Metopic and sagittal synostosis: intracranial volume measurements prior to and after cranio-orbital reshaping in childhood.

This study applied a proven method for obtaining intracranial volume measurements using CT scans to (1) measure the intracranial volume of a consecutive series of children with either metopic or sagittal synostosis prior to any craniofacial procedure, (2) perform a standard cranio-orbital operation in each child, follow them longitudinally, and remeasure their intracranial volume 1 year later, and (3) compare their intracranial volumes with those of an age- and gender-matched cohort and review their cranial growth velocity. The study included 18 children who presented sequentially with untreated isolated nonsyndromic sagittal (n = 8) and metopic (n = 10) synostosis between 1987 and 1990 and who subsequently underwent cranio-orbital reconstruction by the senior author (Posnick) in conjunction with a pediatric neurosurgeon. The primary method of osteotomy and bone-graft fixation varied (i.e., wires, miniplates and microplates and screws). The series included 5 females and 13 males with an average age at the time of operation of 27 months (range 6 to 87 months). The postoperative clinical follow-up ranged from 13 to 47 months at the close of the study. Comparison of our patients' preoperative intracranial volumes with age- and gender-matched volumes available through Lichtenberg showed that 16 of 18 (89 percent) had volumes at or greater than the mean, with 44 percent (7 of 16) exceeding 2 standard deviations above the mean. When comparing our patients' late postoperative volumes with the Lichtenberg normative measurements, 94 percent achieved values at or greater than the mean. All patients achieved increased intracranial volume in association with the surgery performed and the time that lapsed between scan intervals. The majority of our patients (16 of 18) followed an intracranial volume growth curve that closely approximated the norm but with a starting point determined by the preoperative value. Two of 18 followed a growth curve that exceeded the rate of expansion expected for normal children. Our findings suggest that premature closure of either the sagittal or metopic suture does not result in diminished intracranial volume prior to or after the cranio-orbital procedures carried out in childhood. For the majority of the children in our study, both the preoperative intracranial volume and the rate of cranial expansion approximated or surpassed that of children without synostosis. The surgical techniques of skull and upper orbital reshaping with varied forms of osteotomy and graft fixation did not result in a global form of growth restriction. These findings are contrary to standard thinking about the biologic effects of craniosynostosis and raise new questions about our rationale for treatment.