Craniocerebral disproportion after decompressive craniectomy in infants: The hidden enemy of cranial repair?

Introduction Cranioplasty aims at restoring the physiological integrity and volume of the skull. Any disproportion between the intracranial content and the volume of the container may favor the occurrence of complications. A classification of volume mismatches is proposed. A negative mismatch, consisting of intracranial content minor to skull volume, is well represented by the sinking flap. On the other side, a positive mismatch, consisting of intracranial content higher than skull volume, usually depends on CSF collection or hydrocephalus once the brain edema is regressed. Though, in children, this condition may result from physiological brain growth after decompressive craniectomy. Treatment algorithm based on this classification is presented. Illustrative case A 1-year-old boy with a severe traumatic brain injury underwent right decompressive craniectomy, evacuation of subdural hematoma, and dural expansion at another institution. After failure of autologous bone-assisted cranioplasty for infection, a helmet was recommended in order to postpone the cranial repair. Patient was admitted to our institution 3 years later. CT scan showed brain herniation through the cranial defect, associated to a condition of acquired craniocerebral disproportion, due to the condition of "open skull". Augmented hydroxyapatite cranioplasty (CustomBone, Finceramica, Faenza, Italy) was performed in order to manage this rare condition of positive volume mismatch. Subsequent course was uneventful and no complication was recorded at 30-month follow-up. Conclusions This illustrative case highlights the possible occurrence of a positive structural mismatch between the skull and the intracranial content after decompressive craniectomy, thus configuring a condition of acquired craniocerebral disproportion, aside of other brain or CSF complications. We firstly recognize this condition in the literature and propose it as a possible factor affecting the outcome of cranioplasty in infants and young children.