Fat-rich AML is defined as a lesion mea- suring –10 HU or less on unenhanced CT images .This subtype constitutes approximately 95% of renal AMLs. Almost all fat-rich AMLs are easily diagnosed with unenhanced CT alone because fat, a hallmark of AML, is clearly visualized.”
Renal Angiomyolipoma Based on New Classification: How to Differentiate It From Renal Cell Carcinoma 
Byung Kwan Park 
AJR 2019; 212:582–588

“Approximately 5% of renal AMLs histo- logically have a small amount of fat and correspond to fat-poor AML or fat-invisible AML in the Song classification. Among small (< 4 cm) renal tumors, 4–13% are histologically confirmed as AML because imaging shows too little fat. Many authors have shown that AML with a small amount of fat is likely to have female predominance, small size, and a more homogeneous texture than RCC”
Renal Angiomyolipoma Based on New Classification: How to Differentiate It From Renal Cell Carcinoma 
Byung Kwan Park 
AJR 2019; 212:582–588

Average HU of -63

“ In the corticomedullary phase, attenuation values of renal clear cell carcinoma were significantly higher than those of renal papillary carcinoma. In renal clear cell carcinoma the mean attenuation value was 152.6 HU (range 90-256 HU); in renal papillary carcinoma, the value was 61.8 HU (range 38-123 HU).”
Differentiation of Renal Clear Cell Carcinoma and Renal Papillary Carcinoma Using Quantitative CT Enhancement Parameters
Ruppert-Kohlmayr
AJ et al.AJR 2004; 183:1387-1391

“ In the corticomedullary phase, attenuation values of renal clear cell carcinoma were significantly higher than those of renal papillary carcinoma. The accuracy was 95.7%; the sensitivity 98.3% and the specificity, 92% when using 100HU as the cutoff value.”
Differentiation of Renal Clear Cell Carcinoma and Renal Papillary Carcinoma Using Quantitative CT Enhancement ParametersRuppert-Kohlmayr
AJ et al.
AJR 2004; 183:1387-1391

“ Ninety percent of clear cell renal cell carcinomas (RCCs) are hypervascular and demonstrate a heterogeneous enhancing pattern of mixed enhancing solid soft tissue components and low attenuation necrotic or cystic areas.”
Solid Renal Cortical Tumors: Differentiation with CT
Zhang J et al.
Radiology 2007; 244:494-504

“ Imaging features at multiphasic multidetector CT correlate with cytogenetic characteristics of ccRCCs, which may affect patient prognosis and possibly help predict response to molecular targeted therapies.”
Clear Cell Renal Cell Carcinoma: Multiphasic Multidetector CT Imaging Features Help Predict Genetic Karyotypes
Sauk SC et al.
Radiology 2011; 261:854-862

“The natural history of ccRCC is variable, with some tumors exhibiting an indolent growth pattern and others demonstrating aggressive behavior including local recurrence after resection and distant metastases. Histologically defined tumor necrosis in ccRCC has been shown to be an independent negative prognostic factor for metastasis and overall survival. In fact, histologically defined tumor necrosis is integrated into prognostic scoring systems such as the stage, size, grade, and necrosis score.”
Nonenhancing Component of Clear Cell Renal Cell Carcinoma on Computed Tomography Correlates With Tumor Necrosis and Stage and Serves as a Size-Independent Prognostic Biomarker 
Ahmed FS et al.
J Comput Assist Tomogr 2019;43: 628–633

Objectives: This study aimed to quantify nonenhancing tumor (NT) component in clear cell renal cell carcinoma (ccRCC) and assess its association with histologically defined tumor necrosis, stage, and survival outcomes. Results: Nonenhancing tumor was higher in ccRCC with tumor necrosis (11% vs 7%; P = 0.040) and higher pathological stage (P = 0.042 and P < 0.001, respectively). Patients with greater NT had higher incidence of cancer recurrence after resection (P < 0.001) and cancer-specific mortality (P < 0.001). Conclusion: Nonenhancing tumor on preoperative computed tomographic scans in patients with ccRCC correlates with tumor necrosis and stage and may serve as an independent imaging prognostic biomarker for cancer recurrence and cancer-specific survival. 
Nonenhancing Component of Clear Cell Renal Cell Carcinoma on Computed Tomography Correlates With Tumor Necrosis and Stage and Serves as a Size-Independent Prognostic Biomarker 
Ahmed FS et al.
J Comput Assist Tomogr 2019;43: 628–633