Tumors that grow in the active muscles of the body are called rhabdomyosarcoma. They occur in the head, neck, and pelvis, arms, or legs. The two most common types of Rhabdomyosarcoma are Embryonal Rhabdomyosarcoma. Found in children under 15, commonly in the head and neck region and genitourinary tract. Alveolar Rhabdomyosarcoma. A very aggressive, rare tumor that involves the muscles of the extremities or trunk. The most least common form of Rhabdomyosarcoma: Botryoid Rhabdomyosarcoma: A variant of the embryonal type arising as a grape-like lesion in mucosal-lined hollow organs such as the vagina and urinary bladder. Pleomorphic Rhabdomyosarcoma: Seen primarily in adults and arises in muscles of the extremities.