Thirteen-year-old Florian Barreiros had visited to the CHU hospital in Amiens for a run-of-the-mill MRI scan on his pancreas, but was left needing a thumb transplant too.
Due to what is understood to be a hospital error, medics left a monitory sensor on his hand which burned his thumb "through to the bone".
As Florian was under anesthetic at the time of the scan in order to keep his body still, he didn't notice the burning until it was too late.
"My child was screaming with pain. He has suffered a real torture here," the boy's mother told the Courrier Picard newspaper.
She said that none of the medical staff informed her of the accident either, and that she found her son, who has Down's Syndrome, screaming in the emergency room several hours after the scan.
The mother raised the matter with a local prosecutor on Wednesday, after she claims to have been threatened by medical staff when she said she would share the story with the press.
Magnetic resonance burns during MRIs occur when a closed-loop conduction system is created due to the patient's skin coming in contact with a wire or metal.