The differences between patients and controls in each age group were not statistically significant (P> 0.05). The difference between the mean ICV for patients at a mean age of 5 months (887 mL) and at a mean age of 3 years (1369 mL) was 482 mL, an increase of 54.3%. The difference between the mean ICV for controls at a mean age of 5 months (854 mL) and at a mean age of 3 years (1358 mL) was 504 mL, an increase of 59%.
Patients with Apert syndrome (n = 3) had greater ICV than the rest of the group (n = 12) preoperatively (1067 mL vs 842 mL) and at 3 years follow-up (1538 vs 1318 mL). When patients with Apert syndrome were excluded, the results for the rest of the group were not significantly (P > 0.05) different from controls. Even when the 2 nonsyndromic cases were excluded, results were still not significantly different from controls.
In this study, we investigated the ICV in patients with BCS and compared it with an age- and gender-matched control group. We found that the ICV in patients was similar to that of normal children, both preoperatively and postoperatively, and that patients maintained their age-related ICV at follow-up. To date, there have been few published studies on ICV in patients with complex craniosynostosis, none specifically describing the ICV in BCS.
We measured the ICVs from CT scans by semiautomatic segmentation in a MATLAB-based program previously developed at our unit.11 Methods of ICV measurement have been improved over the last decades, from estimations using skull x-rays and mathematical formulas12,14 to the use of computerized software for measuring ICV from CT scans,11,13,15,16 or magnetic resonance imaging,17 or by indirect methods using three-dimensional (3D) photography.18 The disadvantages of using CT scans are the exposure to radiation and the need of anesthesia in some children, but ICV measurements from CT scans are more accurate than estimations from x-rays and 3D photographs. Magnetic resonance imaging has the advantage of accurately measuring brain and ventricular volumes separately. However, CT scans with low-radiation technique are currently used for diagnosis and follow-up at our unit. When using the 3D photography, there is no radiation; the ICV is estimated but can be converted into the absolute volume by dividing the estimated volume by a constant (1.34).18
Only a few studies have been published on normal ICV in children. The normative data of Lichtenberg14 from 1960 have previously been accepted and used by several authors.19–24 Posnick et al21 were surprised to find ICVs above the norms of Lichtenberg in a series of patients with metopic and sagittal craniosynostosis. The study by Posnick et al21 was later questioned by Marsh25 because of the selection of normative data. The norms presented by Lichtenberg were obtained from a French population using skull x-ray and mathematical formulas for ICV estimation. Abbott et al13 and Kamdar et al15 have presented normative data from CT scans. The problem is that almost all craniofacial centers use different methods of ICV measurement, and the accuracy might be questioned when comparing such data. When we compared the available normative data at the ages of 6 months, 12 months, and 36 months from Dekaban12 and Abbott et al13 with our own data (Table 2), our measurements were greater in these age groups compared with Dekaban’s, but more similar to Abbott’s study. The differences in ICV may be explained by differences in selection of control groups and in measurement methodologies.
In our previous study, Wikberg et al,11 the ICV measurements were evaluated for methodological errors. Precision was evaluated by running the program 10 times in each slice thickness, 0.6 mm and 5 mm. The differences between the 2 slice thicknesses were also calculated. In addition, human dry skulls were filled with agar gel and compared to the ICVs calculated from CT scans of the same skulls.
Surgical treatment of BCS has the purpose of increasing the ICV and normalizing the skull shape. Several surgical techniques are used at different craniofacial units. We use a combined procedure of frontal advancement and spring expansion of the posterior skull, together with biparietal restriction9 (Fig. 1). Vinchon et al26 use FOA with frontoparietal remodeling for nonsyndromic craniosynostosis with brachycephaly. Several craniofacial units use posterior skull expansion, with spring-assisted techniques27,28 or with distractors,8,29 as an initial surgical intervention in patients with BCS. Serlo et al29 propose posterior cranial expansion as an initial procedure for syndromic cases because of the greater gain in ICV compared to the previously used technique with frontal advancement. In our combined procedure, the increase in ICV for patients was comparable to the normal ICV growth in healthy children. We believe that the skull expansion will have positive effects for the patient by reducing the risk of raised ICP. The normalization of ICV and cranial shape will probably also be of importance when it comes to intellectual development and psychosocial abilities. The ICV is age dependent and for that reason we were not capable to compare our results with that of other centers due to the lack of published data in the age groups 6 months, 12 months, and 3 years. The heterogenecity and small numbers of this study may show a type II error in the statistical analysis, something one has to be aware of when interpreting the results. Further case-control studies will be required to determine whether our results are comparable to those of other centers.
We know very little about the natural history of patients with craniosynostosis, which is a substantial drawback in the interpretation of our results. Patients who have not been operated on may have normal, supranormal, or subnormal ICV, the latter with a risk of increased ICP, and a cranial deformity due to compensatory skull growth in uninvolved sutures. No patient in this study had a ventriculoperitoneal shunt. Another concern is the heterogenecity of our study, by including syndromic and nonsyndromic BCS, that may cause a different outcome.
The relationship between ICV and ICP is however not well defined in the literature. Gault et al24 presented a series of 66 children with craniosynostosis. Thirteen patients (20%) had raised ICP and 12 out of these (92%) also had a reduced ICV. Raised ICP was found to be more common in patients with multiple-suture craniosynostosis.24 Fok et al23 studied a series of 41 consecutive craniosynostosis cases; 38 patients (93%) had raised ICP, but only 4 (10%) had a reduced ICV.
Children with single-suture craniosynostosis may be more capable of compensating in their skull growth than patients with multiple-suture cranio-synostosis. Craniofacial anomalies with multiple-suture involvement are seen, for example, in Apert, Crouzon, Pfeiffer, and Saethre-Chotzen syndromes. These patients are more prone to develop intracranial hypertension,30,31 probably due to the lack of compensatory skull growth. Patients with Apert syndrome generally have a greater ICV compared with normal controls,19,20 and there is no discernible difference between the 2 genotypes Ser252Trp and Pro253Arg.32 Interestingly, Gosain et al20 noted that the ICV of patients with Apert syndrome was raised after 3.5 months of age, a raise that seemed unaffected by both ventriculomegaly and cranial vault surgery.
The skull surgery may not only keep the ICV in a normal range but also impair the skull growth, resulting in a reduced ICV. Therefore, to detect alterations, ICV measurements could be useful for surgical evaluation of patients with craniosynostosis.
In conclusion, patients with BCS who are operated on with the spring-assisted cranioplasty seem to maintain their age-related ICV at 3 years of age when compared with normal controls. Further studies will be required to determine whether these short-term results continue into adulthood.
We thank our medical photographers Åsa Bell and Niclas Löfgren. The study was performed in accordance with the Helsinki declaration on ethical principles for medical research. The study was approved by the Human Ethics Committee, the Medical Faculty at the University of Gothenburg (No. 784-11).
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© 2014 American Society of Plastic Surgeons
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