features and Prognostic Factors of Papillary Thyroid Cancer With BRAFV600E Mutation

“…As clinical important supplementary technique, US features of thyroid nodules in evaluating the malignancy have already been determined (12,20,28,29). However, the relation of preoperative US findings and prognosis was reported few (15)(16)(17). In the preoperative US, we found that rich internal flow (OR: 6.66, P = 0.002) was the strongest independent factors to predict central LNM and ETE, although the sensitivities (42.5-42.9%) and specificities (74.3-76.7%) were moderate.…”

“…The white scale indicated that areas were greatest strain (i.e., softest component); correspondingly, the black scale indicated that areas were less or no strain (i.e., hardest component). According to the Xu's VTI grading method, VTI images were divided into 6 grades (15,16,20,21). The stiffness of tissue was more likely to be hard, when the grade of VTI images increased.…”

“…The stiffness of tissue was more likely to be hard, when the grade of VTI images increased. In addition, the VTI area ratio (VAR) of the tumors was calculated and defined as the area of the tumor on VTI image divided by the area on US image (15,16,22).…”

“…The sensitivity and specificity in detecting cervical LNM by US are superior to those by palpation (12,13), although the value of diagnosis is moderate (36-72%) in clinical node-negative PTC (14). Recently, some authors reported that absence of thyroid capsule and contact with capsule on US were the independent risk factors for cervical LNM or ETE, but the related features were not evaluated in high-risk PTC patients (15)(16)(17). Based on the association between tumor stiffness and clinic pathologic characteristics, US elastic imaging (EI) was also found to be a useful technology for predicting ETE and cervical LNM (18,19).…”

“…Consequently, operator-independence and reproducible of ARFI are more superior to those of conventional EI (16,23,24). Although ARFI imaging is useful in predicting cervical LNM (15,16), there are no studies on the association between ARFI imaging findings and prognosis in the positive BRAF V600E Mutation group. Herein we hypothesized that ARFI imaging might be useful in predicting poor prognosis in the high-risk PTC group.…”