Three-dimensional computed tomography cephalometry of plagiocephaly: asymmetry and shape analysis.

OBJECTIVE: To investigate facial asymmetry associated with both deformational and synostotic plagiocephaly and to identify variables based on skeletal landmarks that distinguish the conditions and quantify severity. DESIGN: Retrospective, cross sectional. SETTING: Australian Craniofacial Unit, Adelaide. MAIN OUTCOME MEASURES: Proportional differences between bilateral distances and principal component (PC) analysis of the skeletal landmarks. PATIENTS: The three-dimensional positions of 78 osseous landmarks were determined from computed tomography (CT) scans of 21 patients with deformational plagiocephaly (DP), 20 patients with unilateral coronal synostosis (UCS), and 2 patients with unilateral lambdoid synostosis (ULS). RESULTS: For both DP and UCS, significant asymmetry was found for the orbital depths, mandibular lengths, maxillary depths, zygomatic arch lengths, lateral base of the parietal bone, and the angle between the anterior and the posterior cranial base projected onto the axial plane. The small sample size for ULS precluded definitive statistical statements but allowed some useful comparisons with the other conditions. The first three PC scores were able to distinguish among the three conditions and which side was affected. CONCLUSIONS: The asymmetry of the cranial base and facial structures, arising from localized abnormality or deformational forces in either the frontal or the occipital regions, can be quantified by a plethora of bilateral features or summarized by PC analysis.

CT-determined intracranial volume for a normal population.

Intracranial volume comparisons of patients with craniosynostosis and normal have been contrary to expectations, leading to questioning of the validity of the current normal reference material. Computed tomography-determined intracranial volume is presented for a white normal population. Specifically, intracranial volumes for 157 subjects (82 female and 75 male) were measured from computed tomography data using the Cavalieri estimator: volume determination was based on measuring the area in each computed tomography section. Monomolecular and Gompertz models were applied to find curves of best fit to the intracranial volume as a function of the age. The best fit was obtained using the monomolecular model when the response variable was the logarithmically transformed intracranial volume, and the independent variable was the logarithm of the age from conception. For example, the mean (standard deviation) for male subjects at 1 year and 20 years were 1,125.6 (89.6) ml and 1,472.9 (117.2) ml, respectively, and for female subjects 1,024.9 (84.0) ml and 1,321.7 (108.3) ml, respectively. Although the shape and rate of increase of the female and male curves is similar, the female mean is 1.3 standard deviations below the male mean at 20 years. These curves were compared with the commonly referenced curves of Blinkov (1941), Lichtenberg (1960), and Dekaban (1977). Our male curve is substantially higher than these curves in the age range 8 months to 4 years. Our female curve, however, is approximately 1 standard deviation below Lichtenberg's curve from birth to 7 months. There are then only minor differences between our female curve and Lichtenberg's curve until his curve crosses ours at 41 months, where they significantly diverge from approximately 4.5 years. Our curves indicate that 95% of the final intracranial volume has been attained by 42 months for girls and 46 months for boys.

Bilambdoid and posterior sagittal synostosis: the Mercedes Benz syndrome.

A consistent pattern of craniosynostosis in the sagittal and bilateral lambdoid sutures is described in three patients. The external cranial ridging associated with fusion of these sutures produces a characteristic triradiate, or "Mercedes Benz," appearance to the posterior skull. Locally marked growth restriction is evident in the posterior fossa with compensatory secondary expansion of the anterior fossa manifesting a degree of frontal bossing which mimics bicoronal synostosis. Although this appearance could lead to inadvertent surgery in the frontal region, attention to the occipital region with wide early suture excision and vault shaping is indicated.

Computer tomography determined intracranial volume of infants with deformational plagiocephaly: a useful "normal"?

Over the last 10 years, children with deformational (nonsynostotic) plagiocephaly have undergone computed tomography scans using the same protocols as children with lambdoid craniosynostosis because of their similarly distorted head shapes. These children are believed to have normal intracranial volume. Given the recent questioning of what is the normal range of intracranial volume in human populations, the authors have undertaken a comparison of the intracranial volume of children with deformational plagiocephaly and Lichtenberg's normal population (Lichtenberg R. Radiographie du crane de 226 enfants normaux de la naissance a 8 ans: Impressions digitiformes, capacite, angles et indices [thesis]. Paris: University of Paris, 1960). The intracranial volume was determined for 20 females and 46 males with deformational plagiocepahly ranging in age from 2.5 to 20.7 months using computed tomography scan data. Although no significant differences were found for the females, the authors found that the intracranial volume of the males with deformational plagiocephaly were significantly larger than Lichtenberg's population. The authors conclude that this is because Lichtenberg's data do not adequately reflect the normal range of intracranial volume for males ranging in age from 2.5 to 20.7 months, rather than gender differences associated with deformational plagiocephaly. Further, until a more suitable normal becomes available, the deformational (nonsynostotic) plagiocephaly data could be used as substitute normal reference material in the measured age range for assessment of the intracranial volumes of children with craniosynostosis.

Computer generated mandibular model: surgical role.

A life-size nylon model of a traumatized mandible was produced from CT scan data by the process of laser sintering. The model was used for pre-operative planning and for production of surgical aids in order to facilitate the restoration of a large bony defect. Vascularized iliac crest bone was harvested, titanium implants placed and the bone then grafted to the mandible.

Extradural deadspace after infant fronto-orbital advancement in Apert syndrome.

Infant fronto-orbital advancement is presently a management cornerstone of the craniosynostosis in Apert syndrome. This procedure is based on the premise that the expanding brain rapidly advances in support of, and to remodel, the new frontal facade. This series of infant patients with Apert syndrome undergoing fronto-orbital advancement with early postoperative computerized tomography assessment reveals a large extradural deadspace persistent through the first postoperative week, not obliterated consistently until the fourth week. Early deadspace effacement results from expansion of the prefrontal subarachnoid space, without any significant change in size or shape of the frontal brain substance or ventricles. Brain growth or expansion was particularly slow with brain shape distortions still evident at late follow-up.

Central nervous system imaging in Crouzon's syndrome.

Although the need to prevent the secondary effects of craniosynostosis on the central nervous system is fundamental to the practice of craniofacial surgery, the detailed structural anatomy of the central nervous system in the syndromal craniosynostoses has become the subject of recent interest. A clinical and radiographic review of a population of 59 patients with Crouzon's syndrome determined the frequency of central nervous system deformities. Twelve percent of patients had evidence of decreased mental function. Ventriculomegaly on computed tomographic scan was present in 51% and found to be of three grades: mild, moderate, and severe (hydrocephalus). This was nonprogressive in 7 of the 11 patients with follow-up computed tomographic scans. Ten patients underwent surgical release to increase intracranial space; however, 6 of these patients showed no progression in ventricular size. Nonventricular anomalies were found less frequently (14%). Central nervous system findings show fewer nonventricular anomalies than in Apert's syndrome patients, with a corresponding higher mental function. The principal anomaly of ventriculomegaly is not directly related to suture defect and may represent a primary brain abnormality. Recommendations are made for the assessment and management of patients with Crouzon's syndrome with reference to these areas.

Noncraniofacial manifestations of Crouzon's disease.

Although most interest centers on the craniofacial region in Crouzon's disease, noncraniofacial manifestations are important because they may complicate both diagnosis and management. A population of 59 patients with Crouzon's disease was reviewed to determine the frequency of these deformities. Stylohyoid ligament calcification (50%) and cervical spine (40%) and elbow (18%) abnormalities were the most common. Minor hand deformities (10%), other musculoskeletal deformities (7%), and visceral anomalies (7%) were also seen. Acanthosis nigricans was not present in this population. Recommendations are made for the assessment and management of Crouzon's disease with reference to these areas.

The relationship between fracture severity and complication rate in miniplate osteosynthesis of mandibular fractures.

There are many factors influencing the outcome of mandibular fracture management; however, the relationship between fracture severity and complication rate has only been recognised intuitively due to the absence of an accepted system of classification of the severity of these fractures. In 1989 Cooter and David described the alpha numeric system of computer based coding for craniofacial fractures. Using this system, a prospective sample of 324 patients with mandibular fractures presenting to the Royal Adelaide Hospital was coded for fracture severity and their progress followed with respect to complication rate. A strong correlation between complication rate and fracture severity was established.

Mandibular lengthening by distraction for airway obstruction in Treacher-Collins syndrome.

Mandibular lengthening by distraction was performed in a 6-year-old tracheostomy-dependent Treacher-Collins syndrome patient. Detailed preoperative imaging revealed an occluded retrotongue base pharyngeal airway, which, following mandibular distraction, became patent and permitted tracheostomy removal. Mandibular distraction as a technique must be targeted toward clinical problems--management of upper-airway obstruction may be one such scenario.

Monocortical non-compression miniplate osteosynthesis of mandibular angle fractures.

The technique of monocortical non-compression miniplate fixation of mandibular angle fractures is reviewed. A study of our first 50 patients treated using this technique reveals that consistent reduction and stabilization of these mandibular fractures can be achieved without the requirement for intermaxillary fixation. Such results were produced with minimal postoperative morbidity.

Craniofacial osseous landmark determination from stereo computer tomography reconstructions.

The accurate and reproducible determination of the three dimensional (3D) co-ordinate positions of anatomical landmarks from computer tomography (CT) images has been limited even though potentially the data have been available for several years. This paper describes a method of acquisition of osseous landmark positions using an off-line computing technique based on multiple stereo images of 3D CT reconstructions. The use of stereo pairs greatly enhances the consistent identification of osseous landmarks. Further, the technique is of particular value where access to the CT scanner is restricted due to heavy clinical demand and separate high quality graphics facilities are unavailable. Osseous landmark position data were determined for dried skulls and patients with craniofacial conditions. Accuracies of the order 1.7mm (median) were obtained. These results encourage the use of the technique for acquisition of landmark positions for the study of the craniofacial complex in three dimensions.

Application and comparison of techniques for three-dimensional analysis of craniofacial anomalies.

Traditionally, cephalometric analysis has been limited to data determined from two-dimensional (2-D) cephalograms. With imaging facilities such as CT and biplanar radiography now available, the natural extension has been towards the use of three-dimensional (3-D) coordinate positions of landmarks for comparative purposes. While these data have been potentially available for several years, the accurate and reproducible extraction of anatomic landmarks suitable for comparative purposes has been limited. This paper presents results of the application of traditional comparative techniques to well determined 3-D coordinate data acquired from biplanar radiography and CT for a patient with Treacher Collins syndrome and further provides a comparison with the technique of strain analysis, often referred to as finite element analysis, which has been applied recently to craniofacial data. Comparisons of distances and angles between landmarks, landmark coordinate positions, and strains of the patient relative to experimental reference standards reveal that the essential skeletal features of Treacher Collins syndrome have been identified and quantified by the analysis techniques. Further, a measure of the significance of the deviations has been determined by comparisons with the experimental reference standards.

Computer-assisted location of reference points in three dimensions for radiographic cephalometry.

A major obstacle to the derivation of three-dimensional data from lateral and coronal radiographs of the head has been the lack of precision in locating the same landmarks on each of the biplanar images. The method described herein uses radiographic equations based on the geometry of a biplanar system to predict the location of a reference point on one film from its location on the other. This technique, which differs from previously described systems, allows a pair of cephalometric films to be digitized by an on-line procedure controlled by a personal computer. Three-dimensional coordinates of reference points are calculated and stored for subsequent retrieval when they can be used for metric analysis or for the display of simple wire-frame models of the skull. Computing algorithms are provided to aid software development.

Longitudinal study of dental arch relationships in Australian aboriginals with reference to alternate intercuspation.

The patterns of age change in dental arch breadths and depths were studied longitudinally in Australian Aboriginals, 92 males and 68 females. Three types of change in relative arch dimensions were recognized: a divergent pattern in which the differences between maxillary and mandibular dimensions increased with age, a convergent pattern in which the differences decreased, and a parallel pattern in which the arch differences remained metrically stable. The feature that best distinguished the Aboriginals from Caucasian groups was the high frequency of subjects, 71% of males and 40% of females, who showed a divergent growth pattern. The association between divergent growth in arch breadths and the development of alternate intercuspation, which is characterized by an inability to occlude the teeth on both sides of the arch at the same time, is discussed.

Age changes in dental arch dimensions of Australian Aboriginals.

Breadths and depths of the dental arches were measured from standardized photographs of serial casts of Australian Aboriginals enrolled in a longitudinal growth study. The data were obtained from 1161 sets of casts representing 111 boys and 86 girls ranging in age from 6 to 19 years. Age changes in the arch dimensions conformed to previously described patterns in Caucasian children, namely, an increase in breadth and a decrease in depth. Corresponding dimensions and dimensional changes in the maxilla and mandible were strongly correlated, but breadth and depth changes were relatively independent. The disparity in size between arches increased with age, particularly in the breadth dimension of boys. Marked disparity in arch breadths characterizes an occlusal feature of this population that has been termed alternate intercuspation.