Renal hamartoma (also called angiomyolipoma) is a benign mix of fat, blood vessels, and muscle in the kidney. Most stay quiet, but if they grow or bleed they send clear signals. Painless flank ache is the early clue. It feels like a dull bruise below the ribs on one side and can throb after exercise or long sitting. Sudden severe pain means bleeding. The tumor’s fragile vessels burst, and the kidney swells fast—like a blow to the back that doesn’t fade. Blood may appear. Urine can turn light pink or contain small clots, often without any burning. A swollen lump... Learn more