A rare condition in which the blood is not able to clot and serious bleeding may occur. It occurs in some patients who have blood vessel tumors called tufted angiomas and kaposiform hemangioendotheliomas. These tumors usually form on the skin but may also form in deeper tissues, such as muscle and bone. The tumors may grow quickly and trap and destroy platelets, which are needed to form clots and stop bleeding. Kasabach-Merritt syndrome is most common in infants and young children.