Renal epithelioid angiomyolipoma: Incidence in a Japanese cohort and diagnostic utility of diffusion‐weighted magnetic resonance imaging

Abstract

Objectives To show the epidemiological characteristics of epithelioid angiomyolipoma in a Japanese population, and to establish the preoperative diagnosis method of epithelioid angiomyolipoma. Methods Among the 855 tumors of patients who underwent partial/radical nephrectomy or renal biopsy for presumed renal cell carcinoma between 2007 and 2018, 39 renal tumors were diagnosed as nonclassical angiomyolipoma, including epithelioid angiomyolipoma and fat‐poor angiomyolipoma. We retrospectively evaluated the incidence of epithelioid angiomyolipoma. Furthermore, we analyzed computed tomography and magnetic resonance imaging results, including diffusion‐weighted magnetic resonance imaging findings of epithelioid angiomyolipoma and fat‐poor angiomyolipoma. Results The incidence of epithelioid angiomyolipoma (n = 7) was 17.9% of surgically resected non‐classical angiomyolipoma. The radiological appearance of epithelioid angiomyolipoma was hyperattenuating on unenhanced computed tomography images with iso or low intensity on T2‐weighted magnetic resonance imaging. The mean apparent diffusion coefficient value of the solid component in epithelioid angiomyolipoma was significantly lower than that in fat‐poor angiomyolipoma (median 0.79 × 10⁻³ vs 1.07 × 10⁻³ mm²/s, P = 0.0019). Conclusions The proportion of epithelioid angiomyolipoma in our Japanese cohort was equivalent to that of the reported series in the USA. The apparent diffusion coefficient value is potentially useful to differentiate between epithelioid angiomyolipoma and fat‐poor angiomyolipoma. Further research is required to establish the imaging diagnostic criteria for epithelioid angiomyolipoma.