To assess the value of ultrasonography in the diagnosis and differential diagnosis of primary thyroid lymphoma (PTL) and anaplastic thyroid carcinoma (ATC).

The clinical, pathological, and ultrasonic manifestations of 73 cases of PTL and 28 cases of ATC were analyzed retrospectively at West China Hospital of Sichuan University from September 2004 to November 2019. For numerical data such as age, maximum diameter of the lesion, the maximum (Emax) and minimum (Emin) values of Young's modulus, mean (Emean) value of Young's modulus, and the ratio between elastic evaluation values of thyroid lesion and normal tissue (Ratio), t-test or Mann Whitney U test was used for comparisons between groups. Gender, clinical symptoms, ultrasound classification, morphology, blood flow classification, enhancement degree, and other count data were compared between groups by chi square test or Fisher exact test. Logistic regression analysis was used to analyze the dominant parameters of shear wave elastography (SWE) in the diagnosis of PTL and ATC, and the ROC curve of the dominant parameters was analyzed. In addition, the proportion of each pathological subtype of PTL was compared, and the two most common pathological types of ultrasound classification, morphology, blood flow classification, and other count data were compared by chi square test or Fisher exact test.

Hoarseness occurred significantly more frequently in ATC than in PTL (28.6% vs 5.5%, χ²=8.220, P=0.004), while there was no significant difference in age, gender, short-term enlargement of neck mass, dyspnea, or dysphagia (P＞0.05 for all). The largest diameter of PTL lesion was larger than that of ATC [43.50 (42.50) mm vs 26.00 (26.00) mm, Z=2.636, P=0.008]. The background proportion of acoustic enhancement and concomitant chronic thyroiditis was higher in PTL than in ATC (60.3% vs 21.4%, χ²=12.439, P=0.002; 45.2% vs 0, χ²=25.128, P＜0.001; 97.3% vs 3.6%, χ²=86.786, P＜0.001). The rates of nodular type, irregular morphology, indistinct margins, internal hypoechogenicity, and calcification were significantly higher in ATC than in PTL (100% vs 68.5%, χ²=12.294, P=0.001; 96.4% vs 69.9%, χ²=8.121, P=0.004; 82.1% vs 56.2%, χ²=5.884, P=0.015; 64.3% vs 34.2%,χ²=12.439, P =0.002; 60.7% vs 2.7%, χ²=44.536, P＜0.001). The most common Adler flow grade was grade 2, which was not significantly different between the two entities (P＞0.05). Neither the degree of enhancement nor the perfusion defect was significantly different between ATC and PTL (P＞0.05). Emin was significantly smaller in PTL than in ATC [3.70 (8.85) kPa vs 25.60 (17.90) kPa, Z=2.591, P=0.010], while Emean, Emax, and Ratio were not significantly different between the two entities (P＞0.05 for all). Logistic regression analysis showed that Emin was independently correlated with the diagnosis of PTL and ATC. The ROC curve of Emin was drawn; the area under the ROC curve was 0.863, the maximum Youden index was 0.774, and the corresponding cut-off value was 11.950 kPa, with a sensitivity and specificity of 85.7% and 91.7%, respectively. In this study, there were eight pathologic subtypes of PTL, with the most common being diffuse large B-cell lymphoma (DLBCL), followed by mucosa associated lymphoid tissue extranodal marginal zone B-cell lymphoma (MALT). DLBCL was characterized by nodular type, indistinct margins, irregular morphology, heterogeneous hypoechogenicity, and higher proportion of grade 2 Adler blood flow than that in MALT (72.5% vs 33.3%, χ²=15.190, P＜0.001; 65.0% vs 38.1%, χ²=4.040, P=0.044; 87.5% vs 33.3%, χ²=18.840, P＜0.001; 67.5% vs 38.1%, χ²=9.273, P=0.007; 60.0% vs 19.0%, χ²=17.693, P＜0.001), but there was no significant difference in the posterior echo characteristics (P＞0.05).

Both PTL and ATC have characteristic ultrasonographic findings. Ultrasound is helpful in their diagnosis and differential diagnosis.