Relative proportions of stromal to cellular components of pleomorphic adenomas: determination with shear wave elastography.

OBJECTIVES

The purpose of this study was to evaluate whether the relative proportions of stromal to cellular components of pleomorphic adenomas have an effect on the shear elastic modulus determined by shear wave elastography (SWE).

METHODS

This study was approved by the Ethics Committee of our institution and performed between September 2011 and December 2012. Thirty-five patients who underwent surgery for a parotid mass were included in the study. The maximum shear elastic modulus of the mass was measured by SWE. Pleomorphic adenomas were histopathologically subdivided into stroma-poor, intermediate-stroma, and stroma-rich tumors based on the relative proportion of stromal to cellular components.

RESULTS

The maximum shear elastic modulus values of the pleomorphic adenomas ranged from 12.6 to 291.9 kPa (mean ± SD, 120.9 ± 92.8 kPa). The Friedman test revealed a statistically significant relationship between the stromal amount and maximum shear elastic modulus (P < .001). Stroma-poor adenomas (mean, 32.3 ± 27.7 kPa; range, 12.6-81.1 kPa) were softer on SWE than stroma-rich adenomas (mean, 174.1 ± 48.4 kPa; range, 92.7-217.2 kPa; P = .009). No such significant difference was detected between stroma-poor and intermediate-stroma tumors (mean, 146.3 ± 106.1 kPa; range, 19.1-291.9 kPa; P = .062) or between intermediate-stroma and stroma-rich tumors (P = .465).

CONCLUSIONS

Shear wave elastography depicts pleomorphic adenomas with a variable appearance, which is due to the relative proportions of stromal to cellular contents in the tumors.