Renal cell carcinoma (RCC) is the most common type of kidney cancer, arising from the cells lining the renal tubules. It accounts for about 85 to 90 percent of malignant kidney tumors in adults. Many renal cell carcinomas are discovered incidentally during abdominal ultrasound performed for unrelated reasons. On sonography, RCC most commonly appears as a solid, heterogeneous mass that may be isoechoic, hypoechoic, or hyperechoic relative to the surrounding renal parenchyma. Larger tumors may contain areas of necrosis or calcification. Color Doppler often demonstrates internal vascularity. Extension of tumor into the renal vein or inferior vena cava can sometimes be identified. When a suspicious solid renal mass is found on ultrasound, CT or MRI is typically performed for further characterization and staging.