MR elastography in patients with hepatocellular carcinoma: tumor stiffening during compression induced by respiration to assess microvascular invasion.

[OBJECTIVES] Microvascular invasion is a strong prognostic factor in hepatocellular carcinomas. The aim of our study was to assess the diagnostic value of mechanical parameters measured with compression MR elastography to detect microvascular invasion in hepatocellular carcinomas.

[MATERIALS AND METHODS] In this prospective preoperative MR elastographic study, consecutive patients with hepatocellular carcinomas, scheduled for tumor surgical resection, were included. The tumor parameters assessed with MR elastography were the basal visco-elastic parameters (storage modulus, loss modulus, and phase angle, reflecting elasticity, viscosity and visco-elastic ratio) during expiration and inspiration, and the tumor stiffening slope during compression induced by respiration, reflecting non-linear elasticity. Microvascular invasion was determined with histopathological examination of resected tumors. Diagnostic performance of MR elastography was assessed with area under the receiver operating curve (AUC) analysis.

[RESULTS] The final study group consisted of 53 patients with complete surgical resection, MR elastography and histological data, including 31 patients with microvascular invasion. Compression stiffening slope and storage modulus difference between inspiration and expiration were significantly higher in hepatocellular carcinomas without than with microvascular invasion (p < 0.001 and p = 0.03, respectively). Among clinical, morphological and biomechanical imaging features, the MR elastography compression stiffening slope (p = 0.004) and histological WHO differentiation (p = 0.02-0.03) were the only independent determinants of hepatocellular carcinoma microvascular invasion. In contrast to basal biomechanical parameters, the compression stiffening slope had high diagnostic performance for detecting microvascular invasion (AUC = 0.83, p < 0.001).

[CONCLUSION] Our results suggest that the compression stiffening slope at MR elastography is useful to diagnose microvascular invasion in patients with hepatocellular carcinomas.

[KEY POINTS] Question Because non-invasive imaging markers of hepatocellular microvascular invasion are lacking, the development of new MRI markers is advisable. Findings In our MR elastography study, respiration-induced tumor stiffening, in contrast to basal visco-elastic parameters, had good accuracy for diagnosing hepatocellular carcinoma microvascular invasion. Clinical relevance Our results in patients with hepatocellular carcinomas suggest that the non-invasive measurement of MR elastography tumor compression stiffening slope may assess microvascular invasion.