Role of cranial sutures in normal and abnormal skull development.

In a series of experimental studies, the effects of induced premature closure of a normal cranial suture on the normal growth pattern of the rabbit skull are reported. In general, the results indicate that the craniofacial skeleton is an integrated growing unit in which alteration in growth of one component has profound effects on growth of other components. The magnitude and type of compensatory response depend on the type of suture, i.e., cranial or facial, its location, and timing of the growth insult. It is also important to note that the timing of surgical intervention has a direct effect on the capability of the growing craniofacial skeleton to obtain a more typical growth pattern.

Restricted growth at the frontonasal suture: alterations in craniofacial growth in rabbits.

Apposition of bone at the sutural margin is generally thought to be a compensatory adjustment to growing soft-tissue organs such as the brain or eyes within the skull. The frontonasal suture which is located at the interface between the cranial and facial skeletons is a site of extremely active growth in the young rabbit. Recently, we showed that premature closure of a cranial suture, the coronal suture, can alter the growth not only at the adjacent frontonasal suture but also of the basicranium and midface. This study examines the effects of restricted growth at the frontonasal suture on both growth at adjacent cranial sutures and linear growth of the basicranium and midface. Thirty newborn New Zealand White rabbits were subdivided into experimental and sham-treated groups of equal size and distribution for sex and birth weight. At 9 days of age, the frontonasal suture of each experimental animal was immobilized by bilateral application of methyl-cyanoacrylate adhesive across the frontonasal suture. Growth and morphometric changes were monitored by radiocephalometric methods through 120 days of age by bilateral implantation of radiopague markers on each side of frontonasal, coronal, and anterior lambdoid sutures. Results indicate that restricted growth at the frontonasal suture results not only in a significant shortening of the midface but also in significant decreases in growth at the coronal and internasal sutures. Growth at the interfrontal and sagittal sutures is increased. Furthermore, growth at the anterior portion of the nasal bones is significantly increased, thereby offsetting a portion of the decreased nasal bone length resulting from frontonasal restriction.

Skull expansion in experimental craniosynostosis.

Bilateral coronal suture immobilization was performed in 9-day-old rabbits to simulate the brachycephaly deformity characteristic of coronal synostosis. Growth abnormalities were documented by serial radiographic cephalometry. A "corrective" linear craniectomy procedure was performed on the rabbits with an immobilized coronal suture at 60 days of age. The degree of amelioration of the induced abnormalities by the surgery in these animals was compared with a similar group of animals that had the same surgery plus supplemental implantation of a spring expansion device at the coronal suture craniectomy site. The mean marker separation at the coronal suture was significantly greater (5.61 mm +/- 0.52 SE versus 2.53 mm +/- 0.38 SE; p less than 0.05) following spring expander implantation than with linear craniectomy alone. Similarly, induced anterior cranial base shortening and distortion of craniofacial cephalometrics were more significantly improved by the additional use of the spring expansion device.

Experimental unilateral coronal synostosis in rabbits.

Immobilization of the coronal suture was produced unilaterally in 9-day-old rabbits to determine its effect on subsequent craniofacial development. The suture was immobilized unilaterally by the topical application of methylcyanoacrylate adhesive. Subsequent growth effects on the cranial vault, base, and facial skeleton were assessed by serial radiographic cephalometry. Unilateral coronal suture immobilization resulted in significantly decreased bone growth at the coronal suture (mean 0.95 mm +/- 0.35 SE) when compared to sham-treated control animals (mean 5.06 mm +/- 0.20 SE). Frontonasal suture bone growth contralateral to the immobilized half of the coronal suture, however, was significantly increased. The anterior cranial base became significantly shortened, and orbital asymmetry developed. The pattern of induced abnormalities simulates unilateral coronal synostosis in humans.

Palatal anteversion as part of the iniencephaly malformation sequence.

We describe a fetus with hydrocephalus and the cranial and cervical findings of iniencephaly (enlarged foramen magnum, fusion of the upper cervical vertebrae, and a retroflexed, webbed neck) who had an unusual palatal abnormality ("palatal anteversion"). The posterio-lateral border of the secondary palate arose at the oral commissures, giving the palate an appearance of being folded so that the uvula was directed anteriorly. There were no clefts. Histologic sections of the junction of the secondary palate with the inner aspect of the oral commissures revealed continuity of the epithelial basement membranes and no unusual disarray of collagen fibers. This indicates that the unusual palatal orientation occurred during palatal formation and was not due to adhesion formation later in development. Failure of rotation of the palatal shelves prior to fusion and merging could account for the observed findings.

Compensatory growth following premature closure of the coronal suture in rabbits.

Premature closure of a cranial suture results in skull deformation characterized by inhibited skull growth in a direction perpendicular to the course of the affected suture. Early surgical release of the closed suture results in a "normal" skull morphology. The present experimental study measured alterations in growth at the transverse cranial sutures that occurred following induced premature closure of the coronal suture and its subsequent release in New Zealand White rabbits. Using roentgenocephalometric methods, growth and morphometric changes were monitored at the frontonasal, coronal, and anterior lambdoid sutures following premature closure of the coronal suture at 9 days of age. The results indicated that premature closure of the coronal suture did not result in compensatory (increased) growth at the other transverse sutures of the vault. In fact, growth at these sutures was significantly reduced. This reduced growth at adjacent transverse sutures was not ameliorated by early surgical release of the fused suture.

Skull growth after coronal suturectomy, periostectomy, and dural transection.

Using radiocephalometric procedures, the authors examined the separate effects of suturectomy, periostectomy, and dural transection on the growing skull in young rabbits. When the coronal suture was surgically removed during normal growth, The freed frontal and parietal bones separated at a significantly accelerated rate. No accelerated separation was found when only the overlying periosteum and aponeurosis were transected. Furthermore, no additional separation was observed when the dura mater and falx cerebri were transected following suturectomy. Analysis of growth at the adjacent frontonasal and anterior lambdoid sutures suggested that the accelerated separation of bones after suturectomy was compensated for by reduced growth at these adjacent sutures. The result of these compensatory actions was that the total length of the skull remained unchanged. This study not only supports earlier observations that sutures grow in response to extrinsic separative forces but, significantly, that the suture tissue itself, rather than the dura or pericranium, acts as a restraint during normal translatory growth.

Age as a critical factor in the success of surgical correction of craniosynostosis.

The effect of timing of the surgical release of prematurely immobilized coronal sutures was studied in rabbits. At 9 days of age, the coronal suture was mechanically immobilized by the application of methyl cyanoacrylate adhesive. These animals and a control group then received metallic implants on each side of the suture to monitor growth. At 30, 60, or 90 days after suture immobilization, separate groups of animals underwent a linear suturectomy to release the restriction. In animals in which the suture was not released, growth at the coronal suture was significantly restricted and resulted in severe deformities in the neurocranium. The benefits derived from surgical release were time-dependent. Suturectomy at 30 days of age resulted within 60 days in achievement of 100% of the growth in sham-treated controls. In contrast, delayed surgery at 60 or 90 days of age resulted in achievement of only 38% and 17% of normal growth, respectively. Angular measurements of the vault and base of the cranium showed a similar graded response toward normality, with the greatest correction occurring with the earliest operation. These results support the clinical impression that early surgical correction of craniosynostosis results in superior cosmetic appearance. A further implication of this work is that abnormality at a single suture strongly influences the development of other areas in the craniofacial complex.

Adjacency effects in developmental correlations among tooth organs in human fetuses.

This study explores whether the "distance gradient" model shown for embryonic development and postnatal tooth growth is also characteristic of the fetal period. Histologic data and ratings from 26 human fetuses show that, unlike the embryonic and postnatal periods, changes occurring in two tooth germs are significantly alike, regardless of the number of intervening teeth.

Nutritional influence on childhood development and genetic control of adolescent growth of Quechuas and Mestizos from the Peruvian lowlands.

The growth in height of 1,202 Quechua and Mestizo children aged 6 to 19 years of the province of Lamas in the Peruvian Eastern Lowlands was studied. As shown by evaluations of ABO, Rh systems, and skin reflectance measurements, the Quechuas are genetically different from the Mestizos. The heights of Quechuas and Mestizos were matched for nutritional status based on measurements of subcutaneous fat and body muscle. The study indicates that: 1) during childhood, Quechuas and Mestizos matched for the same nutritional status attain similar heights; 2) during adolescence (or after the age of 11 years), the Mestizos are significantly taller than the Quechuas of the same nutritional status; 3) during childhood, the relative difference in height between Quechuas and Mestizos matched for the same nutritional status is less than the difference between Quechuas (or Mestizos) of the same genetic composition characterized by good and poor nutritional status. These findings suggest that the influence of environmental factors, such as nutrition, have a greater influence in producing differences in body size during childhood than during adolescence. Conversely, the present findings support the hypothesis that the influence of genetic factors on body size are greater during adolescence than during childhood. However, comparison of adolescent samples of similar genetic composition (whether they be Quechuas or Mestizos), characterized by good and poor nutritional status, reveal large differences in height, suggesting that under conditions of malnutrition, the genetic control of growth is diminished.

Crown size-arch space relationships during human prenatal dental development.

As shown in composite reconstructions made from optically-projected measurements of 10mu frontal maxillofacial sections of 20 histologically normal fetuses and embryos in the 70-255 mm CRL range, individual differences in relative tooth size and interdental spacing are evident by 10.5-11 weeks of gestation, and age-corrected crown-size correlations (r=0.40) approximate those in postnatal life. Despite an eight-fold increase in crown dimensions, interdental spacing remains approximately constant after 150 mm CRL, suggesting that the tooth organs or the periodontal membranes are able to maintain spacing, into the third trimester.