Hi, Thanks for writing in. You might have a lipoma or angiomyolipoma in your kidney. These are harmless fat containing benign tumors in the kidney. Lipoma is a pure fat containing tumor. Lipoma tumours of the kidney start in the cells of the fat that surrounds the kidney. They are more common in middle-aged women. Lipoma tumours can grow to be quite large. Angiomyolipoma is a benign kidney tumour made up of fat, blood vessels and smooth muscle tissue. Even though it’s benign, the tumour can spread into and destroy surrounding tissue. It can also cause sudden bleeding (hemorrhage) from the kidney into the abdomen. Bleeding is more likely with tumours that are larger than 4 cm (1-1/2 inches). It is important to know which tumor you have and the size. Surgery is required only if there is pain, bleeding and blood in urine.