Craniofacial Dysostosis Syndromes

Cranial vault sutures are a form of bone articulation in which the margins of the bones are connected by a thin layer of fibrous tissue. The cranial vault of an infant is composed of six major sutural areas and several minor sutures, which serve two critical functions during the postnatal period. Initially, the sutures allow head deformation during vaginal delivery as part of the birthing process. Later, during an infant’s postnatal development, cranial vault sutures facilitate head expansion to accommodate propulsive brain growth. Only a small amount of pressure (5 mm Hg) from the growing brain is required to stimulate bone deposition at the margins of a cranial bone. Under normal conditions, brain volume will triple within the first year of life, and by 2 years of age, cranial capacity is four times that at birth. Under normal circumstances, closure of the cranial vault sutures occurs earlier than closure of the membranous facial bone sutures, which often remain patent until adulthood.

The term craniosynostosis is defined as premature fusion of a cranial vault suture. With rare exception, this is an intrauterine event. Virchow, in 1851, coined the term craniosynostosis and formulated the classic theory known as Virchow’s law. This states that premature fusion of a cranial vault suture (craniosynostosis) inhibits normal skull growth perpendicular to the fused suture and that compensatory growth occurs at the open sutures. The general direction of growth after synostosis is parallel to the fused suture.

The term craniofacial dysostosis is used in a general way to describe syndromic forms of craniosynostosis. These disorders are characterized by sutural involvement that not only includes the cranial vault but also extends into the skull base and mid-facial skeletal structures. Craniofacial dysostosis syndromes have been described by Carpenter, Apert, Crouzon, Saethre and Chotzen, and Pfeiffer. Although the cranial vault and cranial base are thought to be the regions of primary involvement, there is also significant impact on mid-facial growth and development. In addition to cranial vault dysmorphology, patients with these inherited conditions exhibit a characteristic “total mid-face” deficiency that is syndrome specific and must be addressed as part of a staged reconstructive approach.

Functional Considerations

Restricted Brain Growth and Intracranial Pressure

If the rapid brain growth that normally occurs during infancy is to proceed unhindered, the cranial vault and base sutures must remain open and expand during the phases of rapid growth, with marginal ossification taking place. In craniosynostosis, premature fusion of the suture or sutures causes limited and abnormal skeletal expansion in the presence of continued brain growth. Depending on the number and location of prematurely fused sutures, growth of the brain may be restricted. In addition, abnormal cranial vault and mid-facial morphology occurs. If surgical release of the affected sutures and reshaping to restore a more normal intracranial volume and configuration are not performed, decreased cognitive and behavioral function is likely to be the end result.

Elevated intracranial pressure (ICP) is the most serious functional problem associated with premature fusion of sutures. Radiographic findings that may suggest elevated ICP include a “beaten-copper” appearance along the inner table of the cranial vault seen on plain radiographs and loss of brain cisternae observed on computed tomography (CT). Though suggestive of increased ICP, these are considered soft radiographic findings.

Increased ICP is most likely to affect patients with great disparity between brain growth and intracranial capacity and may occur in as many as 42% of untreated children in whom more than one suture is affected. Unfortunately, there is no absolute agreement on what levels of ICP are normal at any given age in infancy and early childhood.

The clinical signs and symptoms related to elevated ICP may have a slow onset and be difficult to recognize in the pediatric population. Although standardized CT allows indirect measurement of intracranial volume, it is not yet possible to use these studies to make judgments on those who require craniotomy for decompression. Careful neurosurgical and pediatric ophthalmologic evaluation is a critical component of the data-gathering process required to formulate definitive treatment plans in patients with craniosynostosis.

Vision

Untreated craniosynostosis with elevated ICP will cause papilledema and eventually optic nerve atrophy and result in partial or complete blindness. If the orbits are shallow (exorbitism) and the eyes are proptotic (exophthalmos), as occurs in the craniofacial dysostosis syndromes, the cornea may be exposed and abrasions or ulcerations could occur. An eyeball extending outside a shallow orbit is also at risk for trauma. If the orbits are extremely shallow, herniation of the globe itself may occur and necessitate emergency reduction followed by tarsorrhaphy or urgent orbital decompression.

Some forms of craniofacial dysostosis result in a marked degree of orbital hypertelorism that may compromise visual acuity and restrict binocular vision. Divergent or convergent non-paralytic strabismus or exotropia occurs frequently and should be considered during the diagnostic evaluation. This may be the result of congenital anomalies of the extraocular muscles themselves. Paralytic or non-paralytic unilateral or bilateral upper eyelid ptosis also occurs with greater frequency than in the general population.

Hydrocephalus

Hydrocephalus affects as many as 10% of patients with a craniofacial dysostosis syndrome. Although the cause is often not clear, hydrocephalus may be secondary to generalized cranial base stenosis with constriction of all the cranial base foramina, which has an impact on the patient’s cerebral venous drainage and cerebrospinal fluid (CSF) flow dynamics. Hydrocephalus may be identified with the help of CT or magnetic resonance imaging to document progressively enlarging ventricles. Difficulty exists in interpreting the ventricular findings seen on CT, especially when the skull and cranial base are brachycephalic. The skeletal dysmorphology present in a child with severe cranial dysmorphology related to craniosynostosis may translate into an abnormal ventricular shape that is not necessarily related to abnormal CSF flow. Serial imaging and clinical correlation are indicated, and a great deal of clinical judgment is often required in making these assessments.

Effects Of Mid-Face Deficiency on the Airway

All newborn infants are obligate nasal breathers. Many infants born with a craniofacial dysostosis syndrome have moderate to severe hypoplasia of the mid-face as a component of their malformation. They will have diminished nasal and nasopharyngeal space with resulting increased nasal airway resistance (obstruction). Affected children are thus forced to breathe through the mouth. For a newborn infant to ingest food through the mouth requires sucking from a nipple to achieve negative pressure, as well as an intact swallowing mechanism. A neonate with severe mid-face hypoplasia will experience diminished nasal airflow and be unable to accomplish this task and breathe through the nose at the same time. Complicating this clinical picture may be an elongated and ptotic palate and enlarged tonsils and adenoids. A compromised infant expends significant energy respiring, and this may push the child into a catabolic state (negative nitrogen balance). Failure to thrive results unless either nasogastric tube feeding is instituted or a feeding gastrostomy tube is placed. Evaluation by a pediatrician, pediatric otolaryngologist, and feeding specialist with craniofacial experience can help distinguish minor feeding difficulties from those requiring more aggressive treatment.

Sleep apnea of either central or obstructive origin may also be present. If the apnea is found to be secondary to upper airway obstruction based on a formal sleep study, a tracheostomy may be indicated. In rare situations, “early” mid-face advancement is useful to improve the airway and allow tracheostomy decannulation. Central apnea may occur as a result of poorly treated intracranial hypertension, as well as other contributing factors. If so, the condition may improve by reducing ICP to a normal range through cranio-orbital or posterior cranial vault decompression/expansion.

Dentition and Occlusion

The incidence of dental and oral anomalies is higher in children with craniofacial dysostosis syndromes than in the general population. In Apert syndrome in particular, the palate is high and constricted in width. The incidence of isolated cleft palate in patients with Apert syndrome approaches 30%. Clefting of the secondary palate may be submucous, incomplete, or complete. Confusion has arisen over whether the oral malformations and absence of teeth that are often characteristic of these conditions are a result of congenital or iatrogenic factors (e.g., injury to dental follicles associated with early mid-face surgery). The mid-facial hypoplasia seen in children with craniofacial dysostosis syndromes often results in limited maxillary alveolar bone to house a full complement of teeth. The result is severe crowding, which often requires serial extractions to address the problem. An Angle class III skeletal relationship in combination with an anterior open bite deformity is typical.

Morphologic Considerations

General

Examination of the patient’s entire craniofacial region should be meticulous and systematic. The skeleton and soft tissues are assessed in a standard fashion to identify all normal and abnormal anatomy. Specific findings tend to occur with particular malformations, but each patient is unique. Achievement of symmetry and normal proportions and reconstruction of specific esthetic units are essential to recreate an unobtrusive face in a child born with one of the craniofacial dysostosis syndromes.

Fronto-Forehead Esthetic Unit

The fronto-forehead region is dysmorphic in an infant with craniofacial dysostosis. Establishing normal position of the forehead is critical to achieve overall facial symmetry and balance. The forehead may be considered as two separate esthetic components: the supraorbital ridge–lateral orbital rim region and the superior forehead. The supraorbital ridge–lateral orbital rim region includes the glabella and supraorbital rim and extends inferiorly down each frontozygomatic suture toward the infraorbital rim and posteriorly along each temporoparietal region. The morphology and position of the supraorbital ridge–lateral orbital rim region are key elements of upper facial esthetics. In a normal forehead, at the level of the frontonasal suture an angle ranging from 90 to 110 degrees is formed by the supraorbital ridge and the nasal bones when viewed in profile. Additionally, the eyebrows, which overlie the supraorbital ridge, should be anterior to the cornea. When the supraorbital ridge is viewed from above, the rim should arc posteriorly to achieve a gentle 90-degree angle at the temporal fossa with the central point of the arc at the level of each frontozygomatic suture. The superior forehead component, about 1.0 to 1.5 cm up from the supraorbital rim, should have a gentle posterior curve of about 60 degrees and level out at the coronal suture region when seen in profile.

Orbito-Naso-Zygomatic Esthetic Unit

In the craniofacial dysostosis syndromes, the orbito-naso-zygomatic regional deformity is a reflection of the cranial base malformation. For example, in Crouzon syndrome, when bilateral coronal suture synostosis is combined with skull base and mid-facial deficiency, the orbito-naso-zygomatic region will be dysmorphic and consistent with a short (anteroposterior) and wide (transverse) anterior cranial base. In Apert syndrome, the nasal bones, orbits, and zygomas, like the anterior cranial base, are transversely wide and horizontally short (retruded), thereby resulting in a shallow hyperteloric upper mid-face (zygomas, orbits, and nose). Advancing the mid-face without simultaneously addressing the increased transverse width will not adequately correct the dysmorphology

Maxillary-Nasal Base Esthetic Unit

In a patient with craniofacial dysostosis and mid-face deficiency, the upper anterior portion of the face (nasion to maxillary incisor) is vertically short, and there is a lack of horizontal (anteroposterior) projection of the midface. These findings may be confirmed by cephalometric analysis, which indicates an SNA angle below the mean value and a short upper anterior facial height (nasion to anterior nasal spine). The width of the maxilla in the dentoalveolar region is generally constricted with a high arched palate. To normalize the maxillary-nasal base region, multidirectional surgical expansion and reshaping are generally required. The maxillary lip-to-tooth relationship and occlusion are normalized through Le Fort I osteotomy and orthodontic treatment as part of the staged reconstruction.

Morphologic Considerations

General

Examination of the patient’s entire craniofacial region should be meticulous and systematic. The skeleton and soft tissues are assessed in a standard fashion to identify all normal and abnormal anatomy. Specific findings tend to occur with particular malformations, but each patient is unique. Achievement of symmetry and normal proportions and reconstruction of specific esthetic units are essential to recreate an unobtrusive face in a child born with one of the craniofacial dysostosis syndromes.

Fronto-Forehead Esthetic Unit

The fronto-forehead region is dysmorphic in an infant with craniofacial dysostosis. Establishing normal position of the forehead is critical to achieve overall facial symmetry and balance. The forehead may be considered as two separate esthetic components: the supraorbital ridge–lateral orbital rim region and the superior forehead. The supraorbital ridge–lateral orbital rim region includes the glabella and supraorbital rim and extends inferiorly down each frontozygomatic suture toward the infraorbital rim and posteriorly along each temporoparietal region. The morphology and position of the supraorbital ridge–lateral orbital rim region are key elements of upper facial esthetics. In a normal forehead, at the level of the frontonasal suture an angle ranging from 90 to 110 degrees is formed by the supraorbital ridge and the nasal bones when viewed in profile. Additionally, the eyebrows, which overlie the supraorbital ridge, should be anterior to the cornea. When the supraorbital ridge is viewed from above, the rim should arc posteriorly to achieve a gentle 90-degree angle at the temporal fossa with the central point of the arc at the level of each frontozygomatic suture. The superior forehead component, about 1.0 to 1.5 cm up from the supraorbital rim, should have a gentle posterior curve of about 60 degrees and level out at the coronal suture region when seen in profile.

Orbito-Naso-Zygomatic Esthetic Unit

In the craniofacial dysostosis syndromes, the orbito-naso-zygomatic regional deformity is a reflection of the cranial base malformation. For example, in Crouzon syndrome, when bilateral coronal suture synostosis is combined with skull base and mid-facial deficiency, the orbito-naso-zygomatic region will be dysmorphic and consistent with a short (anteroposterior) and wide (transverse) anterior cranial base. In Apert syndrome, the nasal bones, orbits, and zygomas, like the anterior cranial base, are transversely wide and horizontally short (retruded), thereby resulting in a shallow hyperteloric upper mid-face (zygomas, orbits, and nose). Advancing the mid-face without simultaneously addressing the increased transverse width will not adequately correct the dysmorphology

Maxillary-Nasal Base Esthetic Unit

In a patient with craniofacial dysostosis and mid-face deficiency, the upper anterior portion of the face (nasion to maxillary incisor) is vertically short, and there is a lack of horizontal (anteroposterior) projection of the midface. These findings may be confirmed by cephalometric analysis, which indicates an SNA angle below the mean value and a short upper anterior facial height (nasion to anterior nasal spine). The width of the maxilla in the dentoalveolar region is generally constricted with a high arched palate. To normalize the maxillary-nasal base region, multidirectional surgical expansion and reshaping are generally required. The maxillary lip-to-tooth relationship and occlusion are normalized through Le Fort I osteotomy and orthodontic treatment as part of the staged reconstruction.

Surgical Management

General Considerations

Philosophy Regarding Timing of Intervention

In considering the timing and type of intervention, experienced surgeons will take several biologic realities into account: the natural course of the malformation (i.e., is the dysmorphology associated with progressively worsening Crouzon syndrome or is it a non-progressive craniofacial deformity?), the tendency toward restricted growth of an operated-on bone (esthetic unit) that has not yet reached maturity (i.e., we know that operating on the palate of a child born with a cleft in infancy will cause scarring and later result in maxillary hypoplasia in a significant percentage of individuals), and the uncertain relationship between the underlying growing viscera (i.e., brain or eyes) and the congenitally affected and surgically altered skeleton (i.e., if the cranial vault is not surgically decompressed/expanded by 1 year of life in a patient with a syndrome, will brain compression occur?).

In attempting to limit functional impairment and also achieve long-term ideal facial esthetics, an essential question that the surgeon must ask is, “ during the course of craniofacial development, does the operated-on facial skeleton of a child with craniofacial dysostosis tend to grow abnormally and result in further distortions and dysmorphology, or are the initial positive skeletal changes (achieved at surgery) maintained during ongoing growth? ” Unfortunately, the theory that craniofacial procedures carried out early in infancy will “unlock growth” has not been documented through the scientific method.

Management of Intracranial Dead Space

Management of dead space during cranial vault/cranial base expansion is critical to limit complications. Dead space within the cranial vault after cranial expansion at the time of reconstruction is managed by gentle handling of the tissues, achievement of good hemostasis, closure of tissue layers, placement of bone grafts, and obliteration (of dead space) with soft tissue flaps/grafts.

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Jun 4, 2016 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Craniofacial Dysostosis Syndromes
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