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

Abstract

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.

Keywords: Computed tomography; Magnetic resonance imaging; Mixed epithelial and stromal tumor of the kidney; Radiologic features; Renal mass.

Fig. 1

Imaging findings in a 47-year-old female with mixed epithelial and stromal tumor of the kidney. (A–C) Axial-unenhanced (A), arterial phase contrast-enhanced (B), and nephrographic phase contrast-enhanced (C) computed tomography (CT) scans demonstrate a well-marginated mass in the left kidney containing cystic lesions and a solid component (arrow). The solid component shows high attenuation on nonenhanced CT and is slightly enhanced on dynamic CT. (D, E) Axial (D) and coronal (E) T2-weighted magnetic resonance images showing T2-hypointensity of the solid component.

Fig. 2

Histological findings of MEST case 1. (A) Hematoxylin-Eosin stain. The solid component of the tumor consisted of stromal spindle cells. (B–D) Immunohistochemical study. Stromal spindle cells were positive for progesterone, estrogen receptors (B), smooth muscle actin, and desmin (C). Stromal components were negative for HMB-45 (D).

Fig. 3

Imaging findings in a 28-year-old female with mixed epithelial and stromal tumor of the kidney. (A–C) Axial-unenhanced (A), arterial phase contrast-enhanced (B), and nephrographic phase contrast-enhanced (C) computed tomography (CT) scans show a well-demarcated, heterogeneous, exophytic mass with cysts in the right kidney. The solid part consists of 2 different components; one is hyperattenuating and gradually enhances (arrow), and the other is isoattenuating with only slight enhancement on dynamic CT. (D, E) In-phase (D) and out-of-phase (E) magnetic resonance (MR) images show minimal solid fat in the solid component (arrowhead). (F) Axial T2-weighted MR image. The solid component without fat has 2 different parts; one is T2-hypointense and the other is T2-hyperintense. The T2-hypointense solid part appears to be compatible with the hyperattenuating lesion on unenhanced CT.