Elephantiasis. Coloured X-ray showing the lower leg of a patient with elephantiasis, a condition where the lymph vessels (pink) become blocked. The vessels are visible due to the injection of a substance that absorbs X-rays. Lymph vessels carry fluid to allow the exchange of water, salts, proteins and other substances between the blood and tissues. Blockage causes fluid build-up (oedema), leading to severe swelling. The most common cause of elephantiasis is infection with parasitic worms (filariasis), which can affect the limbs, breasts, scrotum or vulva. The bones of the lower leg and foot are also seen (pale green).