[A case of brain herniation due to delayed bone flap sinking].

Marked depression of the skin flap after external decompressive craniotomy, affecting the brain function, is known as sinking flap syndrome. However, to our knowledge, there have been no reports of delayed sinking of the entire bone flap after the procedure, inducing neurological symptoms. We encountered a patient with neurological symptoms due to sinking of the entire bone flap 15 years after the first operation. A 59-year-old male underwent clipping by craniotomy due to subarachnoid hemorrhage resulting from the rupture of a left internal carotid aneurysm 15 years earlier. He was discharged, but developed paresis in the right upper and lower limbs 6 months before symptom onset. CT showed sinking of the free bone flap, while MRI revealed left uncal herniation. After uncal resection and free flap fixation, the symptoms improved. This case confirmed the necessity of firm bone flap fixation at the time of cranial closure.