The purpose of craniomaxillofacial surgery is to improve function, occlusion, craniofacial balance, and aesthetics. Accurate diagnosis, assessment, and careful treatment planning are essential in achieving a successful outcome, and an understanding of the pattern of facial growth is integral in this process. Patients with craniofacial congenital dysmorphologies, posttraumatic asymmetries, or disturbances of facial balance from radiation may have functional and/or aesthetic issues that require treatment. Understanding the complexities of growth in the skull and face is a key component to appropriate treatment planning for these disorders. This article reviews growth and development in the craniofacial skeleton.
Dysmorphologies may result from congenital malformations, trauma, radiation, or iatrogenic disturbances.
Most orbital growth is completed by 5 to 7 years of age, making it the optimal time to reconstruct deformities in this area for a more definitive result. Growth of the zygoma and maxilla is initially slower than the cranial-orbital region; however, most growth is complete by 7 years.
Malposition of the mandible is usually reserved until cessation of growth; however, a surgeon may consider mandibular advancement in a growing patient with severe airway obstruction or obstructive sleep apnea, to improve the overall growth vector of the face and for psychological reasons.
Risk factors for relapse after surgical mandibular intervention in a growing patient include high mandibular plane angles, preexisting condylar disorders, and advancements of 10 mm or greater.
After surgical intervention for vertical maxillary excess in the growing patient, the vertical growth of the maxilla may continue, with a high risk for clockwise mandibular rotation, relapse, and development of an anterior open bite.
The goals of craniomaxillofacial surgery include establishing a stable morphology and improving facial aesthetics. Dysmorphologies or deformities may result from congenital malformations, trauma, radiation, or iatrogenic growth disturbances. The surgical treatment designed to treat these disorders may necessitate manipulation of the soft tissues or bony structures based on the particular deformity or dysmorphology. For example, the failure of fusion that creates facial clefting is usually repaired in infancy during the growth phase. Just repairing these soft tissues in key growth areas may have negative consequences later in life. Radiation or trauma at an early age may cause hypoplasias and asymmetries that require treatment at different stages of growth. The interplay between the different growth areas of the facial structures highlights the possible biologic consequences of early intervention during the growth phase.
When skeletal discrepancies exceed the envelope of those that can be appropriately treated with orthopedic growth modification and/or orthodontic compensation techniques, surgical repositioning of the craniofacial structures may be indicated. In many instances, patients with skeletal deformities benefit from surgical correction following the completion of facial growth. This approach allows a definitive treatment that is highly predictable and stable in most cases. In contrast, surgical treatment performed before skeletal maturity is less predictable and may require reoperation following skeletal maturation. However, early intervention may be warranted for functional or aesthetic reasons, but the hoped-for advantage of early surgical interventions to unlock growth has not been realized, and, in most cases, there are no clear benefits to early operative intervention. These common issues emphasize the importance of considering growth when planning surgical treatment.
This article reviews the concepts of growth and development in the craniofacial skeleton as they relate to the treatment of soft tissue and skeletal dysmorphologies. The basic principles of craniofacial growth are reviewed, and the specific patterns of craniofacial dysmorphologies are discussed with regard to potential early and/or staged intervention. A balanced approach to treatment planning is presented with growth as the primary factor to consider. However, functional aspects of the airway and occlusion are of considerable importance in some patients. Certain clinical situations require intervention, even at the cost of iatrogenic disruption of growth potential, when there is a significant benefit perceived. In addition, aesthetic concerns in patients with severe deformity often require early intervention for psychosocial reasons.
Growth discrepancy and the craniofacial skeleton
Growth discrepancies involving the craniofacial skeleton are common, and many of these discrepancies can be managed with orthopedic growth modification and/or orthodontics alone if they are not severe. In particular, congenital craniofacial malformations, deformities, and pathologic or traumatic disruptions may have severe skeletal dysmorphologies and discrepancies. For example, deformational plagiocephaly causes cranial and possibly orbital asymmetry that, when diagnosed early, is treated with a form of growth modification using custom-molding helmets or bands. In instances when the discrepancy is particularly large or other deformities of the cranio-orbital region are encountered, surgery may be helpful to dismantle the craniofacial components and reposition them in a more normal conformation. There are several examples of skeletal and soft tissue discrepancies that occur in childhood requiring treatment. Deciding when to intervene is important to optimize the long-term results for these clinical challenges.
Growth abnormalities and dysmorphology of the lower face are the most commonly encountered clinical problems for the craniomaxillofacial surgeon. When these discrepancies involve the teeth, most minor discrepancies are treated with orthodontic compensation. However, some are beyond the envelope of orthodontic compensation techniques and may benefit from surgical repositioning of skeletal components. Orthognathic surgery for the treatment of skeletal discrepancy and malocclusion has traditionally been undertaken following the completion of growth, and there is substantial literature regarding the effects and stability of these procedures. However, there are only a limited number of studies that have investigated the outcome following orthognathic, craniofacial, or other types of maxillofacial surgery performed in the growing child. The supposition that surgical intervention before skeletal maturation may inhibit the future growth potential of the involved bone is long-standing. This concept is, in part, based on studies of patients with cleft lip and palate deformities, Robin sequence, craniofacial microsomia, Treacher Collins syndrome, and a range of other conditions in those who had undergone surgical procedures during growth. Data regarding growth consequences are lacking in areas of posttraumatic and radiation deformity. Empirical evidence reveals that many patients suffer asymmetry caused by soft tissue scarring and bone growth abnormalities associated with significant trauma or radiation. The results and observations from these studies provide information about growth potential; however, is it important to recognize that these patients also have underlying dysmorphologies or disorders that may influence facial growth, independently of surgical correction. In the assessment of subsequent facial growth problems, it is difficult to delineate between that related to the preexisting condition with its aberrant growth pattern and that potentially caused by the surgical osteotomy or other manipulations. Early surgery has usually been reserved for individuals with marked skeletal dysmorphologies and/or severe functional concerns (eg, intracranial pressure increases, choanal atresia, or severe obstructive sleep apnea). The presence of severe functional problems or implications for the psychosocial development of the child may become important when considering early surgery. A firm understanding of the patterns of facial growth is essential when planning surgical reconstruction.
There is some predictability to the growth of the cranium and face, but individual variation and pathologic conditions must be considered. Common growth variations (eg, vertical maxillary excess with mandibular hypoplasia) and pathologic clinical situations (eg, maxillary hypoplasia in the patient with a cleft palate) should be recognized, and treatment planned and then staged with these issues in mind. Clinicians must be aware of these early discrepancies, not to force early intervention in most cases but to develop a diagnosis and stage the reconstruction for the most predictable result. Treatment plans can then be formulated based on the best estimation of the expected pattern of growth.
Concepts of craniofacial skeletal growth and development
Craniofacial development, growth, and remodeling are a complex interplay of structure and function beginning in the embryo and continuing throughout adult life. The delicate equilibrium that exists between various parts of the craniofacial skeleton is stimulated by genes and local function that coordinate complex biomechanical and molecular signaling to yield a composite skeletal form. Problems can occur at anytime during this process and negatively affect the development and growth process. Understanding the basic biology of craniomaxillofacial growth is essential when planning treatment of malformations, disruptions, and deformities. The basic definitions of growth are important to understand when discussing the biology of growth and development ( Table 1 ).
|Dysmorphology||Abnormal morphology of tissues|
|Malformation||Formation of tissue is poor as a result of an intrinsic problem with development|
|Disruption||A breakdown in normal tissue development causing abnormal morphology|
|Deformation||Changes in morphology caused by external forces on normal tissue|
|Growth||Increase in cell size (plasia) or cell number (trophy)|
|Remodeling||Compensatory or adaptive changes of tissue|
|Development||Increase in complexity|
|Hypertrophy||Increase in the size of the cells|
|Hyperplasia||Increase in the number of cells|
In general, there is a cephalocaudal growth vector that occurs throughout early life and facial development that is thought to be closely linked to the functional demands of each region ( Fig. 1 ). Enlow discussed the concepts of growth in detail and outlined the 2 main morphologic events that direct craniofacial growth. These include (1) basal cranium growth and (2) development of the pharyngeal and facial airway structures. This vector of cephalocaudal growth is directly related to the changes seen in the proportions of the head and face during early life. In the early phase, this is reflected in the relative importance of cranial growth as a response to the rapid growth of the brain tissues. This response occurs in the neurocranium, which houses the structures of the brain, orbits, and olfactory system, and this region comprises the cranium and upper third of the face. The remainder of the facial tissues accelerate their growth at a later phase as the airway and muscles of mastication increase their function. This region represents the viscerocranium ( Table 2 ).
|Average Adult % Completed by Age 1 y||Average Adult % Completed by Age 5 y||Average Age at Maturity (y)|
|Cranium||84–86||90–94|| Boys, 14
|Zygoma||72||83|| Boys, 15
|Maxilla||75–80||85|| Boys, 15
|Mandible||60–70||74–85|| Boys, 16
The bones of the craniofacial skeleton grow and develop by remodeling and displacement throughout young life. Remodeling occurs as a result of local factors that result in the change in the size and shape of various components of the facial skeleton. Displacement occurs by bones that move apart at the joint, suture, or articular regions. This displacement occurs away from the articular surfaces (ie, cranial sutures, temporomandibular joints, or maxillary sutures). Bone growth is modulated through this process by augmenting or diminishing various regions in response to the functional needs and the timing of gene expression. The 2 processes of remodeling and displacement should occur in a coordinated and interdependent fashion. If the processes are balanced, the skeleton develops appropriately. In contrast, if the balance is disturbed, such as by nasal obstruction or prenatal cranial suture fusion, the skeleton develops outside the envelope of equilibrium, resulting in a skeletal discrepancy.
Local signaling seems to occur between the bony components of the face to develop each area in response to the increasing functional demands of mastication and breathing. The orbits, maxilla, and mandible are dependent on one another early in this phase, whereas the cranial base has a more intrinsic or genetically based control mechanism. The cranium and orbits develop in response to the rapid growth of the brain and globes, which occurs during the first year of life, and hence the cranio-orbital complex is much larger than the maxillomandibular complex in infancy. The early developing neurocranial complex creates a craniocaudal growth vector that is clockwise in direction when viewing the right lateral skull. Later, the functional demands of mastication and deglutition on the mandible become more significant, and the nature of the equilibrium balance with the maxilla is also altered in response to the growth and development of the airway and the functional needs of mastication and speech development. Constant modifications to this process are made throughout growth and development to obtain a functional state of equilibrium. This interplay drives the growth process from cephalad to caudad.
The equilibrium of the craniofacial complex is altered following a series of normal developmental events:
Central neurologic development
Optic pathway development
Speech and swallowing development
Airway and pharyngeal development
Facial expression and muscular changes
Tooth development and exfoliation.
Each region has a unique growth curve, and there are various peaks of growth velocity that alter craniofacial equilibrium and result in skeletal growth changes to restore this equilibrium. It is essential to have an understanding of each region when deciding the timing of various reconstructive efforts. In general, more definitive corrections are performed later in the growth phase and, ideally, should be undertaken at the completion of growth because earlier intervention may alter the growth curve and disrupt the equilibrium. Relapse toward the original deformity or dysmorphology is more likely to occur when the body attempts to restore the balance that has been altered by surgical intervention performed before skeletal maturation.
Regions of craniofacial growth and development
The cranium is made up of the chondrocranium and the neurocranium. The chondrocranium, or cranial base, develops initially in cartilage derived from occipital somites and then becomes bone by endochondral ossification. These ossification centers form the bones of the base of the skull, (ie, the occipital, sphenoid, temporal, and ethmoid bones). Growth of the cranial base bones occurs interstitially at articulations called synchondroses. Although most of the growth is occurring at the synchondroses, once ossified, the inner and outer surfaces of each bone can also remodel via appositional growth.
The neurocranium, or cranial vault, is made up of large and small curved, flat bones that are formed intramembranously, most of which are derived from neural crest cells. The growth of these bones occurs interstitially at the fibrous articulations (ie, the sutures) and appositionally on the endocortical and ectocortical surfaces. The cranial vault grows rapidly in the first year of life, and the velocity of growth plateaus in the following 5 years. A diploic space is present between 2 clear cortices of bone in most children between the ages of 2 and 5 years. Most growth in this area is complete by ages 5 to 7 years. At 1 year of age, the width of the head is 84% of its adult size, and, at 5 years of age, the head width increases to 93%. Head circumference is similar, with 86% of the growth complete by 1 year of age and 94% of growth completed by 5 years of age. The maturation age of the cranium width is 14 years in girls and 15 years in boys. The large amount of growth within the first 5 years of life reflects the neurodevelopment that occurs during this time.
Craniosynostosis is the premature fusion of cranial vault sutures, which is generally an antenatal event that causes growth restriction perpendicular to the affected suture. Craniosynostosis is most often seen with only 1 suture. However, craniofacial dysostosis syndromes occur when the cranial base synchondroses (primarily the presphenoethmoid synchondroses) and, to a lesser extent, the cranial vault sutures are affected to varying degrees. The alteration of the midface occurs in craniofacial dysostosis syndromes, such as Apert, Pfeiffer, and Crouzon syndromes. These syndromes are characterized by a restriction of growth in the anterior cranial vault and cranial base that results in severe orbital and midfacial hypoplasia and class III malocclusion. In addition, when the brain and cranial base components do not form in their normal fashion (eg, Binder sequence and Down syndrome), the development of the midfacial complex and the balance is also distorted.
Treatment of dysmorphology in the cranial vault and orbits is usually more definitive after 1 year of age because most growth in the cranium is complete at this time. In the case of craniosynostosis, surgical treatment is necessary earlier to allow appropriate volume for brain growth. For patients with craniofacial dysostosis in which skull base fusion has also affected the orbits and midface, this is treated at a later stage ( Fig. 2 ).
The orbits consist of bones from the cranio-orbital and nasomaxillary complexes, and most of the growth in the orbit region occurs at the sutures between these bones. The orbits grow rapidly in the first year of life in association with the globe, optic nerves, and neurocranial development, and the velocity decreases over the next 5 years. Most of the growth in this area is completed by 5 years of age. The intercanthal width at age 5 years is, on average, 30 mm, which is approximately 93% of the adult value. Intercanthal width is fully mature in boys at 11 years of age and in girls at 8 years of age. Orbital height grows at a more gradual rate compared with the other orbital dimensions. The impressive growth of this region before 5 years of age is a result of the rapidly developing globes and optic neurologic system.
Orbital dysmorphology is seen in unicoronal craniosynostosis, the craniofacial dysostosis syndromes, and also in patients who fail to obliterate the foramen cecum during development with midline lesions, such as gliomas, dermoids, or encephaloceles. The delicate balance is disturbed, and the tissues adapt based on the pathologic condition that is present. Most treatments are best performed after the age of 5 years ( Fig. 3 ).
The zygomatic bones grow rapidly in the first year of life and level off in velocity over the next 5 to 7 years. Growth in this area is initially more gradual compared with the cranium and orbits, but most of the growth in this area is similarly complete by age 5 to 7 years. The bizygomatic width is 83% of the mature adult size by the age of 5 years, and the width of the face is mature at 15 years in boys and 13 years in girls.
Zygomatic deformities are seen in Treacher Collins syndrome, craniofacial dysostosis syndromes, Down syndrome, achondroplasia, cretinism, and other growth restrictions of the cranial base. The hypoplasia is also evident in the maxilla and nasal complex. Definitive treatment in this area can usually be performed after the age of 5 years ( Fig. 4 ).
Much like the cranium, the maxilla develops by intramembranous ossification of neural crest cells. Maxillary growth is a result of early nasal septal growth and later by sutural growth and surface remodeling with a forward and downward displacement relative to the cranial base. Midfacial height (nasion to gnathion) reaches maturity at 13 years in girls and 15 years in boys. The most active times of growth are from the ages of 1 to 2 years and 3 to 5 years. The height of the midface (nasion to stomion) matures slightly earlier in boys at 14 years and 12 years in girls. Midfacial projection (tragus to stomion) reaches maturity at 14 years in boys and 13 years in girls.
The midfacial hypoplasia seen in craniofacial dysostosis syndromes, achondroplasia, and other disorders is impressive, often in all 3 dimensions. Nasomaxillary trauma in early childhood can also result in significant midface hypoplasia. Patients may develop severe anterior-posterior maxillary hypoplasia, transverse discrepancies, and anterior open bites. For these reasons, definitive correction of maxillary dysmorphology is usually reserved for after the ages of 14 years in girls and 16 years in boys once skeletal maturity has been achieved. When these deformities are particularly severe, early intervention is entertained, which may include attempts at growth modification (ie, reverse-pull headgear) or early midfacial advancement with osteotomies ( Figs. 5 and 6 ).
There is a classic notion that the condyle is the independent growth center of the mandible. Although the condyle is important in the growth and development equilibrium, the mandible develops by displacement and remodeling in all regions, not just the condyle. Periosteal apposition (eg, posterior ramus region), resorption (eg, anterior coronoid and ramus), and endochondral growth occur in the mandible. The coordinated apposition and resorption results in an inferior and anterior displacement of the mandible throughout the growth phase. Mandibular width is nearly 93% complete by the age of 5 years; however, it does not mature until 13 years in boys and 12 in girls. Mandibular depth (tragus to gnathion) is 85% complete at age 5 years; however, it does not reach the mature dimension until 15 years in boys and 13 years in girls. Mandibular height is 67% complete by 1 year and 88% complete by 5 years. Mandibular height is mature at 12 years in girls and 15 years in boys.
Marked alterations in the development of the mandible are found in Cornelia de Lange syndrome, Nager syndrome, Treacher Collins syndrome, and craniofacial microsomia ( Figs. 7 and 8 ). There is frequently severe mandibular hypoplasia yielding a class II malocclusion and a high mandibular plane angle, and there may be anomalies of the temporomandibular joint complex. In contrast, class III malocclusion and mandibular hyperplasia, particularly in the ascending ramus, is seen in syndromes such as acromegaly. Treatment of mandibular deformities is usually reserved until after the ages of 16 years in girls and 18 years in boys. Early intervention for severe deformities may include either growth modification devices or early osteotomies with or without distraction osteogenesis.
Clinical evaluation of craniofacial growth
There is considerable individual variation in the growth of the craniofacial skeleton, and many methods have been developed to assess the individual growth of patients considered for surgical treatment of a craniofacial deformity. The evaluation of the craniofacial skeleton can be performed by several simple methods based on both expected norms and concepts of growth and development. There are considerable data on the growth of the facial skeleton in patients without significant deformity or growth discrepancy. Individual measurements can be made and compared with existing age-matched control data to gain some information about the extent of the deformity. In comparison, there is a limited amount of data available on the various anomalies, and therefore only generalizations can be made with respect to the differences observed with the abnormal relationships.
Hand-wrist plain films have been used for many years to assess skeletal growth and to predict the maturation point of the craniofacial skeleton. The same process can be performed by analyzing the maturation of the cervical spine, and the predictive value of the cervical spine analysis has been purported to be similar to the hand-wrist technique.
One of the best methods to ascertain an individual's craniofacial growth is to evaluate serial cephalometric radiographs. Minimal or no change in velocity of the maxillofacial growth during adolescence is a good indicator of skeletal maturation. Cephalometric radiographs from the same machine using the same technique can be compared 6 or 12 months apart to evaluate for any significant change indicating growth.
Anthropometric measurements can be performed on individuals with calipers and correlated with normative data sets. These data can be helpful in determining either the amount of treatment to be undertaken or in evaluating the success of treatment. Posnick and others have evaluated individual types of deformities and the success of various surgical treatments using this type of approach, in addition to data generated from measurements performed on computed tomography (CT) scans. Although the measurements on CT are generally not practical for clinical practice, they are helpful in outcome assessment of the surgical correction. Computer-assisted surgery planning software allows superimposition of expected normative data or mirror-imaged data, which may be helpful in grossly evaluating comparative growth.
Surgical management considerations
Dysmorphology of the craniofacial skeleton is seen in patients with craniosynostosis of various types, including coronal, sagittal, metopic, and the various combinations of multiple-suture craniosynostosis. Craniosynostosis is an excellent example of the balance that is required when considering early treatment of a dysmorphology.
By definition, craniosynostosis is the early fusion of 1 or multiple sutures of the cranial vault, which causes both a telltale dysmorphology and a concern that the intracranial volume is less than the amount required for the rapidly developing brain. This mismatch can cause issues with brain growth, optic nerve function, and overall neurologic development. For this reason, expansion of the cranial vault is considered for some children with this disorder to both increase the volume available to the brain for growth and improve the dysmorphology caused by the restriction of cranial vault growth in the affected area.
The importance of brain growth requires that the surgeon consider the treatment of craniosynostosis before the ultimate maturity of the skull, but very early treatment is associated with marked relapse and the need for reoperation. For this reason, most surgeons tend to surgically dismantle the cranial vault before 1 year of age but after some growth has occurred; typically, this is beyond the 6-month time period. In cases in which multiple sutures are involved, the need for treatment is more urgent, and earlier treatment is considered knowing that additional cranial vault expansions will likely be required.
The need for revision surgery is higher in patients who have undergone very early treatment of cranio-orbital dysmorphology. The concept that early surgery may unlock growth has not proven to be sound based on the current understanding of craniofacial growth. However, delaying the surgical correction significantly may have adverse effects on brain development and optic nerve function. The exact timing remains controversial because no predictable and repeatable measure of either brain growth velocity or intracranial pressure is easily obtainable to allow the clinician to better judge the timing of surgical expansion.