Radiologic features of mixed epithelial and stromal tumors of the kidney: Hyperattenuating on unenhanced computed tomography and T2-hypointensity on magnetic resonance imaging.

In the 2016 World Health Organization renal tumor classification, the mixed epithelial and stromal tumor family was introduced as a new entity. This family encompasses a spectrum of tumors, ranging from predominantly cystic tumors (adult cystic nephromas) to tumors that are variably solid (mixed epithelial and stromal tumors). The majority of previous studies incorporating "mixed epithelial and stromal tumor" in the titles were actually reports of imaging findings of adult cystic nephroma. Thus, the solid component of mixed epithelial and stromal tumors has not been well evaluated. In this study, we present 2 cases of mixed epithelial and stromal tumors, as defined by the 2016 World Health Organization classification, showing a predominantly solid component. The characteristic findings of the solid component of these tumors were T2-hypointensity on magnetic resonance imaging and hyperattenuation on unenhanced computed tomography. Angiomyolipoma with epithelial cysts and epithelioid angiomyolipoma should be considered in the differential diagnosis of mixed epithelial and stromal tumors.