An 82-year-old woman in South America has just discovered she's carried a fetus for approximately 40 years.

Doctors in Colombia discovered the woman was carrying the unborn baby after she went to a Bogata hospital, suffering from abdominal pain.

X-rays revealed the calcified fetus, or lithopedion, inside her body.

Dr. Kemer Ramirez of Tunjuelito Hospital explained the attending physician noticed something "abnormal" in the woman's abdomen and immediately thought the anomaly was gallstones.

An ultrasound revealed nothing before a radiographer detected what appeared to be a tumor in the woman's abdominal cavity.

A lithopedion, otherwise known as stone child, is a dead fetus, usually the result of a primary or secondary abdominal pregnancy retained by the mother and then calcified over time.

Ramirez said the condition occurs when a fetus "does not develop in the uterus because it has moved to another place."

According to the Journal of the Royal Society of Medicine, the earliest known case of the phenomenon was discovered in 1582, during the autopsy of a 68-year-old woman in the French city of Sens. The woman had apparently carried her lithopedion for 28 years.

Doctors say a lithopedion may occur any time from 14 weeks gestation to full term. It actually is not unusual for a stone baby to remain undiagnosed for decades and not found until a patient is examined for some other reason.

Lithopedia can originate both as tubal or ovarian pregnancies.

In the latest Colombian case, the abdominal part of the woman was not viable for a pregnancy, "and this is what happened, a calcified fetus because the body is generating defense mechanisms and it is calcified until it stays there encapsulated," said Ramirez.

If the lithopedion becomes too large to be absorbed back into the body, it undergoes a process of mummification, with barriers of calcium protecting the mother from the decaying fetus. Then, the stone child can remain undiagnosed for years.

The woman in Bogota will undergo surgery to have the fetus -- mostly composed of dead tissue -- removed.

In 1880, German physician Friedrich Küchenmeister reviewed 47 lithopedia cases of from medical literature and identified three subgroups: Lithokelyphos, or "Stone Sheath," where calcification occurs on the placental membrane and not the fetus; Lithotecnon, or "Stone Son," where the fetus itself is calcified after having entered the abdominal cavity; and Lithokelyphopedion, or "Stone Sheath Child," where both fetus and sac are calcified.