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.

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.

Prenatal origins of carpal fusions.

As shown in 138 embryos and fetuses in the 40-285 mm crown-rump length range, carpal and carpal-metacarpal "fusions" arise from incomplete separation of the cartilaginous precursors rather than from failure of initiation, thus accounting for the "fusions" seen in postnatal radiographs and the grooves that are evident enough in adult fusions. Radiographs selected from over 20,000 apparently normal individuals provide postnatal counterparts for the prenatal examples shown in histological sections.

Prenatal origin of brachymesophalangia-5.

As shown in 91 embryos and fetuses in the 41-235 mm crownrump length, brachymesophalangia-5 may be identified in prenatal time. Although the ratios involving different combinations of length of mid-5 relative to other segments yield different frequencies of BMP-5, the short middle segment of the little finger is already associated with clinodactyly and developmental eccentricity as early as the ninth week of prenatal development.

Early prenatal attainment of adult metacarpal-phalangeal rankings and proportions.

As shown in 56 human embryos and fetuses between 15 and 104 mm in crown-rump length, "adult" metacarpal-phalangeal length rankings are attained by the seventh intrauterine week and near-adult bone-to-bone ratios or proportions by the theirteenth week. Micrometric measurements of optically-projected histological hand sections show relative elongation of the distals between the 15-29 mm and 30-44 mm crown-rump range, and relative reduction to radiogrammetrically-determined adult proportions by the 90-104 mm CRL.