A kidney cyst is a fluid-filled bubble on or in the kidney. Most stay small and silent, but when they grow or bleed they start whispering warnings. Flank ache is the usual first talker. It feels like a dull bruise just below the ribs or a sudden cramp if the cyst stretches fast. Urinary changes can tag along. You may notice more trips, a weaker stream, or the sense the bladder never fully empties. Blood in the urine sometimes shows. The color may be light pink or tea-brown, often painless and spotted only in the first morning pee. A swollen... Learn more