Lithopedion

Incidentally-discovered calcified pelvic mass during workup for low back pain in a 56-year old woman. The patient recalled abnormal obstetric history 30 years ago. Otherwise, there was no relevant clinical or lab abnormality. CT scan clearly shows an extra-uterine calcified fetal skeleton on MPCR (multi-planar curved reformat) images.
A lithopedion (litho = stone; pedion = child), or stone baby, is a rare phenomenon which occurs most commonly when a fetus dies during an ectopic pregnancy. If the dead fetus is too large to be re-absorbed by the mother’s body it becomes a foreign body to the mother’s immune system. To protect itself from possible infection, the mother’s body will encase the fetus in a calciferous substance. The fetus is gradually mummified becoming a stone baby. Lithopedions
may occur from 14 weeks’ gestation to full term. It is not unusual for a stone baby to remain undiagnosed for decades and found incidentally when taking plain films for various reasons (like this case).
References:
1. Wikipedia
2. Chang, et al. Lithopedion case report Chinese Medical Journal (Taipei) 2001;64:369-372
Credit: Dr Ahmed Haroun
http://www.radpod.org