Figure 1. In the mid-portion of the left kidney, there is a solitary enhancing mass that is slightly hypermetabolic (SUV_max 2.7).

Figure 2. There is no abnormal FDG uptake at the rectal surgical site. The hypermetabolic left renal lesion is seen. No other hypermetabolic lesions are present.

Incidental renal cell carcinoma.

Renal masses are known to be detected incidentally on FDG-PET/CT, as occurred in this patient. This modality however, is not as reliable in primary renal cell carcinoma (RCC) as in other cancers, primarily due to low sensitivity which occurs for two main reasons. Firstly, RCCs have variable glucometabolism, leading to variable FDG avidity, well demonstrated by the only mild hypermetabolic activity in this case. Secondly, false negative interpretation can also occur due to the presence of urinary activity adjacent to and obscuring the lesion; thus diuresis is important in the assessment of these lesions. Nevertheless, use of FDG-PET/CT has been shown to be useful in the assessment for metastases of renal cell carcinoma.