A French man whose skull was mostly occupied by a "huge fluid-filled chamber" was able to operate perfectly well as a civil servant - despite having "little more than a thin sheet of actual brain tissue", Reuters reports.
The 44-year-old's condition was revealed when he went to hospital suffering from mild weakness in his left leg. A probe of his medical history revealed he'd had a shunt inserted into his skull as an infant to relieve hydrocephalus, which was removed when he was 14.
Doctors were "amazed" when computed tomography and magnetic resonance imaging scans showed "massive enlargement" of his lateral ventricles, "usually tiny chambers that hold the cerebrospinal fluid that cushions the brain".
Dr Lionel Feuillet and colleagues at the Universite de la Mediterranee in Marseille explained in a letter to The Lancet: "He was a married father of two children, and worked as a civil servant." Tests revealed the chap's IQ as 75, below average but evidently no impediment to leading a normal life.
Dr Max Muenke, a paediatric brain defect specialist at the National Human Genome Research Institute, said: "What I find amazing to this day is how the brain can deal with something which you think should not be compatible with life. If something happens very slowly over quite some time, maybe over decades, the different parts of the brain take up functions that would normally be done by the part that is pushed to the side." ®