Use of strain ultrasound elastography versus fine-needle aspiration cytology for the differential diagnosis of thyroid nodules: a retrospective analysis

Abstract

Objective: Fine-needle aspiration cytology is the risk stratification tool for thyroid nodules, and ultrasound elastography is not routinely used for the differential diagnosis of thyroid cancer. The current study aimed to compare the diagnostic parameters of ultrasound elastography and fine-needle aspiration cytology, using surgical pathology as the reference standard.

Methods: In total, 205 patients with abnormal thyroid function test results underwent ultrasound-guided fine-needle aspiration cytology on the basis of the American College of Radiology Thyroid Imaging-Reporting and Data System classification and strain ultrasound elastography according to the ASTERIA criteria. Histopathological examination of the surgical specimens was performed according to the 2017 World Health Organization classification system. Moreover, a beneficial score analysis for each modality was conducted.

Results: Of 265 nodules, 212 measured ≥1 cm. The strain index value increased from benign to malignant nodules, and the presence of autoimmune thyroid diseases did not affect the results (p>0.05 for all categories). The sensitivities of histopathological examination, ultrasound elastography, and fine-needle aspiration cytology for detection of nodules measuring ≥1 cm were 1, 1, and 0.97, respectively. The working area for detecting nodule(s) in a single image was similar between strain ultrasound elastography and fine-needle aspiration cytology for highly and moderately suspicious nodules. However, for mildly suspicious, unsuspicious, and benign nodules, the working area for detecting nodule(s) in a single image was higher in strain ultrasound elastography than in fine-needle aspiration cytology.

Conclusion: Strain ultrasound elastography for highly and moderately suspicious nodules facilitated the detection of mildly suspicious, unsuspicious, and benign nodules.

Figure 1. Flow diagram of the study.

Figure 2. Strain ultrasound elastography. 1: The examined area was homogenously green (elasticity in the whole area examined; benign nodule), 2: the examined area was light green and red with peripheral and central blue mass (the elasticity in the large portion of the examined area; indeterminate follicular lesion), 3: the examined area was blue with some light green and red mass (the large portion of nodule with stiffness; nodule suspicious for malignancy), 4: the area was homogeneously blue (non-elastic nodule; malignant nodule). A: Real-time ultrasound evaluations. B: Ultrasound elastography evaluation. Real-time ultrasonography and ultrasound elastography were performed by ultrasound technologists with a minimum experience of 5 years.

Figure 3. Determination of the strain index of a 42-year-old male patient with abnormal thyroid function test result. The B-to-A ratio was the strain index. X: Real-time ultrasonography. Y: Ultrasound elastography evaluation. B: Thyroid nodule strain. A: The strain of the softest area of the parenchyma. Real-time ultrasonography and ultrasound elastography were performed by ultrasound technologists with a minimum experience of 5 years.

Figure 4. Distribution of the strain index according to the different categories of nodules. The ratio of thyroid nodule strain to the strain of the softest area of the parenchyma was considered the strain index. Ultrasound elastography was performed by ultrasound technologists with a minimum experience of 5 years.

Figure 5. Beneficial score analysis. Pathologist with a minimum experience of 3 years performed the cytological and histopathological examinations. Ultrasound technologists with a minimum experience of 5 years in thyroid imaging conducted real-time ultrasonography and ultrasound elastography.