Restricted Brain Growth and Intracranial Pressure

If the rapid brain growth that normally occurs during infancy is to proceed unhindered, the cranial vault and skull base sutures must expand during phases of rapid growth, resulting in marginal ossification. In craniosynostosis, premature fusion of the suture(s) causes limited and abnormal skeletal expansion in the presence of continued brain growth. Depending on the number and location of prematurely fused sutures, the growth of the brain may be restricted. If surgical release of the affected suture(s) and reshaping of the involved skeleton to restore a more normal intracranial volume and configuration are not performed, decreased cognitive and behavioral function is likely to be the result.

Increased intracranial pressure (ICP) is the most serious functional problem associated with premature suture fusion. Radiographic findings that may suggest an increased ICP include the beaten-copper appearance along the inner table of the cranial vault seen on a plain radiograph or the loss of brain cisternae as observed on a computed tomographic (CT) scan. Although suggestive of increased ICP, these are considered soft findings.

Increased ICP is most likely to affect patients with great disparity between brain growth and intracranial capacity and is believed to occur in as many as 42% of untreated children in whom 2 or more sutures are affected. There is no agreement on what levels of ICP are normal at any given age in infancy and early childhood.

The clinical signs and symptoms related to increased ICP may have a slow onset and be difficult to recognize in the pediatric population. Although standardized CT scans allow for indirect measurement of intracranial volume, it is not yet possible to use these studies to make judgments as to who requires craniotomy for brain decompression. Comprehensive neurologic and ophthalmologic evaluation are critical components of the data gathering required to formulate definitive treatment plans in patients with one of the craniofacial dysostosis syndromes.

Vision

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

Some forms of craniofacial dysostosis (eg, Apert syndrome) result in a degree of orbital hypertelorism, which may compromise visual acuity and restrict binocular vision. Divergent or convergent nonparalytic strabismus or exotropia occurs frequently and should be considered during the diagnostic evaluation. This condition may be the result of congenital anomalies of the extraocular muscles themselves.

Hydrocephalus

Hydrocephalus affects as many as 10% of patients with a craniofacial dysostosis syndrome. The risk of intracranial hypertension is greatest in Crouzon syndrome. Even if every medical complication is managed promptly, a proportion of affected children develop congnitive delay and neurologic problems. Although the cause is often not clear, hydrocephalus may be secondary to a generalized cranial base stenosis with constriction of all the cranial base foramina, which affects the patient’s cerebral venous drainage and cerebrospinal fluid (CSF) flow dynamics. Hydrocephalus may be identified with the help of a CT scan or magnetic resonance imaging to document progressively enlarging ventricles. Difficulty exists in interpreting ventricular findings as seen on a CT scan especially when the skull and cranial base are brachycephalic. The skeletal dysmorphology seen in a child with cranial dysmorphology related to craniosynostosis (eg, bicoronal synostosis) may translate into an abnormal ventricular shape that is not necessarily related to abnormal CSF flow. Serial imaging with clinical correlation and experienced neurologic judgment is required in making these assessments.

Effects of Midface Deficiency on Airway

All newborn infants are obligate nasal breathers. Many infants born with a craniofacial dysostosis syndrome have moderate to severe hypoplasia of the midface as a component of their malformation. They have diminished nasal and nasopharyngeal spaces, with resulting increased nasal airway resistance (obstruction). The affected child is thus forced to breath 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. The neonate with severe midface hypoplasia experiences diminished nasal airflow and is 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 (eg, Apert syndrome), and enlarged tonsils and adenoids. The 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 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 central, obstructive, or mixed 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 specific situations, early midface advancement may be performed to improve the airway, allowing for tracheostomy decannulation. Central apnea may occur from poorly treated intracranial hypertension as well as other contributing factors. If so, the condition may improve by reducing the ICP through brain decompression. This goal is accomplished with cranioorbital or posterior cranial vault expansion.

Dentition and Occlusion

The incidence of dental and oral anomalies is higher among children with craniofacial dysostosis syndromes than within 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. Delayed dental eruption should also be expected. Confusion has arisen about whether the oral malformations and absence of teeth that are often characteristic of these conditions are a result of congenital or iatrogenic factors (eg, injury to dental follicles associated with early midface surgery). The midfacial hypoplasia seen in the craniofacial dysostosis syndromes often results in limited maxillary alveolar bone to house a full compliment of teeth. The result is severe crowding, which often requires serial extractions to address it. An Angle class III skeletal relationship in combination with anterior open bite deformity is typical.

Hearing

Hearing deficits are more common among patients with the craniofacial dysostosis syndromes than among the general population. In Crouzon syndrome, conductive hearing deficits are common, and atresia of the external auditory canals may also occur. Otitis media is more common in Apert syndrome, although the exact incidence is unknown. Middle ear disease may be related to the presence of a cleft palate that results in dysfunction of the eustachian tube. Congenital fixation of the stapedial footplate is also believed to be a frequent finding. The possibility of significant hearing loss is paramount and should not be overlooked because of preoccupation with other more easily appreciated craniofacial findings.

Restricted Brain Growth and Intracranial Pressure

If the rapid brain growth that normally occurs during infancy is to proceed unhindered, the cranial vault and skull base sutures must expand during phases of rapid growth, resulting in marginal ossification. In craniosynostosis, premature fusion of the suture(s) causes limited and abnormal skeletal expansion in the presence of continued brain growth. Depending on the number and location of prematurely fused sutures, the growth of the brain may be restricted. If surgical release of the affected suture(s) and reshaping of the involved skeleton to restore a more normal intracranial volume and configuration are not performed, decreased cognitive and behavioral function is likely to be the result.

Increased intracranial pressure (ICP) is the most serious functional problem associated with premature suture fusion. Radiographic findings that may suggest an increased ICP include the beaten-copper appearance along the inner table of the cranial vault seen on a plain radiograph or the loss of brain cisternae as observed on a computed tomographic (CT) scan. Although suggestive of increased ICP, these are considered soft findings.

Increased ICP is most likely to affect patients with great disparity between brain growth and intracranial capacity and is believed to occur in as many as 42% of untreated children in whom 2 or more sutures are affected. There is no agreement on what levels of ICP are normal at any given age in infancy and early childhood.

The clinical signs and symptoms related to increased ICP may have a slow onset and be difficult to recognize in the pediatric population. Although standardized CT scans allow for indirect measurement of intracranial volume, it is not yet possible to use these studies to make judgments as to who requires craniotomy for brain decompression. Comprehensive neurologic and ophthalmologic evaluation are critical components of the data gathering required to formulate definitive treatment plans in patients with one of the craniofacial dysostosis syndromes.

Vision

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

Some forms of craniofacial dysostosis (eg, Apert syndrome) result in a degree of orbital hypertelorism, which may compromise visual acuity and restrict binocular vision. Divergent or convergent nonparalytic strabismus or exotropia occurs frequently and should be considered during the diagnostic evaluation. This condition may be the result of congenital anomalies of the extraocular muscles themselves.

Hydrocephalus

Hydrocephalus affects as many as 10% of patients with a craniofacial dysostosis syndrome. The risk of intracranial hypertension is greatest in Crouzon syndrome. Even if every medical complication is managed promptly, a proportion of affected children develop congnitive delay and neurologic problems. Although the cause is often not clear, hydrocephalus may be secondary to a generalized cranial base stenosis with constriction of all the cranial base foramina, which affects the patient’s cerebral venous drainage and cerebrospinal fluid (CSF) flow dynamics. Hydrocephalus may be identified with the help of a CT scan or magnetic resonance imaging to document progressively enlarging ventricles. Difficulty exists in interpreting ventricular findings as seen on a CT scan especially when the skull and cranial base are brachycephalic. The skeletal dysmorphology seen in a child with cranial dysmorphology related to craniosynostosis (eg, bicoronal synostosis) may translate into an abnormal ventricular shape that is not necessarily related to abnormal CSF flow. Serial imaging with clinical correlation and experienced neurologic judgment is required in making these assessments.

Effects of Midface Deficiency on Airway

All newborn infants are obligate nasal breathers. Many infants born with a craniofacial dysostosis syndrome have moderate to severe hypoplasia of the midface as a component of their malformation. They have diminished nasal and nasopharyngeal spaces, with resulting increased nasal airway resistance (obstruction). The affected child is thus forced to breath 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. The neonate with severe midface hypoplasia experiences diminished nasal airflow and is 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 (eg, Apert syndrome), and enlarged tonsils and adenoids. The 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 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 central, obstructive, or mixed 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 specific situations, early midface advancement may be performed to improve the airway, allowing for tracheostomy decannulation. Central apnea may occur from poorly treated intracranial hypertension as well as other contributing factors. If so, the condition may improve by reducing the ICP through brain decompression. This goal is accomplished with cranioorbital or posterior cranial vault expansion.

Dentition and Occlusion

The incidence of dental and oral anomalies is higher among children with craniofacial dysostosis syndromes than within 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. Delayed dental eruption should also be expected. Confusion has arisen about whether the oral malformations and absence of teeth that are often characteristic of these conditions are a result of congenital or iatrogenic factors (eg, injury to dental follicles associated with early midface surgery). The midfacial hypoplasia seen in the craniofacial dysostosis syndromes often results in limited maxillary alveolar bone to house a full compliment of teeth. The result is severe crowding, which often requires serial extractions to address it. An Angle class III skeletal relationship in combination with anterior open bite deformity is typical.

Hearing

Hearing deficits are more common among patients with the craniofacial dysostosis syndromes than among the general population. In Crouzon syndrome, conductive hearing deficits are common, and atresia of the external auditory canals may also occur. Otitis media is more common in Apert syndrome, although the exact incidence is unknown. Middle ear disease may be related to the presence of a cleft palate that results in dysfunction of the eustachian tube. Congenital fixation of the stapedial footplate is also believed to be a frequent finding. The possibility of significant hearing loss is paramount and should not be overlooked because of preoccupation with other more easily appreciated craniofacial findings.

General

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

Frontoforehead Aesthetic Unit

The frontoforehead region is dysmorphic in an infant with craniofacial dysostosis. Establishing the normal position of the forehead is critical to overall facial symmetry and balance. The forehead may be considered as 2 separate aesthetic components: the supraorbital ridge-lateral orbital rim region and the superior forehead. The supraorbital ridge-lateral orbital rim region includes the nasofrontal process and supraorbital rim extending inferiorly down each frontozygomatic suture toward the infraorbital rim and posteriorly along each temporoparietal region. The shape and position of the supraorbital ridge-lateral orbital rim region are a key element of upper facial aesthetics. In a normal forehead, at the level of the nasofrontal suture, an angle ranging from 90° degrees to 110° is formed by the supraorbital ridge and the nasal bones when viewed in profile. In addition, the eyebrows, overlying 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° angle at the temporal fossa with a center 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°, leveling out at the coronal suture region when seen in profile.

Posterior Cranial Vault Aesthetic Unit

Symmetry, form, and adequate intracranial volume of the posterior cranial vault are closely linked. Posterior cranial vault flattening may result from either a unilateral or bilateral lambdoidal synostosis, which is rare, previous craniectomy with reossification in a dysmorphic flat shape, which is frequent, or postural molding because of repetitive supine sleep positioning. A short anterior-posterior cephalic length may be misinterpreted as an anterior cranial vault (forehead) problem when the occipitoparietal (posterior) skull represents the primary region of the deformity. Careful examination of the entire cranial vault is essential to defining the dysmorphic region so that when indicated appropriate cranial vault expansion may be performed.

Orbitonasozygomatic Aesthetic Unit

In the craniofacial dysostosis syndromes, the orbitonasozygomatic 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 midfacial deficiency, the orbitonasozygomatic region is dysmorphic and consistent with a short (anterior-posterior) and wide (transverse) anterior cranial base. In Apert syndrome, the nasal bones, orbits, and zygomas, like the anterior cranial base, are transversely wide from anterolateral bulging of the temporal lobes of the brain and horizontally short (retruded), resulting in a shallow hyperteloric reverse curved upper midface (zygomas, orbits, and nose). Surgically advancing the midface without simultaneously addressing the increased transverse width and reverse curve does not adequately correct the dysmorphology.

Maxillary-nasal Base Aesthetic Unit

In the patient with craniofacial dysostosis with midface deficiency, the upper anterior face is vertically short (nasion to maxillary incisor), and there is a lack of horizontal (anterior-posterior) projection of the midface. These findings may be confirmed through cephalometric analysis that 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 abnormal maxillary lip-to-tooth relationship and occlusion are improved through Le Fort I segmental osteotomies and orthodontic treatment as part of the staged reconstruction. The mandible and chin are frequently secondarily deformed and benefit from surgical repositioning as part of the orthognathic correction.

General Considerations

Philosophy regarding timing of intervention

In considering the timing and type of intervention the experienced surgeon should take several biologic realities into account: the natural course of the malformation (ie, is the dysmorphology associated with Crouzon syndrome progressively worsening or only a nonprogressive craniofacial deformity?); the tendency toward growth restriction of operated bones (aesthetic units) that have not yet reached maturity (ie, we know that operating on a cleft palate in infancy causes scarring and later results in maxillary hypoplasia in many individuals); and the relationship between the underlying growing viscera (ie, brain or eyes) and the congenitally affected and surgically altered skeleton (ie, in Crouzon syndrome if the cranial vault is not surgically expanded to decompress the brain by 1 year of life is brain compression likely to occur?).

In attempting to limit impairment and also achieve long-term preferred facial aesthetics and head and neck function an essential question the surgeon must ask is, “During the course of craniofacial development, does the operated-on facial skeleton of the child with craniofacial dysostosis tend to grow abnormally, resulting in further distortions and dysmorphology, or are the initial positive skeletal changes achieved (at operation) maintained during ongoing growth?” The proposed theory that craniofacial procedures performed early in infancy unlock growth has not been documented through the scientific method.

Incision placement

For exposure of the craniofacial skeleton above the Le Fort I level, the approach used is the coronal (skin) incision. This approach allows for a camouflaged access to the anterior and posterior cranial vault, orbits, nasal dorsum, zygomas, upper maxilla, pterygoid fossa, and temporomandibular joints. For added cosmetic advantage, placement of the coronal incision more posteriorly on the scalp and with postauricular rather than preauricular extensions is useful. When exposure of the maxilla at the Le Fort I level is required, a circumvestibular maxillary intraoral incision is used. Unless complications occur that warrant unusual exposure, no other incisions are required for managing any aspect of the reconstruction of the patient with craniofacial dysostosis. These incisions (coronal [scalp] and maxillary [circumvestibular]) may be reopened as needed to further complete the individual’s staged reconstruction.

Management of the cranial fossa dead space and communication across the skull base after total midface advancement

Cranial reshaping in the patient with craniofacial dysostosis provides space for the compressed brain to expand into. After anterior cranial vault expansion and monobloc advancement an immediate extradural (retrofrontal) dead space is combined with the gap created by osteotomy across the skull base (connecting the anterior cranial fossa and the nasal cavity). This combination of factors may complicate the postoperative recovery (eg, CSF leakage, infection, bone loss, fistula formation). After frontofacial advancement the nasal cavity-cranial fossa communication is managed by being gentle to the tissues; good hemostasis; effective repair of any dural tears (dural grafting as needed); complete separation of dural and nasal mucosal tissue planes by interposing a combination of bone grafts, tissue sealants, and flaps; avoidance of pressure gradients across the opening while the nasal mucosa is healing; and prevention of over- or undershunting (when a shunt is in place).

The preferred way to manage the retrofrontal (lobes of the brain) dead space and the gap across the skull base osteotomy site (separating the cranial fossa and nasal cavities) after frontofacial advancement remains controversial but it is a critical aspect of the reconstruction.

In the patient with craniofacial dysostosis rapid filling of the surgically expanded intracranial volume (6–8 weeks) by the previously compressed frontal lobes of the brain has been documented after cranioorbital expansion in infants. It has also been shown to occur after frontofacial advancement in children and young adults when the volume increase remains in a physiologic range. These observations support the conservative management of the retrofrontal dead space in younger patients. More gradual and less complete filling of the space is believed to occur in older children and adults. If so, this process may be particularly troublesome when the anterior cranial fossa dead space communicates directly with the nasal cavity (ie, monobloc advancement, facial bipartition, intracranial Le Fort III) across the (open-gap) skull base interface. When feasible, closing off (sealing) the nasal cavity from the cranial fossa across the skull base osteotomy at the time of operation is preferred. Insertion of a pericranial flap or other fillers can help to separate the cavities. The use of fibrin glue to seal the anterior cranial base provides a temporary separation between the cavities, allowing time for the reepithelialization (healing) of the torn nasal mucosa. To reconstruct the defect across the skull base (gap) bone grafts of various types may also be used. Until the torn nasal mucosa heals, potential communication between the nasal cavity and cranial fossa may result in the transfer of air, fluid, bacteria, and nasocranial fistula formation. To facilitate nasal mucosa healing and limit a pressure gradient across the communication, postoperative endotracheal intubation may be extended for 3 to 5 days and/or bilateral nasopharyngeal airways may be placed after extubation. The avoidance of positive pressure ventilation, enforcement of sinus precautions, and restriction of nose blowing further limit reflux of air, fluid, and bacteria (nose to cranial fossa) during the early postoperative period. When anterior cranial vault procedures are performed and aerated frontal sinuses are present, management is by either cranialization or obliteration.

Aside from a learning curve in mastering the technical skills of completing the monobloc osteotomies and disimpaction, the surgical morbidity from these procedures primarily results from a combination of the anticipated retrofrontal dead space, unavoidable tears in the nasal mucosa, and management of nasocranial communication across the skull base gap with the potential for fluid, air, and bacteria contamination.

The achievement of a normal occlusion is rarely a treatment objective at the time of monobloc advancement. Accomplishing an ideal occlusion without creating enophthalmus requires a separate Le Fort I osteotomy to differentially advance the maxilla, often combined with maxillary segmentation and mandibular (sagittal split) osteotomies. To achieve the most favorable facial balance for the patient with craniofacial dysostosis an experienced clinician’s aesthetic sense of the preferred morphology and focused technical expertise to alter the skeleton intraoperatively are essential. Several key technical aspects include:

• The ability to remove, segment, and then reshape and stabilize (plates and screws) the anterior cranial vault

• The ability to separate the orbits and midface as a unit (monobloc) from the skull base

• The ability to further segment the monobloc (at the upper orbits) and reconstruct (with cranial grafts) as needed.

• The ability to separate the monobloc into halves (facial bipartition) and then alter the 2 facial halves to achieve the most favorable morphology; this process often requires simultaneously increasing the maxillary transverse width and decreasing the upper face width to correct hypertelorism of the orbits, zygomas, nose, and bitemporal regions (eg, Apert syndrome); facial bipartition also provides the ability to correct transverse facial arc-of-rotation deformities (eg changing the Apert syndrome patient’s concave facial arc of rotation toward a normal convexity is an essential aspect of the reconstruction)

Any potential advantage of limiting morbidity caused by infection across the skull base with the distraction osteogenesis (DO) technique should be considered in light of limitations to achieve the key technical and aesthetic aspects mentioned earlier. Added morbidity with the DO technique caused by pin tract infection/scarring/loosening requiring reapplication, the need for device removal, and dependence on a patient’s, family’s, and clinician’s continued commitment to staying the course for necessary outpatient DO procedures/adjustments to achieve an acceptable result must also be factored into the decision-making process.

When a patient with craniofacial dysostosis is to undergo intracranial volume expansion as part of the craniofacial procedure and they also require hydrocephalus management, the potential for morbidity increases. Complications may arise from excessive CSF drainage (overshunting). With overshunting there is decreased brain volume to fill any surgically created retrofrontal dead space. Frontofacial advancement and/or cranial vault expansion procedures should be carefully staged with ventriculoperitoneal (VP) shunting procedures. We believe that the presence or absence of a VP shunt is not in itself a major risk factor in the success of a frontofacial advancement procedure. An important aspect is satisfactory physiologic function of the ventricular system. The decision regarding the need for and sequencing of shunting is based on the patient’s neurologic findings and the neurosurgeon’s judgment. In a patient with a VP shunt in place before the surgery, experienced neurosurgical evaluation, including CT scanning of the ventricular system, is performed to confirm physiologic shunt function.

Soft-tissue management

A layered closure of the coronal (scalp) incision (galea and skin) optimizes healing and limits scar widening. Resuspension of the midface periosteum to the temporalis fascia may facilitate redraping of the soft tissues. Each lateral canthus should be reattached in a superior-posterior direction to the newly repositioned lateral orbital rim. The use of chromic gut on the skin in children may be used to obviate postoperative suture or staple removal.