What is the general rule about kidney masses?

• A. They are malignant until proven benign.
• B. They are benign until proven malignant.
• C. Detection is based on size only.
• D. All masses are malignant until proven otherwise.

Answer: (D)

In evaluating a kidney mass, the default approach is to treat it as potentially malignant until proven benign. This cautious stance helps ensure cancer isn’t missed, since renal cell carcinoma can resemble benign lesions on initial imaging. While many masses may turn out benign, imaging alone often can’t definitively distinguish benign from malignant. So the workup emphasizes contrast-enhanced imaging to evaluate enhancement patterns and vascular characteristics, look for features like fat content that might suggest a benign angiomyolipoma, and, if needed, pursue tissue diagnosis or surgical removal to confirm pathology. Size by itself does not determine malignant potential, so management relies on imaging findings and, when necessary, biopsy or histology rather than size alone.