Spontaneous re-ossification of a large calvarial defect in an older child.

LETTER to EDITOR The dura mater and the periosteum is considered to be a regulator of calvarial osteogenesis 1,2 and the phenomenon of calvarial reossification is well recognized in newborns and immature animals 1,3. The increased osteoinductive capacity of the immature dura is believed to be due to the increased expression of growth factors and extracellular matrix molecules 3 In older guinea pigs, small calvarial defects 3-5 mm in diameter were completely re-ossified spontaneously after 3 months, however defects more than 8 to 10 mm in diameter were not covered 4. The osteoinductive capacity of the dura to cover large craniectomy defects is generally lost in children above 2 years of age 5. Spontaneous re-ossification of large defects is possible, although rare in older children despite irradiation as demonstrated in this patient. A 12-year-old girl presented two years after midline posterior fossa craniectomy and radical excision of a vermian medulloblastoma followed by prophylactic craniospinal irradiation. In the present visit, she had features of raised intracranial pressure and Brain CT showed extensive metastasis of the tumour in bilateral basifrontal regions. In addition, a bridge of new bone formation was seen almost completely covering the earlier craniectomy defect. (Figure 1A, 1B) She was referred for further systemic therapy. The dura mater and the periosteum is considered to be a regulator of calvarial osteogenesis 1,2 and the phenomenon of calvarial reossification is well recognized in newborns and immature animals 1,3. The increased osteoinductive capacity of the immature dura is believed to be due to the increased expression of growth factors and extracellular matrix molecules 3. In older guinea pigs, small calvarial defects 3-5 mm in diameter were completely reossified spontaneously after 3 months, however defects more than 8 to 10 mm in diameter were not covered 4. The osteoinductive capacity of the dura to cover large craniectomy defects is generally lost in children above 2 years of age 5. Spontaneous re-ossification of large defects is possible, although rare in older children as demonstrated in this patient.