A comparison of single-stage versus gradual fronto-parietal advancement in terms of extradural dead space and bone deposition

Summary This study was designed to investigate the differences between single-stage and gradual advancement of cranial vault in adult cats. Fifteen animals underwent fronto-parietal craniotomy including the roof of the frontal sinus. They were randomly assigned to three experimental groups; single-stage advancement ( n = 5), gradual distraction with intact dura-bone attachments ( n = 5), and gradual distraction after separation of the dura from the fronto-parietal bone segment ( n = 5). Development of an extradural dead space and new bone formation were evaluated with CT scans at 1, 4 and 12 weeks. After sacrificing the animals at 12 weeks, midsagittal frozen sections and decalcified coronal sections of the heads were obtained. The single-stage advancement group developed an extradural dead space which communicated with the frontal sinus. The advanced bone segment, which was exposed to the air-filled dead space, showed bony resorption. Both groups of gradual advancement showed enlargement of the cranial cavity and frontal sinus. As the dura and brain were stretched superiorly, no extradural dead space was produced. Although the distraction gap demonstrated deposition of new bone in both gradual advancement groups, the bone formation was less pronounced in distraction after separating the dura from the bone segment. In conclusion, gradual distraction of a fronto-parietal bone prevents extradural dead space formation regardless of whether the dura is kept attached to or it is separated from the distracted bone segment. Devascularization of the bone segment by dissecting off the dura, however, decreases new bone formation, and thus may increase a risk of relapse.