When an 82-year-old Colombian woman presented to a hospital with stomach pains on Monday, doctors made a chilling discovery about what was causing her discomfort. She had been carrying a calcified fetus for the past 40 years.

According to a report in the Telegraph, doctors at Bogota’s Tunjuelito Hospital originally thought the woman was suffering from gastro-enteritis – a form of diarrhea. But when an ultrasound came back negative for the disease, doctors ordered an abdominal X-ray which ultimately located the fetus.

The woman’s condition is the result of a medical phenomenon known as lithopedion, in which a fetus develops – and dies – outside of the uterus in the abdominal cavity. If development stops and the fetus is too large to be absorbed into the body, it eventually calcifies outside the uterus to protect the mother from dead tissue.

Lithopedion is extremely rare, with fewer than 300 cases reported in medical literature.

After the discovery, the woman was transferred to another hospital, where she will undergo surgery to remove the fetus.

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