Renal cancer is a large socioeconomic problem, accounting for 3% of the estimated new cancer cases in men. During 2004 the American Cancer Society reported 35,710 new cases and estimated 12,480 deaths from renal cancer (Jemal et al. 2004). Historically renal cell carcinoma (RCC) has been detected by flank pain and hematuria. The widespread availability of cross-sectional imaging techniques such as ultrasound (US) and computed tomography (CT) led to an increased detection rate of small renal tumors (Pantuck et al. 2001). Further advances in medical imaging with the introduction of multidetector row spiral CT (MDCT) and magnetic resonance (MR) imaging in clinical routine have resulted in even earlier tumor detection. About two-thirds of all RCCs are now discovered incidentally (Homma et al. 1995). However, the differentiation of small renal tumors remains a diagnostic dilemma (Zagoria and Dyer 1998).