Purpose To evaluate the MRI findings of renal cell carcinoma (RCC), including findings on diffusion-weighted images (DWIs) and chemical shift images (CSIs), in patients with acquired cystic disease of the kidney (ACDK) in relation to the histopathologic findings. Materials and Methods Two radiologists retrospectively reviewed the MRI findings of 10 RCCs in seven consecutive patients with ACDK. They evaluated the signal intensities (SIs) and signal homogeneity of the lesions on T2-weighted images, DWIs, and T1-weighted images. Thereafter, they evaluated the cytoplasmic fat in the lesions by CSIs. After image analyses, the MRI findings were correlated with the histopathologic findings. Results The RCCs tended to show heterogeneous high SIs on T2-weighted images and DWIs. The high SIs on DWIs were mainly attributable to the viable parts, and the heterogeneity was due to the various SIs arising from the intratumoral degenerative components. Unlike the reported findings for hemorrhagic cysts, the RCCs did not show homogeneous high SIs or fluid-iron levels on T1-weighted images. The four lesions, in which the presence of cytoplasmic fat was suggested on CSIs, were clear cell RCCs. Conclusion The MRI findings, including findings on DWIs and CSIs, well reflected the histopathologic findings of RCC in patients with ACDK.
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