A former neighbor of mine had a hysterectomy, it's probably be 25 years ago or more.
It was done because she had a "tumor" in her uterus.
Turns out the "tumor" had hair, bits of what would be bone, teeth. The doctors determined that she probably had twins when she had her first child (who's about 35 now) and the one never completely formed, nor was it expelled when she delivered her daughter.
Stuff like this makes pregnancy ultrasounds, that are routinely done these days, a good thing.