Differentiating cervical metastatic lymphadenopathy and lymphoma by shear wave elastography

Abstract

Shear wave elastography (SWE) is a recent technological advance of ultrasonography (US) to assess tissue stiffness. The purpose of this study is to assess tissue stiffness of malignant cervical lymph nodes (LN) with SWE, to reveal diagnostic performance of SWE in differentiating metastatic LN from lymphoma, and to assess inter-observer agreement of SWE. We assessed 62 malignant LN (24 lymphomas and 38 metastatic LN) and their median speed was 6.34 m/s and median elasticity was 69.7 kPa. Add of SWE with conventional US improved diagnostic accuracy of differentiating metastasis from lymphoma (16.13, 8.07 and 11.3% for three radiologists). Kendall's Coefficient of Concordance of three readers for analyzing SWE patterns was 0.86. SWE can be a useful tool to discriminate metastatic cervical LN from lymphoma with improvement of diagnostic accuracy when using with conventional US.

Figure 1

(a~d) Results of absolute and relative values of shear wave elastography. (a) Absolute elasticity of metastasis (Elasticity_M) was significantly higher than that of lymphoma (Elasticity_L). One case of metastasis from lung adenocarcinoma was an outlier. (b) Relative elasticity of metastasis (R. Elasticity_M) was significantly higher than that of lymphoma (R. Elasticity_L). Two cases of diffuse large B cell lymphoma were outliers. (c) Absolute speed of metastasis (Speed_M) was significantly higher than that of lymphoma (Speed_L). (d) Relative speed of metastasis (R. speed_M) was significantly higher than that of lymphoma (R. speed_L). Among these four plots, absolute speed has the least overlapping feature. Boxes and whiskers plots express medians, interquartile and overall ranges. The outlying values are plotted individually.

Figure 2

(a~e) Schematic drawings of five patterns shear wave elastography. We categorized total five SWE patterns of shear wave speed maps. In cervical lymph nodes (green dotted lines). (a) The pattern 1 nodes have absent or very small red (stiff) area; (b) the pattern 2 nodes have small scattered red areas, which mean total red area less than 45%; (c) the pattern 3 nodes have large red area, equal or more than 45%; (d) the pattern 4 nodes show peripheral red are and central green (soft) area, suggesting central necrosis; and (e) the pattern 5 nodes appear as almost red area with or without a green rim. (f~j) The examples of pattern analysis. (f) The pattern 1: diffuse large B cell lymphoma; (g) the pattern 2: T-cell/histiocyte rich large B cell lymphoma; (h) the pattern 3: metastatic squamous cell carcinoma from nasopharynx; (i) the pattern 4: metastatic adenocarcinoma from lung; and (j) the pattern 5: metastasis from papillary thyroid carcinoma

Figure 3

ROC curves of shear wave elastography. ROC analysis was performed to obtain the best value for differentiating metastasis from lymphoma. The AUC values by max elasticity (a blue line), relative elasticity (a green line), max speed (a gold line) and relative speed (a purple line) were 82.1, 80.8, 85.8 and 83.33, respectively. The cut-off vaule of relative speed had the largest AUC and it was 1.915 (p < 0.001).

Figure 4

The case of diffuse large B cell lymphoma. On conventional ultrasound (a: 2D echo, b: power Doppler US), multiple round lymph nodes have heterogeneous echogenicity and show indistinct border with internal mixed vascularity. Two readers diagnosed these lymph nodes as metastasis with 2D and Doppler US. After evaluation with shear wave elastography (c: the elasticity map, d: the speed map), all readers classified the nodes as pattern 2, and the two readers corrected their diagnosis as lymphoma. Maximum elasticity, relative elasticity, maximum speed and relative speed were 30.4 kPa, 1.32, 3.16 m/s and 1.16, respectively.

Figure 5

The case of metastatic squamous cell from lung. On conventional ultrasound (a: 2D echo, b: power Doppler US), an oval lymph node with loss of hilum has relatively homogeneous high internal echogenicity and shows regular border with internal mixed vascularity. Two readers diagnosed these lymph nodes as lymphoma with 2D and Doppler US. After evaluation with shear wave elastography (c: the elasticity map, d: the speed map), all readers classified the nodes as pattern 3, and the two readers corrected their diagnosis as metastasis. Maximum elasticity, relative elasticity, maximum speed and relative speed were 92.3 kPa, 7.1, 7 m/s and 3.44, respectively.