A commentary on the growth of the human brain and skull

A Geometric Morphometric Study on Sexual Dimorphism in Viscerocranium

The level of sexual dimorphism manifested by human bones is an important factor for development of effective sex estimation methods. The aim of the study was to investigate the sexual dimorphism in the size and shape of the viscerocranium using geometric morphometric techniques. It also aimed to explore the sex differences in distinct viscerocranial regions and to establish the most dimorphic region with regard to size and shape. Computed tomography images of 156 males and 184 females were used in the study. Three-dimensional coordinates of 31 landmarks were acquired. Five landmark configurations were constructed from the viscerocranium and its orbital, nasal, maxillary, and zygomatic region. Generalized Procrustes superimposition, principal component analysis, and discriminant analysis were applied to each configuration. The significance of the sex differences in size and shape was assessed and significant differences were found in all configurations. The highest accuracy was obtained from both shape and size of the whole viscerocranium. Based on size only, the highest accuracy was achieved by the nasal region. The accuracy based on shape was generally low for all configurations, but the highest result was attained by the orbital region. Hence, size is a better sex discriminator than shape.

Variation of bone layer thicknesses and trabecular volume fraction in the adult male human calvarium

The human calvarium is a sandwich structure with two dense layers of cortical bone separated by porous cancellous bone. The variation of the three dimensional geometry, including the layer thicknesses and the volume fraction of the cancellous layer across the population, is unavailable in the current literature. This information is of particular importance to mathematical models of the human head used to simulate mechanical response. Although the target geometry for these models is the median geometry of the population, the best attempt so far has been the scaling of a unique geometry based on a few median anthropometric measurements of the head. However, this method does not represent the median geometry. This paper reports the average three dimensional geometry of the calvarium from X-ray computed tomography (CT) imaging and layer thickness and trabecular volume fraction from micro CT (μCT) imaging of ten adult male post-mortem human surrogates (PMHS). Skull bone samples have been obtained and μCT imaging was done at a resolution of 30 μm. Monte Carlo simulation was done to estimate the variance in these measurements due to the uncertainty in image segmentation. The layer thickness data has been averaged over areas of 5mm(2). The outer cortical layer was found to be significantly (p < 0.01; Student's t test) thicker than the inner layer (median of thickness ratio 1.68). Although there was significant location to location difference in all the layer thicknesses and volume fraction measurements, there was no trend. Average distribution and the variance of these metrics on the calvarium have been shown. The findings have been reported as colormaps on a 2D projection of the cranial vault.

Head circumference: the forgotten tool for hydrocephalus management. A reference interval study in the Spanish population

INTRODUCTION

In children, deviations from the normal range of head circumference (HC) have traditionally been related with CSF dynamics abnormalities. In adults, this neglected parameter is helpful in the diagnosis and understanding of the pathophysiology of some CSF abnormalities. It has been demonstrated that HC is related to height. Because humans have increased in stature dramatically during the last 50 years, pediatric charts for head growth physiology and normal HC values in adults should be reevaluated.

OBJECTIVES

The main aim of the present study was to assess HC in a series of 270 normal healthy Spanish adults and to determine any differences between sexes and age groups. A secondary aim was to discuss the relevance of this parameter in the management of hydrocephalus in adult people.

METHODS

HC measurements were taken using a measuring tape placed over the greatest frontal and occipital protuberances. The reference interval and the upper and lower thresholds for HC were calculated by 3 different methods: normal distribution, the non-parametrical percentile method, and the "robust method".

RESULTS

The results were consistent and showed that Spanish adult men with a HC greater than 60 cm, and Spanish adult women with a HC greater than 58 cm should be considered macrocephalic. Microcephaly should be considered when HC is 53.6 cm in men and 51.3 cm in women. Adult age groups of either sex do not present any statistically significant differences in HC.

CONCLUSIONS

HC obtained in Spanish adult people are greater than those reported in the classical Nellhaus graphs in both men and women aged 18. These findings should be considered in the management of hydrocephalus in adults today.

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.

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.

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.

Age related changes in intracranial volume in rabbits with craniosynostosis

Neurocapsular growth is highly heritable and determines neurocranial form. Although craniosynostosis alters brain growth direction, resulting in compensatory changes in the neurocranium, it is believed that such compensations occur without reduction in intracranial volume. This hypothesis was tested in a rabbit model with nonsyndromic, familial coronal suture synostosis. Skulls of 56 rabbits (20 normals, 20 with delayed onset synostosis, and 16 with complete synostosis) were scanned using three-dimensional computed tomography at 6 and 18 weeks of age. Intracranial contents were reconstructed, and indirect intracranial volume was calculated. Qualitatively, re-formations of intracranial contents from completely synostosed rabbit skulls exhibited the typical "copper beaten" morphology. Quantitatively, intracranial volume was significantly (p < 0.05) reduced in rabbit skulls with complete synostosis compared with both control rabbit skulls and rabbit skulls with delayed onset synostosis at 6 weeks by 11 percent and 14 percent, respectively). By 18 weeks, intracranial volume in rabbit skulls with synostosis was significantly (p < 0.05) reduced (by 12 percent in complete synostosis and 8 percent in delayed onset synostosis) compared with normal rabbits. Results suggest that in rabbits with uncorrected craniosynostosis, compensatory changes in the neurocranium were not adequate to allow normal expansion of the neurocapsular matrix. Further research is needed to determine whether reduction in intracranial volume was a result of neural tissue deficiency or cerebrospinal fluid (i.e., ventricular or subarachnoid) space compression in this model.

Can frontal sinus development be used for the prediction of skeletal maturity at puberty?

The precision of a new procedure predicting skeletal maturity on the basis of frontal sinus development was tested in 59 boys with an Angle class-II division-1 malocclusion. Lateral head films were used for the analysis of frontal sinus development, and handwrist radiographs were used for the assessment of skeletal maturity. The results showed that skeletal maturity could be predicted with a certainty of about 85% when using a 1-year prediction interval and with a certainty of about 75% when using a 2-year prediction interval. In conclusion, the study showed that skeletal maturity can be predicted with rather high accuracy by means of the analysis of frontal sinus development as imaged on lateral headfilms.

An investigation into the age of cessation of endocranial growth using the techniques of logetronic copying and photosubtraction

The classical teaching that endocranial growth is dependent on growth of the brain and thus should cease early in life has been questioned by Richardson and Blair who found marked expansive growth between 5 and 15 years in the occipital region. These authors were unable to comment on the age at which endocranial growth ceases because the changes towards the end of the growth period were of the same order of magnitude as the errors involved in digitizing standard cephalometric radiographs. In the present study, aimed at determining the age of cessation of endocranial growth, a very precise technique involving Logetronic copying and photosubtraction was used. Positive and negative Logetronic prints were made from standard 90 degree lateral cephalometric films of 28 normal boys taken at annual intervals between 5 and 15 years. The negative of one stage superimposed on the positive at the next stage revealed any growth changes by photosubtraction. Comparisons were made between films at 5 and 10 years, 10 and 13 years, 13 and 14 years and 14 and 15 years. All superimpositions and recordings were repeated by a second observer. All subjects showed growth changes between 5 and 10 years, 96% changed between 10 and 13 years, 64% changed between 13 and 14 years, and 54% showed growth changes between 14 and 15 years. Endocranial growth has ceased between 14 and 15 years in 46% of normal boys.

Diachronic variation in cranial thickness of Near Eastern populations

Cephalometric radiographs were taken of 111 skulls of skeletal remains of populations living in Israel and Jordan during the last 12,000 years. From these radiographs, skull length and height, and cranial thickness were measured. For each sex and period, high correlations were found between cranial thickness at vertex, bregma, and lambda. Cranial thickness at nasion was correlated with sinus width but not sinus height. All measurements were correlated with skull length but not skull breadth. Using multivariate analysis, no significant differences in cranial thickness were found between the sexes. Significant diachronic trends were found in lambda and sinus width, and they were independent of variation in skull length.

Sexual dimorphism in the growth of the cranium

The major sexual dimorphisms in body size appear at puberty but, by then, 95% of the growth of the cranium is completed. As sexual dimorphism in the cranium is as great as for other parts of the body, this suggests that it must appear at an earlier age, and that cranium/body size ratios for the two sexes will vary during growth. Results from a longitudinal study of Montreal children are used to investigate this phenomenon. The effect is expressed quantitatively by proportional growth and growth velocity curves, based on the final size of boys, which show that the dimorphism indeed makes an early appearance. The data are also analyzed on an age scale relative to the ages of peak growth velocity in stature, derived from the individual growth curves. This shows that although there is a minor pubertal spurt in growth for the external cranial dimensions of boys, it contributes relatively little to the final dimorphism in cranial size. To summarize this aspect of growth, an index of cephalization is calculated: head length X head width/stature. Cross-sectional standards for the change of the mean index with age show a linear decline for boys and girls until puberty, with a constant difference between them. After puberty, the index becomes equal in the two sexes. Individual development curves for the index are however not linear.

Morphological cerebral asymmetries of modern man, fossil man, and nonhuman primate

Cerebral asymmetries are common in modern and fossil man and the great apes. Those occurring most often are listed here: 1. The left sylvian fissure in man is longer than the right and in both fetal and adult brains the posterior end of the right sylvian fissure is commonly higher than the left. Associated with these findings, the left planum temporale is usually longer than the right. 2. The left occipital pole is often wider and usually protrudes more posteriorly than the right. 3. The left lateral ventricle, and especially the occipital horn, is usually larger than the right. 4. If one frontal pole extends beyond the other it is usually the right. 5. On X-ray computerized axial tomograms (CT) of the brain the right frontal lobe and the central portion of the right hemisphere more often measure wider than the left. 6. The CT studies commonly show a Yakovlevian anticlockwise torque (taking the nose as 12 o'clock), with the left occipital pole longer and often extending across the midline toward the right and a wider right hemisphere in its central and frontal portions and frequent forward protrusion of the right frontal pole. This is found also in newborns. 7. The posterior end of the sagittal sinus usually lies to the right of the midline and the sinus flows more directly into the right transverse sinus than into the left. 8. The right transverse sinus is usually higher than the left. 9. In left-handed and ambidextrous individuals the posterior ends of the sylvian fissures are more often nearly equal in height and the occipital regions are more often equal in width or the right may be wider. 10. The torque of the pyramidal tract and the hemispheral torque cannot at present be related to right- or left-handedness. Statistics concerning left-handedness are somewhat confounded, because it is likely that not a few individuals are left-handed because of an early injury of the left hemisphere in a normally right-handed individual. 11. Cerebral asymmetries are found in fossil man similar to those in modern man. 12. Asymmetries of the sylvian fissures similar to those of modern man have been found in the great apes and are particularly common in the orangutan. 13. The most striking and consistently present cerebral asymmetries found in adult and fetal brains are in the region of the posterior end of the sylvian fissures-- the areas generally regarded as a major importance in language function.

Thickness of the normal skull in the American Blacks and Whites

Normal skull thickness has been measured in a general hospital population of 300 blacks and 200 whites in America. In both groups, there is a rapid increase in skull thickness during the first two decades of life, followed by a small uniform increase reaching a peak in the fifth and sixth decades. The sex differences are variable, but in certain age groups the females in both races have significatly thicker parietal and occipital bones than their male counterpart. The frontal bone is thicker in the white male than in the black, and the parietooccipital thicker in the blacks than in the whites. Some suggestions are offered to explain the sex and racial difference noted.