What do the terms gonadal and extragonadal mean?

"Gonadal" means "located in a gonad," which is a reproductive organ in males (testicle) or females (ovary). "Extra" attached to the front of any word means "outside of," so "extragonadal" means "outside of the testicles or ovaries." Gonadal extracranial (outside of the cranium, or skull) germ cell tumors grow in the testicles or ovaries; extragonadal extracranial germ cell tumors grow in areas of the body outside of the testicles or ovaries, most often the back of the abdomen (retroperitoneum) or the space between the lungs (mediastinum). Although the germ cells that make up the tumor originate in the gonads, they may move through blood vessels or lymph vessels (paths for your immune system) to these other parts of the body.