Intracranial volume in craniosynostotic rabbits

Quantitative analysis of cranial-orbital changes in infants with anterior synostotic plagiocephaly

PURPOSE

The effects of premature fusion of one coronal suture cause skull and orbital alterations in term of side-to-side asymmetry. This study aimed to quantify the cranio-orbital complex changes related to the severity of skull base dysmorphology in patients with unicoronal synostosis.

METHODS

Twenty-four infants affected by unicoronal synostosis were subdivided in three subgroups according to the severity of skull base deformity and their high-resolution CT images were quantitatively analyzed (groups IIa, IIb, III). Dimensions of cranial fossae, intracranial volume (ICV), ICV synostotic and ICV non synostotic side, whole brain volume (WBV), orbital volumes (OV), ICV/WBV, ICV_synostotic/ICV_{non-synostotic}, and OV_synostotic/OV_{non-synostotic} were evaluated.

RESULTS

Asymmetry and reduction in the growth of the anterior and middle fossae were found in all groups while asymmetry of the posterior cranial fossa was found only in IIb and III groups. In all groups, ICV, WBV, and ICV/WBV were not significantly different while ICV_synostotic/ICV_{non-synostotic} and OV_synostotic/OV_{non-synostotic} resulted significant difference (p < 0.05). ICV_{synostotic side} resulted reduction only in group III. OV on the synostotic side was not significantly reduced although a trend in progressively reducing volumes was noted according to the severity of the group.

CONCLUSION

Skull and orbital changes revealed a side-to-side asymmetry but the effects of the premature synostosis were more severe in group III suggesting an earlier timing of premature unicoronal synostosis in group III with respect to the other groups. The assessment of the skull base deformity might be an indirect parameter of severity of skull orbital changes and it might be useful for surgical planning.

Intracranial volume and whole brain volume in infants with unicoronal craniosynostosis

OBJECTIVE

Craniosynostosis has been hypothesized to result in alterations of the brain and cerebral blood flow due to reduced intracranial volume, potentially leading to cognitive deficits. In this study we test the hypothesis that intracranial volume and whole brain volume in infants with unilateral coronal synostosis differs from those in unaffected infants.

DESIGN

Our study sample consists of magnetic resonance images acquired from 7- to 72-week-old infants with right unilateral coronal synostosis prior to surgery (n  =  10) and age-matched unaffected infants (n  =  10). We used Analyze 9.0 software to collect three cranial volume measurements. We used nonparametric tests to determine whether the three measures differ between the two groups. Correlations were calculated between age and the three volume measures in each group to determine whether the growth trajectory of the measurements differ between children with right unicoronal synostosis and unaffected infants.

RESULTS

Our results show that the three volume measurements are not reduced in infants with right unicoronal synostosis relative to unaffected children. Correlation analyses between age and various volume measures show similar correlations in infants with right unicoronal synostosis compared with unaffected children.

CONCLUSIONS

Our results show that the relationship between brain size and intracranial size in infants with right unicoronal synostosis is similar to that in unaffected children, suggesting that reduced intracranial volume is not responsible for alterations of the brain in craniosynostosis.

Comparison of craniofacial phenotype in craniosynostotic rabbits treated with anti-Tgf-beta2 at suturectomy site

OBJECTIVE

Overexpression of transforming growth factor-beta 2 has been associated with craniosynostosis and resynostosis following surgery. We examined the effects of localized transforming growth factor-beta 2 inhibition on craniofacial phenotype in rabbits with craniosynostosis.

DESIGN

Twenty-five New Zealand white rabbits with bilateral coronal craniosynostosis were divided into three treatment groups: (1) suturectomy control (n=8); (2) suturectomy with nonspecific, control immunoglobulin G antibody (n=6); and (3) suturectomy with anti-transforming growth factor-beta 2 antibody (n=11). At 10 days of age, a coronal suturectomy was performed on all rabbits. The sites in groups 2 and 3 were immediately filled with a slow-resorbing collagen gel mixed with either immunoglobulin G or anti-transforming growth factor-beta 2 antibody. Computed tomography scans of each rabbit were acquired at ages 10, 25, and 84 days. Craniofacial landmarks were collected from three-dimensional computed tomography reconstructions, and growth and form were compared among the three groups.

RESULTS

Rabbits treated with anti-transforming growth factor-beta 2 antibody differed in form at 84 days of age compared with suturectomy control rabbits, specifically in the snout and posterior neurocranium. Growth in some areas of the skull was greater in rabbits from the anti-transforming growth factor-beta 2 group than in suturectomy control rabbits, but not significantly greater than in IgG control rabbits.

CONCLUSIONS

We find support for the hypothesis that transforming growth factor-beta 2 inhibition alters adult form, but these changes do not appear to be localized to the suturectomy region. Slight differences in form and growth between the two control groups suggest that the presence of the collagen vehicle itself may affect skull growth.

Noggin inhibits postoperative resynostosis in craniosynostotic rabbits

Inhibition of bone formation after surgery to correct craniosynostosis would alleviate the need for secondary surgeries and decrease morbidity and mortality. This study used a single dose of Noggin protein to prevent resynostosis and improve postoperative outcomes in a rabbit model of craniosynostosis.

INTRODUCTION

Craniosynostosis is defined as the premature fusion of one or more of the cranial sutures, which causes secondary deformations of the cranial vault, cranial base, and brain. Current surgical intervention involves extirpation of the fused suture to allow unrestricted brain growth. However, resynostosis of the extirpated regions often occurs. Several bone morphogenetic proteins (BMPs), well-described inducers of ossification, are involved in bone healing. This study tested the hypothesis that a postoperative treatment with Noggin, an extracellular BMP inhibitor, can inhibit resynostosis in a rabbit model of human familial nonsyndromic craniosynostosis.

MATERIALS AND METHODS

Thirty-one New Zealand white rabbits with bilateral coronal suture synostosis were divided into three groups: (1) suturectomy controls (n = 13); (2) suturectomy with BSA in a slow-resorbing collagen vehicle, (n = 8); and (3) suturectomy with Noggin in a slow-resorbing collagen vehicle (n = 10). At 10 days of age, a 3 x 15-mm coronal suturectomy was performed. The sites in groups 2 and 3 were immediately filled with BSA-loaded gel or Noggin-loaded gel, respectively. Serial 3D-CT scan reconstructions of the defects and standard radiographs were obtained at 10, 25, 42, and 84 days of age, and the sutures were harvested for histological analysis.

RESULTS

Radiographic analysis revealed that Noggin-treated animals had significantly greater coronal suture marker separation by 25 days and significantly greater craniofacial length at 84 days of age compared with controls. 3D-CT analysis revealed that Noggin treatment led to significantly greater defect areas through 84 days and to increased intracranial volumes at 84 days of age compared with other groups. Histological analysis supported CT data, showing that the untreated and BSA-treated groups had significant healing of the suturectomy site, whereas the Noggin-treated group had incomplete wound healing.

CONCLUSIONS

These data support our hypothesis that inhibition of BMP activity using Noggin may prevent postoperative resynostosis in this rabbit model. These findings also suggest that Noggin therapy may have potential clinical use to prevent postoperative resynostosis in infants with craniosynostosis.

Anti-TGF-??2 Antibody Therapy Inhibits Postoperative Resynostosis in Craniosynostotic Rabbits

BACKGROUND

Postoperative resynostosis is a common clinical finding. It has been suggested that an overexpression of transforming growth factor (TGF)-beta2 may be related to craniosynostosis and may contribute to postoperative resynostosis. Interference with TGF-beta2 function with the use of neutralizing antibodies may inhibit resynostosis. The present study was designed to test this hypothesis.

METHODS

New Zealand White rabbits with bilateral coronal suture synostosis were used as suturectomy controls (group 1, n = 9) or given suturectomy with nonspecific, control immunoglobulin G antibody (group 2, n = 9) or suturectomy with anti-TGF-beta2 antibody (group 3, n = 11). At 10 days of age, a 3 x 15-mm coronal suturectomy was performed. The sites in groups 2 and 3 were immediately filled with 0.1 cc of a slowly resorbing collagen gel mixed with either immunoglobulin G (100 mug per suture) or anti-TGF-beta2 (100 mug per suture). Three-dimensional computed tomography scan reconstructions of the defects were obtained at 10, 25, 42, and 84 days of age, and the sutures were harvested for histomorphometric analysis.

RESULTS

Computed tomography scan data revealed that the suturectomy sites treated with anti-TGF-beta2 showed significantly (p < 0.05) greater areas through 84 days of age compared with controls. Histomorphometry also showed that suturectomy sites treated with anti-TGF-beta2 had patent suturectomy sites and more fibrous tissue in the defects compared with sites in control rabbits and had significantly (p < 0.001) less new bone area (by approximately 215 percent) in the suturectomy site.

CONCLUSIONS

These data support the initial hypothesis that interference with TGF-beta2 function inhibited postoperative resynostosis in this rabbit model. They also suggest that this biologically based therapy may be a potential surgical adjunct to retard postoperative resynostosis in infants with craniosynostosis.

Postoperative Anti-Tgf-β2 Antibody Therapy Improves Intracranial Volume and Craniofacial Growth in Craniosynostotic Rabbits

Postoperative resynostosis and secondary craniofacial growth abnormalities are common sequelae after craniofacial surgery. It has been suggested that an overexpression of transforming growth factor-beta2 (Tgf-beta2) may be related to craniosynostosis and contribute to postoperative resynostosis. Interference with Tgf-beta2 function using neutralizing antibodies may inhibit resynostosis and improve postoperative craniofacial growth; the present study was designed to test this hypothesis. Twenty-nine New Zealand white rabbits with bilateral coronal suture synostosis were used: 1) suturectomy controls (n=9); 2) suturectomy with nonspecific, control IgG antibody (n=9); and 3) suturectomy with anti-Tgf-beta2 antibody (n=11). At 10 days of age, a 3 mm x 15-mm coronal suturectomy was performed. The sites in groups 2 and 3 were immediately filled with 0.1 cc of a slow resorbing collagen gel mixed with either IgG (100 microg/suture) or anti-Tgf-beta2 (100 microg/suture). Three-dimensional computed tomography scan reconstructions of the skulls and cephalographs were obtained at 10, 25, 42, and 84 days of age. Computed tomography scan data revealed patent suturectomy sites and significantly (P<0.05) greater intracranial volumes by 84 days of age in rabbits treated with anti-Tgf-beta2 compared with controls. Cephalometric analysis revealed significant (P<0.05) differences in craniofacial, cranial vault, and cranial base growth by 84 days of age in rabbits treated with anti-Tgf-beta2 compared with controls. These data support the initial hypothesis that interference with Tgf-beta2 function inhibited postoperative resynostosis and improved cranial vault growth in this rabbit model. Thus, this biologically based therapy may be a potential surgical adjunct in the treatment of infants with craniosynostosis.

Intracranial Volume Changes in Craniosynostotic Rabbits: Effects of Age and Surgical Correction

BACKGROUND

The premature fusion of one or more cranial sutures, termed craniosynostosis, alters normal brain growth patterns and results in compensatory changes in the cranial vault. The authors previously reported that bilateral coronal suture fusion resulted in a reduction in intracranial volume in a rabbit model of nonsyndromic, familial coronal suture synostosis.

METHODS

The current follow-up study involved collecting cross-sectional three-dimensional computed tomographic head scans from 142 rabbits (70 normal, 44 with uncorrected synostosis, and 28 synostosed rabbits with coronal suturectomy) at 0, 10, 25, 42, 84, and 126 days of age. Intracranial contents were reconstructed, and indirect intracranial volume was calculated.

RESULTS

Results revealed a significant (p < 0.05) postsynostotic reduction of intracranial volume (23 percent) by 25 days of age in rabbits with uncorrected craniosynostosis compared with normal controls, which continued through 84 days of age. Also, rabbits with surgically released synostosis, using a simple strip suturectomy, showed significantly (p < 0.05) greater intracranial volume at 25 days of age compared with unoperated synostosed rabbits. However, no changes in intracranial volume were noted between 42 and 84 days of age in rabbits with surgically released synostosis, at which point their intracranial volume was 30 percent less than that in normal control rabbits.

CONCLUSIONS

These data suggest that in rabbits with uncorrected craniosynostosis, compensatory changes in the neurocranium were not capable of compensating for the loss of sutures as growth sites. The results also showed that that surgical release of the synostosed suture improved intracranial volume in the short term (25 to 42 days) but failed to change it in the long term (42 to 84 days), possibly because of rapid resynostosis of the suturectomy site. This study suggests that surgical release of the suture fusion site alone may not be adequate to allow for normal intracranial volume growth in synostotic rabbits. For this reason, it may be efficacious to design and develop adjunct protein and gene therapies to prevent resynostosis and improve postoperative intracranial volume in craniosynostotic individuals.

Cytokine therapy for craniosynostosis

The birth prevalence of craniosynostosis (premature suture fusion) is 300-500 per 1,000,000 live births. Surgical management involves the release of the synostosed suture. In many cases, however, the suturectomy site rapidly reossifies, further restricts the growing brain and alters craniofacial growth. This resynostosis requires additional surgery, which increases patient morbidity and mortality. New findings in bone biology and molecular pathways involved with suture fusion, combined with novel tissue engineering techniques, may allow the design of targeted and complementary therapies to decrease complications inherent in high-risk surgical procedures. This paper selectively reviews recent advances in i) identifying genetic mutations and the aetiopathogenesis of a number of craniosynostotic conditions; ii) cranial suture biology and molecular biochemical pathways involved in suture fusion; and iii) the design, development and application of various vehicles and tissue engineered constructs to deliver cytokines and genes to cranial sutures. Such biologically based therapies may be used as surgical adjuncts to rescue fusing sutures or help manage postoperative resynostosis.

Transforming growth factor-beta isoform expression in the perisutural tissues of craniosynostotic rabbits

OBJECTIVE

To describe the expression patterns of the various transforming growth factor-beta (Tgf-beta) isoforms, known to be involved in suture development, in the perisutural tissues of rabbits with naturally occurring craniosynostosis and relate such differential expression to the pathogenesis of premature suture fusion.

METHOD

Twenty-one coronal sutures were harvested from six wild-type control New Zealand White rabbits and five rabbits with familial coronal suture synostosis at 25 days of age for histomorphometric and immunohistochemical analyses. Tgf-beta isoform immunoreactivity was assessed using indirect immunoperoxidase procedures with specific antibodies.

RESULTS

Synostosed sutures had significantly (p <.01) greater bone area and relatively more osteoblasts and osteocytes in the osteogenic fronts, compared with wild-type sutures. Tgf-beta isoform immunoreactivity showed differential staining patterns between wild-type and synostosed perisutural tissues. In wild-type sutures, Tgf-beta1 and Tgf-beta3 immunoreactivity was significantly (p <.001) greater than Tgf-beta2 staining in all perisutural tissues. In synostosed sutures, the opposite pattern was observed, with Tgf-beta2 immunoreactivity significantly (p <.001) greater than Tgf-beta1 and Tgf-beta3 in the osteogenic fronts, dura mater, and periosteum.

CONCLUSIONS

Findings from this study suggest that an overexpression of Tgf-beta2, either in isolation or in association with an underexpression of Tgf-beta1 and Tgf-beta3, may be related to premature suture fusion (craniosynostosis) in this pathological rabbit model. These abnormal expression patterns may be involved in premature suture fusion either through increased cell proliferation, decreased apoptosis of the osteoblasts or both at the osteogenic fronts.

Intracranial Pressure Changes in Craniosynostotic Rabbits

Cranial vault and brain deformities in individuals with craniosynostosis are thought to result, in part, from changes in intracranial pressure, but clinical findings are still inconclusive. The present study describes intracranial pressure changes in a rabbit model with naturally occurring, uncorrected coronal suture synostosis. Longitudinal and cross-sectional intracranial pressure data were collected from 241 New Zealand White rabbits, divided into four groups: normal controls (n = 81); rabbits with delayed-onset coronal suture synostosis (n = 78); rabbits with early-onset unilateral coronal suture synostosis (n = 32); and rabbits with early-onset bilateral coronal suture synostosis (n = 50). Epidural intracranial pressure measurements were obtained at 10, 25, 42, and 84 days of age using a NeuroMonitor microsensor transducer. Normal rabbits and rabbits with delayed-onset coronal suture and early-onset unilateral coronal suture synostosis showed a similar oscillating pattern of age-related changes in normal and head-down intracranial pressure from 10 to 84 days of age. In contrast, rabbits with early-onset bilateral coronal suture synostosis showed markedly elevated normal and head-down intracranial pressure levels from 10 to 25 days and showed a different pattern through 84 days. Results from one-way analysis of variance revealed significant (p < 0.01) group differences only at 25 days of age. Rabbits with early-onset bilateral coronal suture synostosis had significantly (p < 0.05) greater normal and head-down intracranial pressure (by 42 percent) than the other three groups. These results showed differing intracranial pressure compensations in rabbits with uncorrected multiple-suture synostosis compared with normal rabbits or rabbits with uncorrected single-suture synostosis, possibly through progressive cerebral atrophy and decreased intracranial volume, abnormal intracranial vascular patterns and blood volume, and/or differing cranial vault compensatory changes.

Rescue of coronal suture fusion using transforming growth factor-beta 3 (Tgf-beta 3) in rabbits with delayed-onset craniosynostosis

Craniosynostosis results in cranial deformities and increased intracranial pressure, which pose extensive and recurrent surgical management problems. Developmental studies in rodents have shown that low levels of transforming growth factor-beta 3 (Tgf-beta 3) are associated with normal fusion of the interfrontal (IF) suture, and that Tgf-beta 3 prevents IF suture fusion in a dose-dependent fashion. The present study was designed to test the hypothesis that Tgf-beta 3 can also prevent or "rescue" fusing sutures in a rabbit model with familial craniosynostosis. One hundred coronal sutures from 50 rabbits with delayed-onset, coronal suture synostosis were examined in the present study. The rabbits were divided into five groups of 10 rabbits each: 1) sham controls, 2) bovine serum albumin (BSA, 500 ng) low-dose protein controls, 3) low-dose Tgf-beta 3 (500 ng), 4) high-dose BSA (1,000 ng) controls, and 5) high-dose Tgf-beta 3 (1,000 ng). At 10 days of age, radiopaque amalgam markers were implanted in all of the rabbits on either side of the coronal suture to monitor sutural growth. At 25 days of age, the BSA or Tgf-beta 3 was combined with a slow-absorbing collagen vehicle and injected subperiosteally above the coronal suture. Radiographic results revealed that high-dose Tgf-beta 3 rabbits had significantly greater (P < 0.05) coronal suture marker separation than the other groups. Histomorphometric analysis revealed that high-dose Tgf-beta 3 rabbits also had patent coronal sutures and significantly (P < 0.01) greater sutural widths and areas than the other groups. The results suggest that there is a dose-dependent effect of TGF-beta 3 on suture morphology and area in these rabbits, and that the manipulation of such growth factors may have clinical applications in the treatment of craniosynostosis.

Early neuromotor behavior in craniosynostotic rabbits

OBJECTIVE

Clinical studies have shown both abnormal and normal mental and psychomotor development in patients with craniosynostosis. However, a number of confounding variables make study comparisons difficult. For these reasons, the present study describes early neuromotor development in an homogeneous rabbit model of craniosynostosis.

DESIGN

Fifty-three newborn New Zealand white rabbit kits were used: 13 were wild-type, normal control rabbits; 23 had delayed-onset coronal suture synostosis (onset is approximately 57 to 74 days post conception); and 17 had early-onset coronal suture synostosis (onset is approximately 21 to 25 days post conception). All rabbits were observed individually and blindly in an open field, daily for 2 minutes, from birth through the first 14 days of life. The first day of emergence of 10 different mature behaviors and developmental events (in developmental order of appearance: falling, righting, cliff avoidance, first sign of fur, body elevation, head elevation, circling, dragging, eye opening, and hopping) was recorded for each kit. Daily activity levels (grid crossing), and body weights were also recorded.

RESULTS

Significant group (p <.05) differences were observed in 9 of 11 measures. Both synostosed groups had significantly (p <.05) accelerated onset of behavior in 8 of 9 measures, compared with wild-type controls. The early-onset synostosis group had significantly (p <.05) accelerated onset in five of eight measures, compared with wild-type controls, and three of eight measures, compared with the delayed-onset synostosis group.

CONCLUSIONS

Synostotic rabbits showed precocious neuromotor development possibly through frontal lobe constrictions and altered brain activity from increased intracranial pressure, although primary genetic effects cannot be ruled out.

Cranial base changes following coronal suturectomy in craniosynostotic rabbits

It has been suggested that surgical release of synostosed sutures may ameliorate various cranial base abnormalities in craniosynostotic patients. The present study was designed to test this hypothesis in a rabbit model with familial coronal suture synostosis (CSS). Data were collected from 56 New Zealand White rabbits: 32 unaffected controls, 11 with unoperated CSS, and 13 with CSS released by suturectomy performed at 25 days of age. Serial radiographs were taken at 25, 42 and 84 days. Linear, angular and triangular shape cranial base measurements were compared using ANOVA and tensor biometric analysis. Results revealed that at 84 days, both groups of CSS rabbits had significantly (p < 0.05) different anterior and total cranial base lengths, flatter cranial base angles, and dysmorphic anterior cranial base shapes when compared with normals. Significant (p < 0.05) differences were noted only for palatal and cranial base angles and posterior cranial base shape between CSS rabbits with and without suturectomy. However, significant (p < 0.05) changes were noted between pre- and postoperative measurements in posterior and total cranial base lengths and anterior and posterior cranial base shapes in CSS rabbits with suturectomy. Results revealed that surgical release of synostosed coronal sutures through suturectomy did not normalize cranial base growth patterns in CSS rabbits. These findings may be explained by the relatively late age of surgical release or suturectomy site resynostosis with continued dysmorphic cranial base growth. Alternatively, cranial base abnormalities seen in CSS rabbits may be early primary malformations, not secondary deformations amenable to surgical modification.

Endocranial vascular patterns in a familial rabbit model of coronal suture synostosis

OBJECTIVE

The present study investigates the potential relationship between craniosynostosis and any changes in endocranial vasculature. The hypothesis that crania from rabbits with familial, nonsyndromic coronal suture synostosis and crania from rabbits with experimental immobilization of the coronal suture are associated with altered form of the middle meningeal vessels and dural venous sinuses is tested.

DESIGN

Silicone rubber endocasts from 14 adult New Zealand white rabbits (Oryctolagus cuniculus) with familial nonsyndromic coronal suture synostosis (five with bilateral coronal suture synostosis and nine with unilateral coronal suture synostosis) were made to assess middle meningeal vessel and dural venous sinus form. For comparative purposes, endocasts were made from 25 rabbits with normal, patent coronal sutures and 10 rabbits with experimental immobilization of the coronal suture. Impressions of the dural venous sinuses were assessed for depth and width. The area of the confluens of sinuses was also assessed. Impressions of the middle meningeal vessels were assessed for depth, width, and degree of convolution. For width of the dural venous sinuses and area of the confluens of sinuses, comparisons among groups were made with a one-way analysis of variance (ANOVA). For depth of the dural venous sinuses and impressions of the middle meningeal vessels, comparisons among groups were made using a Kruskal-Wallis one-way ANOVA.

RESULTS

Crania with familial coronal suture synostosis had significantly (p <.05) reduced posterior dural venous sinus dimensions when compared with both crania from rabbits with experimental immobilization of the coronal suture and rabbits with normal coronal sutures. Crania with both coronal suture synostosis and experimental immobilization had significant increases in dimensions of the middle meningeal vessels relative to normal crania. In addition, casts from rabbits with unicoronal suture synostosis showed marked asymmetry in the dural venous sinuses.

CONCLUSIONS

These results support the hypothesis that craniosynostosis is associated with alterations in endocranial vasculature. These changes are most likely a secondary response to synostosis rather than a causal factor and may reflect increased intracranial pressure, decreased intracranial volume, and local accumulations and reductions of cerebrospinal fluid in the posterior region of the skull and immediately deep to the coronal suture.

Trigonocephaly in rabbits with familial interfrontal suture synostosis: the multiple effects of premature single-suture fusion

Previous studies from our laboratory have characterized the craniofacial morphology and growth patterns of an inbred strain of rabbits with autosomal dominant coronal suture synostosis. A number of rabbit perinates from this colony have been collected sporadically over a 5-year period with premature interfrontal suture synostosis. The present study describes the very early onset of craniofacial dysmorphology of these rabbits and compares them to similar-aged normal control rabbits. A total of 40 perinatal New Zealand White rabbits were used in the present study. Twenty-one comprised the sample with interfrontal suture synostosis and ranged in age from 27 to 38 days postconception (term = 31 days) with a mean age of 33.53 days (+/-2.84 days). Nineteen rabbits served as age-matched, normal controls (mean age = 33.05 days +/-2.79 days). Lateral and dorsoventral radiographs were collected from each rabbit. The radiographs were traced, computer digitized, and 12 craniofacial measurements, angles, and indices were obtained. Mean measures were compared using an unpaired Student's t-test. All synostosed rabbits were stillborn or died shortly after birth. Grossly, these rabbits exhibited extreme frontal bossing, trigonocephaly with sagittal keeling, and midfacial shortening. No somatic anomalies were noted. Radiographically, rabbits with interfrontal suture synostosis had significantly (P < 0.05) narrower bifrontal widths, shorter cranial vault lengths, kyphotic cranial base angles, and different cranial vault indices (shapes) compared to controls. Results reveal severe and early pathological and compensatory cranial vault changes associated with premature interfrontal suture synostosis in this rabbit model. The 100% mortality rate noted in this condition may be related to the inheritance of a lethal genetic mutation or to neural compression from reduced intracranial volume. Results are discussed in light of current pathogenic hypotheses for human infants with premature metopic suture synostosis.

Age-related changes in intracranial pressure in rabbits with uncorrected familial coronal suture synostosis

OBJECTIVE

Chronic, elevated intracranial pressure (ICP) in craniosynostotic infants may result in ocular and neurocapsular problems; however, not all infants exhibit elevated ICP. Clinical ICP studies are further confounded by small and heterogeneic samples, multiple-suture involvement, and varying surgical management protocols. The present study was designed to describe longitudinal changes in ICP in a large, homogenous sample of rabbits with uncorrected familial, nonsyndromic coronal suture synostosis.

METHODS

Ninety-one rabbits were divided into four groups: (1) normal rabbits (n = 28), (2) rabbits with delayed-onset coronal suture synostosis (DOCS; n = 25), (3) rabbits with unilateral coronal suture synostosis (UCS; n = 12), and (4) rabbits with bilateral coronal suture synostosis (BCS; n = 26). ICP was measured at 24 and 42 days of age using a Codman epidural microtransducer.

RESULTS

Rabbits with BCS had a significantly (p < .05) higher mean ICP at 25 days of age than rabbits in the other three groups by approximately 146%. However, by 42 days of age, mean ICP in normal control rabbits and rabbits with DOCS was significantly (p < .01) increased compared with their mean ICP values seen at 25 days of age, while mean ICP in BCS rabbits significantly (p < .01) decreased (by 32%) over the same time period. ICP in rabbits with UCS was between that seen in normal control rabbits and rabbits with BCS and did not significantly (p > .05) change over time.

CONCLUSIONS

These findings suggest that the degree of suture involvement may be related to early increases in ICP. Possible multifactorial explanations for intracranial decompression and compensation in the craniosynostotic rabbit model are discussed.

Brain growth rates in craniosynostotic rabbits

OBJECTIVE

It has been suggested that abnormal brain morphology or growth rates may be a primary causal factor of craniosynostosis due, in part, to a lack of normal growth stretch and tension at the sutural margins. The purpose of the present study was to quantify cerebral hemisphere morphology and growth in a rabbit model of nonsyndromic coronal suture synostosis to determine whether cerebral dysmorphology is primary or secondary to synostosis in this model.

DESIGN

Fifty-seven brains (114 hemispheres) were examined from 40 normal control rabbits and 17 rabbits with bilateral coronal suture synostosis ranging in age from 25 to 450 days postconception (synostosis occurs at approximately 23 days postconception in this model). The calvariae were removed, the brains were fixed in 10% paraformaldehyde, and in situ bilateral measurements of cerebral hemisphere length and cerebral hemisphere width were obtained using a Wild microscope with a camera lucida attachment and digital caliper. Regression analysis was used to compare cerebral cortex growth rates by age between the two groups.

RESULTS

Cerebral hemisphere width and cerebral index regression line slopes had similar y intercepts (23 day postconception) with significantly (p < .05) diverging slopes over time. Normal rabbits increased more rapidly than synostosed rabbits. No significant (p > .05) differences were noted in regression line slopes between groups for cerebral hemisphere length by age or length by width.

CONCLUSIONS

Cerebral dysmorphologies are probably a compensatory, secondary (postsynostotic) event and not a primary causal factor of craniosynostosis in this rabbit model of human familial, nonsyndromic coronal suture synostosis.