What is the reason for the collapse of the area of the missing skull after craniotomy? Local collapse after cranial defect is very normal, as for the reason of collapse, it is very good to explain, because there is no local support of the skull, only a layer of scalp covers the outside of the brain, and the scalp is soft, there is no pressure-bearing role, then under the effect of the downward effect of gravity and atmospheric pressure, the localization of the cranial defect should naturally be collapsed, which is a normal phenomenon. If the cranial defect is not collapsed but inflated, then it is abnormal or even pathological, which may be due to the combination of other pathological factors, such as the presence of intracranial pressure increase phenomenon, the combination of intracranial hematoma, hydrocephalus, subdural hematoma, subcutaneous effusion, there is a penetrating deformity, or the combination of meningeal brain bulge, and so on. The general neurosurgical recommendation is that prompt cranial repair is needed about 3 months after the cranial defect. At this time, if the missing skull is collapsed or flat after craniotomy, this is normal and can be routinely performed cranial bone repair surgery; but if the cranial defect is not collapsed, but bulging, then the bulging needs to be dealt with first, and then cranial bone repair, which can be accomplished in one operation in most cases. So for some patients who ask the question what is the reason for the collapse of the missing cranial bone after craniotomy, don’t worry, this is normal; even if it is expanding outward, the surgeon can solve it properly and complete the cranial bone repair successfully.