Decompressive craniectomy is a neurosurgical procedure that is used frequently for mass and/or intracranial hypertension. The Trephined Syndrome (or Sinking Skin Flap Syndrome) is a neurological deterioration which follows craniectomy and which is attributed to a large bone flap size. The symptomatology is varied but includes headache, aggravation of a hemisyndrome or cognitive disorders, often has an orthostatic component and improves or disappears with cranioplasty.