CONGENITAL ANOMALIES AND PEDIATRIC PLASTIC SURGERY
CHAPTER 22 SINGLE-SUTURE CRANIOSYNOSTOSIS AND DEFORMATIONAL PLAGIOCEPHALY
GARY F. ROGERS AND STEPHEN M. WARREN
Craniosynostosis is the premature fusion of one or more cranial sutures. This pathologic process occurs in 1 in 2,000 to 2,500 live births and can occur in association with more than 130 different syndromes (multi-suture craniosynostosis is discussed in Chapter 23).1 Any cranial suture can ossify prematurely, but fusion is most common in the sagittal suture (40% to 55%), followed by the coronal (20% to 25%), metopic (5% to 15%), and lambdoid (1% to 5%) sutures. Craniosynostosis results in characteristic changes to the cranial shape that indicates which suture(s) is involved (Virchow’s law). Patients with craniosynostosis, especially syndromic forms, may also have other physical findings such as midface hypoplasia, deafness, blindness, speech impairments, learning disabilities, nasopharyngeal airway obstruction, swallowing dysfunction, heart and lung abnormalities, and extremity anomalies.
The diagnosis, management, and treatment of craniosynostosis can be complex and requires coordinated care. This is best accomplished by an interdisciplinary team comprised of professionals from the following disciplines: anesthesiology, craniofacial surgery, genetics, hand surgery, intensive care, neurosurgery, nursing, ophthalmology, orthodontics, pediatrics, pediatric dentistry, prosthodontics, psychology, radiology, social work, and speech/language pathology.2 Implicit in the choice of a team is the understanding that the first procedure provides the best opportunity for an optimal surgical outcome. A good or excellent surgical outcome is more challenging to achieve if critical tissues are surgically damaged, malpositioned, or discarded. An experienced team is even more important when contemplating surgical revision.
Historically, three etiopathogenic theories have dominated the field of craniosynostosis. In his 1851 paper on cretinism and pathologic brain malformation, Rudolph Virchow suggested that cranial suture fate was independent of the neurocranial environment. He presumed that the osteogenic fronts of the calvarial suture possessed the autonomous capacity (i.e., independent of interactions with the dura mater or brain) to fuse or remain patent. Virchow based his deductions on the work of Sommering (1800), who first described cranial suture anatomy and proposed that premature suture fusion could alter the head shape. Virchow’s etiopathogenic theory also benefitted from the work of Otto, who used Sommering’s observations to develop the hypothesis that suture fusion in one region on the cranium leads to compensatory overgrowth in another. Virchow’s primary contribution was to expand and refine Otto’s proposal and provided more conclusive support for what is now known as Virchow’s law: premature suture fusion results in compensatory skull growth parallel to the fused suture and a decreased growth perpendicular to the suture (Figure 22.1).
Virchow’s hypothesis of skull maldevelopment remained unchanged for nearly 70 years until 1920, when Park and Powers postulated that craniosynostosis was caused by a primary defect in the cranial suture mesenchymal blastema. They alleged that an embryologic defect in the cranial suture mesenchyme leads to premature fusion. Their theory was pervasive until Van der Klaauw (1946) and Moss (1959) suggested that the dura mater acted as a conduit or “functional matrix” for cranial base biomechanical forces. Accordingly, transmitted tension from an abnormal cranial base would presumably alter normal cranial suture physiology. For example, in coronal synostosis, spatially malformed lesser sphenoidal wings were hypothesized to transmit aberrant tensile force upward through dural fiber tracts leading to premature fusion of the overlying cranial suture. In sagittal synostosis, abnormalities in the cribriform plate and crista galli could generate forces that, at the points of dural attachment, would promote premature suture fusion.
Contemporary research has fundamentally changed our understanding of cranial suture fate. Based on a wealth of evidence, it appears that conserved signaling pathways mediate cranial suture fate. Numerous in vitro and in vivo models have demonstrated that the subjacent dura mater shapes the cranial suture complex by temporally and spatially supplying growth factors (e.g., fibroblast growth factor-2) and cellular elements (e.g., osteoblastic cells) to the overlying osteogenic fronts and suture mesenchyme. Genetic findings in human syndromic and nonsyndromic craniosynostoses indirectly support this hypothesis. Using positional cloning, candidate gene approaches, and comparative genomic hybridization techniques, over 100 mutations have been identified in genes such as TWIST, NELL-1, MSX2, GLI3, AND FGFR1-3.1 Exactly how these mutations cause craniosynostosis is still being elucidated.3 The link between cranial suture fusion and facial hypoplasia appears to occur through a secondary cascade of growth impairment that extends from the cranial base through the facial skeleton. Findings by Mooney and others suggest that the calvarial dysmorphology can drive the basicranial and midface changes. Further supporting evidence for the primacy of cranial vault pathology comes from clinical observations by Marsh, Vannier, and others that early cranial vault remodeling can sometimes lessen the severity of cranial base and facial abnormalities.
The sequelae of craniosynostosis include both physical deformity and insufficient cranial volume to permit normal brain growth and development. While the effects of synostosis on brain development are unclear, some studies demonstrate neurocognitive deficiencies in children with synostosis; the etiopathogenesis of these neurocognitive impairments, however, remains unknown and may be the result of, or simply associated with, the fusion of a cranial suture.
HISTORY OF TREATMENT
The work of Otto and Virchow on the role of the cranial sutures in normal and abnormal calvarial growth provided the basis for early operative treatment of craniosynostosis. The first recorded operations removed the offending suture in an attempt to release the constricted brain. In 1890, Lannelogue described bilateral strip craniectomies for the correction of craniosynostosis. Lane subsequently described a similar and successful procedure in a 9-month-old infant with microcephaly. Two years later, Jacobi reported poor outcomes and high morbidity and mortality in 33 patients with craniosynostosis treated with open strip craniectomy. He attributed these untoward consequences to major blood loss associated with the extensive surgical exposure. Interestingly, some authorities dispute whether many of these infants actually suffered from craniosynostosis and contend that some had microcephaly as a consequence of poor brain development. Either way, these “brain-releasing” procedures were abandoned in infants until 1927 when Faber and Town presented their successful experience using open craniectomy to treat severe forms of craniosynostosis in young infants. The success of these surgeons led to an acceptance of more extensive operative treatments that persist today.
FIGURE 22.1. Schematic drawing of metopic, sagittal, coronal, and lambdoidal cranial sutures. The confluence points of the cranial sutures form the anterior, posterior, anterolateral (sphenoid), and posterolateral (mastoid) fontanelles. The fontanelles close sequentially and the sutures function as growth centers. The metopic suture fuses by 8 months of age in nearly all children. The remaining sutures fuse late in life. Virchow’s law states that premature suture fusion results in compensatory skull growth parallel to the fused suture and a decreased growth perpendicular to the suture.
As anesthetic and blood management techniques improved, many surgeons became dissatisfied with the unpredictable results of simple suturectomy and began to use more extensive reshaping techniques. In 1967, Tessier presented his experience with cranial vault remodeling procedures that involved segmental bone removal, remodeling, and stabilization. The operations he described were much more extensive than the any previous methods; Tessier’s operations required more operative time, more blood loss, and observation in an intensive care unit. Nevertheless, because the bone segments were directly contoured and stabilized to achieve the desired shape, these operations generally had more predictable outcomes than simple release procedures. Furthermore, they could be done at any age since they did not rely on brain expansion to improve the cranial form or volume. These techniques remain the gold standard in most large craniofacial centers.
Recently, several less invasive methods to treat craniosynostosis have been introduced. In 1999, Jimenez and Barone presented their experience with endoscopic strip craniectomy and postoperative orthotic helmet therapy. The suturectomy was performed with the assistance of an endoscope through small incisions. The patients were fitted with a postoperative cranial orthosis to guide changes in cranial shape. The authors reported significant reductions in blood loss and transfusion, hospital stay, and cost compared with larger cranial vault remodeling procedures. Other authors have noted similar results.4 The effectiveness of this procedure, however, is limited to infants in the first several months of life and the outcomes of certain types of craniosynostosis, such as metopic, can be variable.2 In 2003, Lauritzen introduced the use of internal spring distractors to improve cranial shape.5 When compared with a modified pi procedure for sagittal synostosis, spring-mediated skull reshaping had comparable clinical outcomes with appreciably less morbidity. The application has been expanded to most forms of craniosynostosis with good reported outcomes.6 Since this procedure does not rely on the brain to expand the bone segments, it can be done successfully in older infants who would not be candidates for simple suturectomy.
The addition of three-dimensional computed tomography (CT), computer-guided modeling, improved pediatric anesthesia and blood conservation/salvage techniques, critical care, and intraoperative monitoring have improved the safety and effectiveness of craniofacial surgery and decreased the morbidity and mortality. Fixation using resorbable plates and screws has also greatly improved the stability and longevity of the correction. The adaptation of distraction osteogenesis to the craniofacial skeleton plays a small role in skull remodeling, but it has radically altered and expanded our surgical armamentarium for the treatment of midface hypoplasia in syndromic patients.
CRANIAL ANATOMY AND THE DEVELOPMENT OF ANOMALIES
The morphogenetic path between craniofacial embryogenesis and pathogenesis is extremely narrow. Cephalic development involves exceedingly complex mechanisms built on conserved elements that have undergone enormous evolutionary change. Cranial plates of the membranous neurocranium develop through the coalescence of ossification centers that arise from the primitive mesenchyme overlying the brain (membranous ossification). The majority of the cranial base, or chondrocranium, begins as a cartilaginous anlage that becomes ossified gradually during embryologic development (endochondral ossification). Cranial sutures and fontanelles are the mesenchyme that persists between the calvarial plates. The major cranial sutures are the metopic, sagittal, coronal, and lambdoid (Figure 22.1). A list of minor sutures includes the temporosquamosal, frontonasal, sphenoethmoidal, and frontosphenoidal.
The cranial sutures are important for two reasons. First, they allow the head to deform during parturition so that the infant can pass through the pelvis. Second, the sutures couple rapid brain expansion early in life to the growth of the cranium. Coordinated allometric growth of the cranium is achieved through a series of tissue interactions between the brain, dura mater, suture mesenchyme, and calvarial bones. Growth of the cranium is passive and occurs in response to outward expansion of the brain. This creates tension across the sutures and stimulates formation of new bone along the edge of the adjacent bony plates (osteogenic fronts of the cranial sutures). Thus, the cranial sutures permit the cranium to grow and expand as rapidly as the underlying brain.
Craniosynostosis can impair brain growth and development. Normally, the brain attains about 83% of its final volume by 2 years of age and the remaining 17% is acquired between 2 and 8 years of age.7 With the exception of the metopic suture, which normally closes by 8 months of age, the other cranial sutures are patent during this period.3 If a single suture fuses prematurely, compensatory growth in the remaining patent sutures will lead to alterations in cranial shape (as predicted by Virchow’s law) but rarely leads to significant neurologic impairment. Single-suture fusions are occasionally associated with elevated intracranial pressures (ICPs) (~7.7%) and subtle learning disabilities that go largely unrecognized.8 The most common single suture to fuse prematurely is the sagittal suture, followed by the coronal, metopic, and lambdoid. Although most patients with single-suture synostosis have no associated syndrome or identifiable genetic cause, approximately 25% of patients with unilateral coronal synostosis will have a causative mutation (FGFR3 Pro250Arg, FGFR2, TWIST, EFNB1, and NELL-1) and nearly 30% of patients with metopic synostosis have an associated syndrome or a chromosome abnormality.1 Furthermore, familiar patterns of inheritance have been observed in sagittal synostosis. Thus, it is inaccurate to use the terms nonsyndromic and syndromic craniosynostosis synonymously with single and multiple-suture craniosynostosis.
Multiple-suture fusions significantly raise the possibility of cerebral compression and developmental effects (see section on Increased Intracranial Pressure). The most common multiple-suture fusion is bilateral coronal, but other unusual patterns have been described. Multiple-suture fusion that occurs early in utero can result in a cloverleaf, or Kleeblattschädel, deformity. In rare instances, all of the cranial sutures can be patent at birth and fuse later in infancy, a process termed progressive postnatal pansynostosis. These infants have small, but normally shaped heads and the only clinic sign may be a relentless decline in head circumference percentile. Most patients with multiple-suture fusions have an associated syndrome and a molecular basis for their craniosynostosis. The most common mutation associated with bilateral (and unilateral) coronal synostosis is the FGFR3 Pro250Arg mutation (Muenke syndrome), followed by mutations in TWIST (Saethre-Chotzen syndrome), FGFR2 (Apert, Crouzon, and Pfeiffer syndromes), and EFNB1 (craniofrontonasal malformation). The incidence of developmental and neurocognitive problems in this group is much higher than is seen in patients with single-suture fusion. It is unclear if this observation is a result of the craniosynostosis, or the effect of the genetic aberration on brain development.
Increased Intracranial Pressure
It has long been observed that changes in calvarial shape can induce compensatory changes in the shape of the underlying brain. With premature fusion of the cranial sutures and continued brain growth, surgeons have long speculated that such a mismatch in shape and volume between the cranium and the brain could lead to elevated ICP and neuropsychosocial retardation. Lannelongue (1890) suggested that craniosynostosis resulted in microcephaly with secondary mental retardation. He thought that excision of the fused sutures could reverse or prevent intellectual impairment. Shillito and Matson also advocated craniectomy in infancy to prevent elevated ICP and subsequent brain damage. Marchac and Renier measured the ICP in 121 craniosynostosis patients with an epidural sensor.8 They detected elevated ICP in 42% of patients with multiple-suture involvement and in 7% to 13% of patients with single-suture involvement.8 They noted a decrease in ICP in patients who underwent cranial surgery.8Gault et al. also demonstrated that raised ICP was most frequent in those children with more than one suture fused prematurely (complex, oxycephaly, Crouzon, brachycephaly, and Apert syndromes).
Craniocerebral disproportion, however, is not the only cause of elevated ICP in patients with craniosynostosis. Sleep apnea resulting from midfacial retrusion can induce episodic nocturnal elevations in ICP secondary to the dilating effects of hypercapnia on the cerebral vasculature. Another potential cause is venous hypertension resulting from stenosis or complete closure of the sigmoid/jugular sinus complex.
The gold standard for detecting elevated ICP is direct monitoring. Intraparenchymal and intraventricular monitoring is more accurate than epidural measurements. The reliability of lumbar puncture is questionable. One difficulty in interpreting these numbers is that they fluctuate significantly with patient position, activity, blood pressure, and sleep. The most meaningful results are obtained when patients are monitored for a period of time, usually overnight. Significant elevations (>20 mm Hg) have been considered an absolute indication for intracranial expansion. Nevertheless, interpreting the significance of borderline pressure elevations (15 to 20 mm Hg) has been more problematic, and there is little consensus even among neurosurgeons.
Direct ICP monitoring is invasive and rarely used for routine screening. Moreover, the measurement is only a snapshot in time: a normal pressure measurement early in life does not imply that it will remain so as the brain continues to grow. Consequently, many surgeons resort to less invasive, but less reliable, indicators of ICP. Conventional clinical symptoms of acute ICP elevation, such as headache, somnolence, and dizziness, are often lacking even in affected children. Papilledema and subsequent optic atrophy is strongly suggestive of elevated ICP, but has limited sensitivity in children under 8 years of age. Findings can include blurring of the disk margins and obliteration of the optic cup, elevation of the nerve head (“champagne cork” appearance), capillary congestion, hyperemia, venous engorgement, loss of venous pulse, peripapillary exudates, retinal wrinkling, and punctate nerve fiber layer hemorrhages. As optic atrophy progresses, the disk becomes pale, the capillaries and hyperemia disappear, and significant secondary arteriolar narrowing occurs. Reducing ICP can reverse early changes, but more advanced degeneration may be permanent.
Radiographic evidence suggestive of elevated ICP includes loss of subdural space, often with effacement of the basal cisterns and vertex sulci, ventricular compression, and scalloping of the cranial endocortex. This latter finding has been termed the “copper-beaten” skull and can be visualized on both conventional radiography and CT. It is a late finding caused by pressure remodeling of the inner table of the skull by the gyral convolutions. The predictability of this finding for ICP elevation has been questioned. While CT is the standard imaging technique, new imaging modalities are on the horizon. For example, one day it may be possible to diagnose and monitor increased ICP using transcranial ultrasound and resistive index calculations to assess the peak systolic and diastolic velocities of the major cerebral vasculature (these velocities increase as ICP rises). Similarly, magnetic resonance elastography may also be used in the future to measure ICP.
Hydrocephalus is an infrequent finding in craniosynostosis. It is more common in patients with Crouzon syndrome. CT scans provide an accurate and noninvasive method of assessing ventricular size; however, assessment of ventricular size alone may not provide a true picture of hydrocephalus. For instance, ventriculomegaly is a common finding in patients with Apert syndrome, but is usually unrelated to increased ICP. More consistent findings include elevation of ICP on direct monitoring, the presence of enlarged or enlarging ventricles by serial CT scans, and periventricular lucency resulting from transependymal flow of cerebrospinal fluid (CSF).
Children with craniosynostosis can have cognitive delay and learning disability. However, intellectual development and learning are affected by many variables, including the presence of an associated syndrome, concurrent ICP elevation or hydrocephalus, prematurity, or family history. Patients with single-suture fusion and without an associated syndrome generally have near normal intelligence, but, as noted above, they may exhibit subtle learning disabilities. Patients with an associated syndrome have a significantly higher incidence of cognitive delay than the general population. This is loosely correlated with the type of syndromic diagnosis, but there is typically wide variability within any given patient population.
It is still unclear if the neurocognitive findings in patients with craniosynostosis are the result of the deleterious effects of early growth restriction from the suture fusions, or if the molecular process that lead to the suture fusion negatively impacted central nervous system development. In support of the former contention, Marchac and Renier found that overall intelligence was better in patients who underwent an earlier cranial release compared with those who had a later procedure.8 The findings are somewhat limited by the fact that the study was not controlled or randomized. Conversely, Starr and coworkers demonstrated that surgery did not favorably affect neurocognitve development in patients with single-suture synostosis.9 The parameter studied, however, was developmental quotient, not a sensitive indicator of intellectual performance and of questionable validity in younger age groups. Similarly, Camfield and Camfield concluded that mental impairment (IQ < 70) in children with single-suture craniosynostosis was usually the consequence of a primary brain malformation rather than brain distortion from the craniosynostosis. A major limitation of most prior neurocognitive studies in this patient population is that the instruments most commonly used (e.g., Bayley Scales and IQ testing) lack sufficient sensitivity and specificity to detect subtle cognitive differences, such as perceptual abnormalities. More refined testing is needed to provide a more global and comprehensive understanding of cognitive function in these patients.
Ocular anomalies are not uncommon in patients with craniosynostosis. Hypertelorism, exorbitism, strabismus, and proptosis are common with many syndromic forms of bilateral coronal synostosis. This is secondary to decreased orbital depth and widening of the ethmoidal air cells and can lead to corneal exposure and damage. Hypotelorism and strabismus can be associated with metopic synostosis. Patients with unilateral coronal synostosis have elevation of the lesser and greater sphenoid wings (harlequin deformity) that result in strabismus and ocular torticollis (head tilt to unfused side) in nearly 80% of affected patients. In addition, the contralateral orbital roof is depressed and 55% of patients have astigmatism. Patients with Saethre-Chotzen syndrome (TWIST mutation) demonstrate upper eyelid ptosis. Many of these manifestations are disfiguring and some can threaten vision. Patients with strabismus or nonconjugate vision can develop decreased vision from amblyopia ex anopsia if the visual axis disturbance is not corrected. Strabismus and amblyopia can occur in up to 40% of patients with syndromic craniosynostosis, but are less common in those without an associated syndrome. Patching of one eye and operative balancing of the extraocular muscles are the mainstays of treatment.
Patients with craniosynostosis require interdisciplinary care and, therefore, should be managed at a craniofacial center.2 Patients with syndromic craniosynostosis require the greatest scope and duration of care. Nevertheless, comprehensive assessment by an experienced craniofacial team is desirable even for patients with isolated single-suture fusion. Initial assessment involves a careful history and physical examination. Most surgeons can correctly identify which suture is fused based on the cranial shape. Furthermore, obvious phenotypic features, such as complex syndactyly, are usually not challenging to link to an associated syndrome, such as Apert syndrome. However, preoperative genetic testing and counseling are highly recommended to help confirm less obvious diagnoses and provide the family (and the craniofacial team) with important prognostic information. If possible, neuropsychological evaluation should be performed to assess developmental milestones. Syndromic patients with significant midfacial retrusion may demonstrate obstructive sleep apnea and have difficult airways. Pulmonary and otolaryngologic evaluation may include fiberoptic laryngoscopy and sleep studies. Early intervention in such infants may include continuous positive airway pressure. In selected patients, with severe midfacial deformities, tracheostomy may be required. Additionally, a careful audiologic assessment should be performed on any patient with an associated syndrome. Neurosensory abnormalities are present in 95% of patients with Muenke syndrome (FGFR3 Pro250Arg), and conductive hearing loss is common in Seathre-Chotzen syndrome, Apert syndrome, and Pfeiffer syndrome.
A psychologist may be helpful to provide support for the patient and family. Additional evaluations by the orthodontist, otolaryngologist, and ophthalmologist are critical in patients with syndromic craniosynostosis. For patients undergoing complex reconstructions, it is important to anticipate intraoperative and postoperative requirements. The role of the pediatric anesthesiologist and intensive care staff in this regard cannot be overstated, and every patient should undergo a preoperative evaluation by these specialists. Special attention should be focused on strategies to reduce blood loss and transfusion requirements, and the postoperative airway management.
CT is the most accurate radiographic method to confirm suspected craniosynostosis. Standard radiographs can be helpful in some instances (e.g., young infants), but they are a distant second choice if CT is available. CT scans allow the osseous anatomy, including the sutures, to be examined with exceptional detail. In most situations, CT scans are not necessary to make the diagnosis of craniosynostosis since the cranial shape is usually pathognomonic. However, minor forms of craniosynostosis (e.g., frontosphenoidal) or certain multiple-suture fusion patterns may require CT to define the pathology. The use of CT for diagnosis and follow-up of craniosynostosis has been questioned because of the risks associated with even minor amounts of ionizing radiation in infants. In addition, infants and young children may require sedation to obtain CT scan. While the adverse health effects of CT are still being debated, it is recommended that these tests should only be ordered if the information provided is essential for care of the patient. Both authors use CT scans only in selective cases.
Three-dimensional reconstruction of the cranium, orbits, and face is particularly useful to judge the Cartesian relationship between these structures (Figure 22.2). Computer-aided design and virtual surgery provide additional benefit for patients undergoing complex primary or secondary procedures. For example, computer-generated models can be manufactured and milled from three-dimensional CT data and used preoperatively to assist in planning osteotomies. Virtual simulations of preoperative osteotomies and bony movements are now becoming available.
Magnetic resonance imaging (MRI) is primarily used for soft tissue imaging and, therefore, is not routinely used for nonsyndromic craniosynostosis. In syndromic cases, it can help diagnose associated brain abnormalities (e.g., agenesis of the corpus callosum) or the presence of an Arnold-Chiari malformation. The latter diagnosis is particularly important to identify prior to using the modified prone position for total vault exposure during surgery. Cervical spine films should be taken in addition to the MRI to exclude the presence of craniovertebral anomalies or instability that might lead to spinal cord or brainstem injury during such positioning. Although MRI does not expose the patient to ionizing radiation, the test requires the patients to be motionless, and infants and young children often necessitate anesthesia. As with any test, the most important consideration when planning an imaging strategy is to have a clearly defined question and to select the imaging modality with the highest likelihood of safely providing the answer.
FIGURE 22.2. Axial (left) and three-dimensional (right) CT scan of a 5-month-old patient with metopic craniosynostosis (trigonocephaly). The metopic suture fusion is more accurately detected on the axial images because the volume averaging of a three-dimensional surface rendering can inadvertently make the suture appear fused. The three-dimensional surface rendering provides excellent spatial relationship of affected and unaffected structures. Note: the coronal and lambdoidal sutures are patent in the axial image. The coronal sutures can also be seen in the three-dimensional image.
Timing of Surgery
The optimal timing for surgical treatment of craniosynostosis is debatable. One philosophy is to operate as soon as possible to halt further progression of secondary craniofacial changes, allow normal brain expansion, and capitalize on the ameliorating effects of brain growth on overall skull shape. There is also a higher likelihood in a young infant that any bone defects created during the operation will spontaneously ossify. However, there is a higher risk of anesthetic-related complications in infants under a year of age, and some authors have observed a greater need for revision in patients who are undergoing open remodeling procedures before 6 months of age. The compromise between these considerations generally yields an operative age between 3 and 12 months of age, although this depends on many factors, including the operative technique employed, surgeon preference, and the risk of waiting.
A significant modifying factor for delaying surgery is the type of procedure, which will dictate the duration of surgery and the anticipated blood loss. Techniques that require minimal operative dissection and have limited bleeding, such as the pi procedure (for sagittal synostosis), endoscopic suturectomy, and spring-mediated distraction, are usually performed before 6 months of age. Suturectomy and, to a lesser degree, the pi procedure depend on brain growth to improve cranial shape and, therefore, are only effective if they are done at a very early age (2 to 5 months of age). Spring-mediated distraction does not rely on brain growth for correction and can be used effectively in older infants (7 to 8 months of age). Large open cranial remodeling procedures have significant blood loss (300 to 400 cc) and relatively long operative times (3 to 5 hours) and are often deferred for safety reasons until the infant is 8 to 12 months of age. Even this generality has exceptions. For example, an infant with multiple-suture fusions and clear clinical evidence of elevated ICP will require cranial release shortly after birth. Thus, the optimal time for operative intervention will depend on many variables and should be tailored to the needs of the patient.
Type of Surgery
There is considerable variation from one center to the next in terms of management of craniosynostosis. These variations include the use of endoscopic-assisted extended strip craniectomies with postoperative cranial orthosis, springs, distraction devices, and open partial or total cranial vault remodeling procedures. The choice of treatment depends on many factors, including, but not limited to, the patient’s age, the location and number of sutures fused, the presence of an associated syndrome, severity of pathology, and surgeon/center experience.
CLINICAL OBSERVATIONS AND MANAGEMENT
The metopic suture is the first cranial suture to fuse and the only one to fuse in childhood. It begins fusing as early as 3 months of age and is complete in nearly all patients by 6 to 8 months of age. Unlike the other cranial sutures, radiographic evidence of a fused metopic suture in infancy or early childhood is not per se abnormal. Instead, it is the phenotype (i.e., the extent of forehead and superior orbital narrowing) that defines whether a radiographically closed metopic suture is considered craniosynostosis (abnormally premature) or represents normal physiologic closure. There is wide variation in the degree of forehead deformity, and the line between normal and abnormal forehead contour is poorly defined. As a consequence, there can be significant diagnostic inconsistency between centers and surgeons. On the more severe end of the spectrum, premature closure of the metopic suture results in a “keel”-shaped deformity termed trigonocephaly (Figure 22.3). Other findings include small, flat frontal bones, anterior displacement of the coronal sutures, and compensatory enlargement of the parietal elements. The triangular cranial shape is exaggerated by the lack of lateral projection of the supraorbital rims and narrowing of the temporal regions (Figure 22.3). Patients often have hypotelorism, strabismus, and upslanting palpebral fissures (this is sometimes referred to as the trigonocephalic “sequence”).
FIGURE 22.3. Intraoperative superior view of a 9-month-old patient with metopic craniosynostosis (trigonocephaly) lying supine on the table. Zigzag (or straight) markings are made at about the level of the coronal sutures (left). After elevating the coronal flap, the frontal bones are small and flat (right). The coronal sutures are anteriorly displaced and there is compensatory enlargement of the parietal elements. The triangular cranial shape is exaggerated by the lack of lateral projection of the supraorbital rims and narrowing of the temporal regions.
Metopic synostosis has long been thought of as a relatively uncommon form of craniosynostosis accounting for only 5% to 15% of single-suture, nonsyndromic craniosynostoses. Recent publications and presentations suggest that the incidence of metopic synostosis has increased and is as high as 25%. Because there are no clear objective criteria for defining trigonocephaly, it is possible that the reported rise in this condition at some centers reflects a lower threshold for diagnosis rather than a true increase in prevalence. Brain expansion is not usually impaired by trigonocephaly, although Renier et al.8 noted elevated ICP in 7.7% of patients. However, it is important to note that 33% of patients with metopic synostosis have an associated syndromic diagnosis (e.g., Opitz C with agenesis of the corpus callosum) or chromosome abnormality. These patients may have inherent limitations to frontal lobe development, and forehead correction after surgery may deteriorate over time.
For infants less than 3 months of age, endoscopic suturectomy and postoperative cranial orthosis therapy are treatment options. However, the outcomes using this technique for metopic synostosis are the most unpredictable of all the single-suture synostoses, and the possibility of incomplete correction and need for a subsequent open remodeling procedure should be discussed with the family. Spring-mediated distraction is another alternative in children up to 7 months of age.5,6 This technique has also been shown to correct associated hypotelorism, a benefit that seems unique to this method.
In many centers, open fronto-orbital advancement is the preferred way of treating metopic synostosis. This method has predictably good outcomes if done correctly and, unlike the aforementioned techniques, can be used in older infants and children. This is performed with the patient in the supine position. The frontal bones and orbital bandeau are removed. A stair-step osteotomy is performed at the midline. This step does not correct the hypotelorism, but instead allows the bandeau to be widened in the temporal areas. The V-shaped bandeau is expanded and, if necessary, the flat lateral segments are contoured to increase the convexity. In severe cases, the expanded bandeau may require a midline separation and leveling of each half. If this creates a gap, it can be filled with a trapezoidal or triangular bone graft. The nasal process of each frontal bone is long and should be shortened. The bandeau is intentionally overcorrected in the temporal areas and fixed with resorbable plates. The coronal gap can be filled with a rectangular piece of bone harvested from the vertex to stabilize the bandeau, provide bony continuity, and prevent any possibility of collapse. While the frontal elements are off, particulate bone graft can be harvested from the inner table and stored in a blood-filled container on the back table. This will provide bone graft to repair any defects created by the advancement or harvest of full-thickness bone graft. Each frontal bone is then remodeled with a shaping burr and/or radial osteotomies and then orthotopically or heterotopically affixed to the bandeau. The bifrontoparietal segments can be affixed to the bandeau with resorbable plates, secured with wires or sutures. In order to create a smooth transition with the widened frontal segments, the parietal bones laterally should be outfractured using horizontal barrel staves and stabilized to the frontal elements with absorbable plates. Although the lateral bone gaps between the frontal and parietal segments could be left to heal spontaneously, repair with full-thickness cortical bone harvested from the vertex provides bone continuity and reduces the likelihood of a depression (temporal hollow) in this area. Any bony gaps on the vertex can be filled with particulate graft stabilized with fibrin glue.10 As a last step, some surgeons (e.g., GFR) believe that the temporalis muscle should be advanced anteriorly because the fronto-orbital advancement procedure obligatorily moves the anterior boundary of the temporal fossa forward. Surgeons who perform this procedure feel that failure to advance and re-suspend the temporalis muscle to help fill this void can increase the likelihood of temporal hollowing, a significant problem following these corrections. Whether the surgeon performs a temporalis muscle advancement or not if the soft tissue closure is tight, the galea can be scored to reduce tension on the repair. If this is done carefully, this will not induce alopecia.
In older children, the bony remodeling techniques are altered to allow reshaping of the more mature cranial vault. The bone may be more brittle and bending is difficult. The major difference in technique in this age group involves selective weakening of the bone by the placement of endocortical channels or “kerfs” in the bone. Patients older than 1 year of age usually require bone grafting of osseous defects remaining after correction. The harvest of autogenous bone graft from the endocortical surface of the frontal bones simultaneously weakens the bone and provides a plentiful source of autogenous bone graft. Since there is less opportunity for bony remodeling in older patients, accurate contouring and positioning of all bone segments is critical.
Unilateral Coronal Synostosis
Premature fusion of one of the coronal sutures, or synostotic frontal plagiocephaly (a Greek term meaning oblique skull), is the second most common type of craniosynostosis (20% to 25%) and occurs in approximately 1 in 10,000 live births. Fusion of the coronal suture impairs ventral expansion of the anterior cranial fossa and leads to shortening of the anterior cranial fossa ipsilateral to the fused suture. Growth superiorly results in elongation of the forehead, whereas inferiorly directed growth produces deformity of the middle cranial fossa with ventral bowing of the greater wing of the sphenoid. The deformity of the sphenoid results in effacement of the temporal fossa, which, combined with shortening of the lateral wall of the orbit, produces mild proptosis of the globe. The “harlequin” orbit seen on anterior–posterior radiographs is pathognomonic for unilateral coronal synostosis and is secondary to the lack of descent of the greater wing of the sphenoid during development. There is a compensatory bulge in the ipsilateral squamous portion of the temporal bone, contralateral frontal and parietal bones, and, to a much lesser degree, the contralateral occipital bone. The fused coronal suture may demonstrate prominent ridging, and the ipsilateral frontal and parietal bones are flattened.
The facial features associated with unilateral coronal craniosynostosis are quite predictable. There is shortening of the ipsilateral palpebral fissure, superior and posterior displacement of the ipsilateral orbital rim and eyebrow, and deviation of the nasal root toward the flattened frontal bone. The chin point deviates to the contralateral side, and the malar eminence is displaced anteriorly on the fused side. As noted above, the orbital changes cause ocular torticollis in approximately 80% of patients and nearly half have astigmatism on the side opposite the fusion. Twenty-five percent of patients have an associated molecular/syndromic diagnosis, the most common being FGFR3 Pro250Arg (Muenke syndrome), followed by FGFR2, TWIST (Saethre-Chotzen syndrome), and EFNB1 (craniofrontonasal malformation).
Endoscopic suturectomy and postoperative helmet therapy and spring-mediated distraction are options for early correction of unilateral coronal synostosis. One study found a lower incidence of ocular torticollis and astigmatism in patients undergoing early endoscopic suturectomy compared with those who had a later fronto-orbital advancement. In addition, early intervention may lead to better overall facial symmetry. The results of these techniques are promising but further validation of the long-term outcomes is still not available. Most centers still treat coronal craniosynostosis using conventional fronto-orbital advancement. The patient is placed supine and a bifrontal craniotomy is performed (Figure 22.4). The orbital bandeau is removed and recontoured, often with an intentional anterior overcorrection on the ipsilateral side. The affected side must be overcorrected or reversion to the pathologic asymmetry is assured. Some authors have recommended using an onlay bone graft over the orbital rim on the ipsilateral side to help accentuate the sagittal projection. The bandeau is orthotopically repositioned with an ipsilateral advancement and affixed to the temporal fossa with a resorbable plate. Some patients with associated syndromic diagnoses can have relative retrusion on the unfused side as well and may require an asymmetric bilateral advancement to create adequate projection of the orbital rims and forehead. With large advancements, a full-thickness rectangular bone graft behind the bandeau will help prevent postoperative collapse and ensure bony healing. Some surgeons choose to perform dural plication with the bipolar cautery or with sutures to correct the contralateral prominence of the dura. The frontal bone is remodeled using radial osteotomies, and selective fractures are performed to achieve the desired form. The convexity of the ipsilateral bone is increased while that of the contralateral side is decreased. The frontal bone plates are reattached to the orbital bandeau with sutures or wires. The frontal bones should be attached to the parietal segments to prevent collapse during redraping of the coronal flaps. Full-thickness bone grafts harvested from the vertex can be used to fill the lateral coronal gap, especially on the more advanced side. Particulate cranial bone graft harvested from the endocortex of the frontal elements, or ectocortex of the parietal bones, can easily cover all remaining bone defects. The asymmetry of the palpebral fissure can be corrected with a lateral canthopexy on the side of the fusion.
FIGURE 22.4. Intraoperative superior view of a 10-month-old patient with right coronal craniosynostosis (unilateral synostotic plagiocephaly) lying supine on the table. After elevating the coronal flap, the right frontal bone appears smaller and flatter (upper left). The orbital bandeau and frontal bones are removed and reshaped on the back table (upper right). Particulate bone can be harvested from the endocranial side of the frontal bones (lower left). The bandeau is orthotopically repositioned and secured with resorbable plates (lower right). The frontal bones can be orthotopically or heterotopically (pictured here) and the particulate bone graft can be used to fill the bone defects.
The sagittal suture is the most likely to fuse prematurely and comprises 40% to 55% of all forms of craniosynostosis. The male-to-female incidence ratio is 4:1. As the sagittal suture fuses, the expanding brain drives the coronal and lambdoid sutures to compensate by increasing bone deposition in the frontal and occipital bones, respectively. The metopic suture compensates with symmetric bone expansion along its borders. The compensatory growth process produces the characteristic frontal and occipital prominence seen in sagittal synostosis. The resultant cranium has an increased anteroposterior length and decreased width, yielding a “boatlike” or scaphocephalic shape. There is phenotypic variation depending on the timing and, for incomplete fusions, the extent and location of the suture closure.
As with other types of single-suture synostosis, endoscopic suturectomy and postoperative cranial orthosis therapy, or spring-mediated distraction can be used successfully in infants younger than 5 months of age. Correction of sagittal synostosis with either of these methods has been demonstrated to be highly effective and the likelihood of incomplete correction is remote. Endoscopic suturectomy is usually performed via one or two small (<2 cm) incisions placed perpendicular on either end of the sagittal suture. The fused sagittal suture is removed in a 1-cm strip of bone (Figure 22.5); some surgeons add temporal and parietal barrel stave osteotomies. Most surgeons recommend a postoperative cranial orthosis to help limit anterior–posterior growth and encourage bitemporal/biparietal expansion. There is little question that a properly designed and rigorously worn orthotic can significantly improve outcomes. The duration of wear is typically 6 to 10 months or until the desired shape is obtained. If patient compliance is unlikely or impractical, this option should not be used.
FIGURE 22.5. Comparison of endoscopic suturectomy and open cranial vault reshaping. Intraoperative superior view of a 3-month-old patient with sagittal craniosynostosis (scaphocephaly) lying in a modified prone position on the table (upper left). The endoscopic suturectomy is performed via two small (<2 cm) incisions placed perpendicular to the anterior and posterior limits of the sagittal suture. The fused sagittal suture is removed in a 1-cm strip of bone; some surgeons add temporal and parietal barrel stave osteotomies (upper right). Most surgeons recommend a postoperative cranial orthosis to help limit anterior–posterior growth and encourage bitemporal/biparietal expansion (middle left). The duration of wear is typically 6 to 10 months or until the desired shape is obtained. Alternatively, in older patients, sagittal craniosynostosis can be corrected with an open approach using a pi or modified pi procedure (middle right). The patient is typically placed in a modified prone position. The excised segments include bone on either side of the sagittal suture (which comprise the vertical limbs of the π) and a transverse segment of bone parallel to the coronal suture (which comprises the horizontal limb of the π) from squamosal suture to squamosal suture. Barrel stave osteotomies can be added as necessary to allow temporal/parietal outfracture. The “hung-span” modification of the pi procedure holds these barrel staves in position with a spanning resorbable plate extending from the frontal bone to the occipital bone along the equator of the skull (lower left). The anterior–posterior dimension of the cranium can be reduced by advancing the sagittal strip to the frontal bone and securing it with suture or resorbable plates. The degree of shortening that can be safely achieved is variable and limited by the shape of the underlying brain. However, aggressive shorting is not recommended.
Spring-mediated distraction does not rely on brain growth to expand and correct the cranial shape and can be used in infants up to 7 to 8 months with very good results. Suturectomy can be done through an open vertex incision or small incisions (similar to those described above) with endoscopic assistance. A sagittal strip of bone is removed and two properly tensioned springs are positioned between the edges of the bone gap. This technique requires a second minor operation to remove the springs, although this can be done through small incisions and minor blood loss. A postoperative helmet is not required.
In addition to these options, some surgeons use a pi or modified pi procedure (named after its semblance to the Greek letter π) in affected infants who are less than 6 months of age. This operation is midway between an open remodeling and a suturectomy and has acceptable outcomes. It is simple to perform and is commonly used. The patient is typically placed in the modified prone position. The excised segments include bone on either side of the sagittal suture (which comprise the vertical limbs of the π) and a transverse segment of bone parallel to the coronal suture (which comprises the horizontal limb of the π) from squamosal suture to squamosal suture (Figure 22.5). Barrel stave osteotomies can be added as necessary to allow temporal/parietal outfracture. The “hung-span” modification of the pi procedure holds these barrel staves in position with a spanning resorbable plate extending from the frontal bone to the occipital bone along the equator of the skull. The anterior–posterior dimension of the cranium can be reduced by advancing the sagittal strip to the frontal bone and securing it with suture or resorbable plates. The degree of shortening that can be safely done is variable and limited by the shape of the underlying brain. However, aggressive shorting is not recommended.
For patients who present later (>6 months), the cranial bones are less malleable and more predictable outcomes can be obtained with subtotal or total calvarial remodeling. The primary operative goals are to release the stenosis and reshape the cranial vault by increasing the parietal and temporal width while gently decreasing its anteroposterior dimension. In an older child, the degree of anterior–posterior shortening that is safe is considerably less than in a young infant. Total vault remodeling for sagittal synostosis requires exposure from the glabella anteriorly to the posterior lip of the foramen magnum posteriorly. This can be achieved using a modified prone position. However, supine positioning on a cerebellar head holder can be just as effective and less risky. The supine position for correction of sagittal synostosis requires some head manipulation to access the posterior cranium and it is wise to secure the endotracheal tube to the mandible or dentition prior to prepping. An awl can be used to pass a 26-gauge wire around the mandible; for patients with mature dentition, the wire can be affixed to the teeth. The frontal and parietal segments are removed. Low temporal and parietal regions’ barrel stave osteotomies are performed and the segments are outfractured. This greatly expands the parietal width and provides a more complete release. The cone-shaped occiput is remodeled with radial osteotomies and bending to provide a more gradual convex curvature. The bifrontal fragment is radial osteotomized and similarly reshaped. Shortening of the anteroposterior length is not always required. However, this can be accomplished by resecting a portion of the frontal and parietal bones at the midline. The remaining parietal bone fragments are remodeled with the goal of increasing the lateral convexity, particularly in the parietal regions.
Once the bone fragments are remodeled satisfactorily, they are secured with wire, suture, or plates. In an older child, one of us (SMW) continues to use resorbable plates, while the other (GFR) will, on occasion, choose titanium plates because the risk of intracranial migration is minimal. The frontal segment is secured anteriorly to the superior orbital rims. If the occipital segment was removed, it is reattached to the basal occiput posteriorly. One of us (SMW) secures the parietal segments using a spanning resorbable plate (hung-span technique) from the frontal to the occipital segments. The other (GFR) secures the inferior aspect of each parietal bone is to the outfractured temporal bone with suture or wire. The parietal segments are then tilted laterally and affixed to the intact sagittal strip in an expanded position with resorbable plates. Additional stability can be obtained by affixing the parietal segments to the frontal and occipital bones with one long plate or several smaller segmental plates. Plate stabilization assures that the expansion and shape correction achieved intraoperatively will not relapse or collapse postoperatively.
In older children, the techniques of bone remodeling require several modifications. Kerfs, or channels, placed on the internal surface of the bone oriented perpendicular to the long axis of the bone segment, allow for selective weakening of the bone and easier reshaping and molding.
Lambdoid synostosis is the least common form of craniosynostosis (1% to 5%). It is characterized by ipsilateral occipital flattening, posterior/inferior displacement of the ispilateral ear, bossing of the ipsilateral mastoid, and decreased height of the cranial vertex on the affected side. These features usually allow the surgeon to readily distinguish lambdoid synostosis from the more common cause of posterior cranial flattening, deformational plagiocephaly, in which the ipsilateral ear and forehead are anteriorly displaced (Figure 22.6). The physical features of deformational plagiocephaly will be discussed in detail in the next section. In addition to differences in physical presentation, CT scan demonstrates bony bridging of the lambdoid suture and angulation of the posterior cranial fossa toward the side of the fusion. These findings are not present in deformational plagiocephaly. The distinction between deformational plagiocephaly and lambdoid synostosis is important since the former diagnosis rarely (if ever) warrants operative intervention, while the latter condition has traditionally been managed with surgery. The decision to recommend an operative repair for unilateral lambdoid synostosis depends on the severity of the deformity. The treatment varies depending on whether the condition is unilateral or bilateral, but the operative exposure and craniotomy lines are similar.
FIGURE 22.6. Intraoperative posterior view of a patient with left lambdoid craniosynostosis in the modified prone position (upper left). Left and right parieto-occipital bone grafts are outlined leaving a strip of bone over the sagittal suture (upper right). Barrel stave osteotomies are performed bilaterally in the flattened basal occipital bone to increase the convex projection of the occipital bone locally. The bilateral parieto-occipital bone grafts are cut radially and remodeled to achieve a normally rounded, symmetric posterior skull (lower left). The dura may be plicated in areas of excess projection before bone remodeling. The bone grafts may be orthotopically or heterotopically repositioned (pictured here) and secured with resorbable plates (lower right).
Operative Procedure. The patient is placed in the modified prone position and the occipital bone is fully visualized to the level of the foramen magnum. A bilateral parieto-occipital bone segment is elevated or each parieto-occipital bone graft can be elevated leaving a strip of bone over the sagittal suture (Figure 22.6). Barrel stave osteotomies are performed bilaterally in the flattened basal occipital bone to increase the convex projection of the occipital bone locally. In patients with moderate unilateral deformity, the barrel staves are placed primarily ipsilateral to the fused suture in the occipital bone. In more severe cases, bilateral barrel staves are performed to infracture the contralateral and outfracture the ipsilateral inferior occipital bone. The bilateral parieto-occipital bone grafts are cut radially and remodeled to achieve a normally rounded, symmetric posterior skull (Figure 22.6). The dura may be plicated in areas of excess projection before bone remodeling. The bone grafts may be orthotopically or heterotopically (switched) repositioned and secured with resorbable plates.
Complications are relatively infrequent and may be divided into those that are acute and those that are late.11 Acute complications include major blood loss, air embolus, dural tear with CSF leak, infection, and respiratory complications. Blood loss occurs nearly continuously intraoperatively and is the direct or indirect cause of most complications. Consequently, vigilant attention to accurate blood replacement is paramount to avoid coagulopathy secondary to dilution of clotting agents. Hemodynamically significant bleeding can occur with inadvertent tearing of a venous sinus or major cortical vein. Abnormal transosseous veins, especially in the region of the torcula, can occur and are at risk during posterior bone dissection. If a major vein is breached, blood loss can be rapid and life threatening. It is critical to have sufficient intravenous access to allow rapid resuscitation if needed. Blood loss may continue for 12 to 24 hours following cranial remodeling procedures, and intensive care unit monitoring is essential. Air embolus has been documented in children undergoing cranial procedures and may occur in any operative position, including supine. It is appropriate to consider the placement of precordial Doppler monitors and end-tidal CO2 monitors to ascertain entrainment of air into the venous system. Central venous lines are sometimes warranted to assess blood volume (and resuscitation) and can be helpful to evacuate an air embolus if it occurs.
Dural tears are not uncommon and should be identified and repaired acutely. An unrepaired or incompletely repaired dural tear can result in a persistent CSF leak into the drain (if one is used) or an unresolved fluid collection under the closed coronal flaps. The first intervention to treat a postoperative CSF leak is to decrease the outflow using a lumbar drain. If the output persists, surgical exploration and closure are required. Persistent CSF leak can lead to infection, thinning of the overlying bone, and a cranial defect. Infection is an uncommon problem after cranial procedures but in the rare instance it occurs; it can be potentially life threatening. Infection can arise from a persistent CSF leak or a communication of the intracranial cavity with the nasal cavity or frontal sinus. Because the frontal sinus develops quite late in childhood, the latter is seen as a consequence of surgery in the older child or adolescent.
Late complications are generally associated with the sequelae of abnormal bone healing and impaired bone growth. Children older than 1 year of age have a decreased ability to ossify cranial defects compared with younger patients. The rate of incomplete ossification has been estimated between 5% and 20% and is positively correlated with age at repair. Generally, defects greater than 2 cm at the end of a cranial procedure in children older than age 1 year should be repaired with split calvarial bone grafts or particulate bone graft to prevent postoperative cranial defects (see Chapter 31). Significant bone loss requiring bone grafting may occur in the setting of infection and subsequent resorption.
From its inception, the use of miniplate and microplate fixation has greatly improved the outcomes of craniofacial procedures. Early plating systems were made of titanium, but these plates and screws were noted to “migrate” intracranially when used in infants. Although no harmful effects were reported, most surgeons use resorbable plate fixation in the young child (<2 years of age) when it is feasible.
Relapse and recrudescence of the original cranial deformity are uncommon if the correction is performed and stabilized properly. However, numerous authors have reported partial relapse with growth even in single-suture synostoses. This may be a result of several factors. Correction of the neurocranium in infancy does not assure subsequent normal growth of calvaria and cranial base. Furthermore, any molecular effects that lead to the initial fusion in utero could still affect cranial growth until it is complete. Several studies have reported a negative correlation between age at repair and recurrence. The degree of relapse may also depend on the severity of the initial phenotype as well as the continued effect of cranial base restriction. More important factors may be incomplete correction or inadequate bone stabilization. Often, no matter what technique is performed, patients may appear slightly undercorrected in long-term follow-up. Some surgeons prefer allowing the bone segments to “float” in anticipation that brain growth will help “normalize” cranial shape. Unfortunately, this supposition has not been proven. Brain growth can be unpredictable in some patients and may not be sufficient to alter shape. In addition, the soft tissue envelope after a cranial expansion procedure is tight and can cause collapse of inadequately stabilized bone segments. It is much more predictable to achieve the desired correction before leaving the operating room. Cranial distraction has been advocated to reduce relapse by distracting the soft tissue and the bone simultaneously; however, these objectives can be more easily achieved using judicious release of the galea and particulate bone graft.
Overall, the morbidity and mortality from the treatment of craniosynostosis is quite low. Mortality has been variously reported to range between 1.5% and 2%. In 1979, Whitaker and coworkers reported the experience of six craniofacial centers and found a mortality rate of 1.6%. Current advances in monitoring and anesthetic techniques, as well as refinements in surgical techniques, have driven this rate well below 1% at most large centers.
DEFORMATIONAL PLAGIOCEPHALY AND BRACHYCEPHALY
In 1992, the American Academy of Pediatrics initiated the “Back to Sleep Campaign” to reduce the incidence of sudden infant death syndrome. This policy has been widely implemented and resulted in a 40% reduction in the incidence of sudden infant death syndrome in the United States. One of the unforeseen consequences of the campaign was a rise in asymmetric (plagiocephaly) and symmetric (brachycephaly) occipital flattening. Recent studies estimate the prevalence of deformational posterior cranial flattening to be as high as 20% in healthy infants; these estimates, of course, depend on how abnormal flattening is defined.
Deformational flattening can be asymmetric or symmetric.12,13 Asymmetric flattening is termed plagiocephaly, a word derived from the Greek derivatives “plagios” (oblique) and “kephale” (head). Symmetric flattening is termed brachycephaly, or “short head,” to denote the loss of cranial length with a compensatory increase in width. In reality, most patients have a combination of asymmetry and cranial shortening, termed asymmetric brachycephaly. Unlike craniosynostosis, deformational changes are thought to arise predominantly in the postnatal period in response to external resistance to the growing infant cranium. Many risk factors have been linked to the development of deformational flattening: supine sleep position, multiple births, developmental delay, small maternal pelvis, breech position, oligohydramnios, male sex of fetus, gestational diabetes, nulliparity of mother, high birth weight, large neonatal head size, vaginal delivery, prolonged length of post delivery, hospital stay (>4 days), and prolonged duration of stage II labor.14 While the variables in this list appear oddly unrelated, most of them can be placed into one of three major risk categories for cranial flattening: torticollis and cervical imbalance, prematurity, or developmental delay. They all share a common pathogenic link: each can directly or indirectly have a negative impact on infant head mobility early in life. If the infant is unable to alter his head position and redistribute the area of resistance, cranial growth will occur around the point of contact (usually the flat bed). This is analogous to how an unturned pumpkin flattens in a field—it cannot grow through the ground so it grows along the ground. Over time, compensatory and redirected growth will result in progressive flattening.
It has been suggested that supine positioning is the cause of flattening. However, it cannot be solely responsible since only 20% of supine infants develop flattening and these cranial changes are also observed in prone-slept infants, albeit to a lesser extent. There are two primary reasons why supine positioning results in more cases of clinically apparent flattening. First, the occipital cortex grows at a faster rate than the frontal cortex early in infancy. Thus, the degree of cranial deformity that can develop over a fixed period of time will be greater in a supine versus a prone-positioned infant and a greater percentage of supine-positioned infants will reach the severity threshold to be considered clinically flat. Second, supine infants reach early motor milestones slower than prone infants. Although the trend dissipates by a year of age, this means that supine infants will be slower to acquire independent head mobility (the antidote for flattening) than their prone-positioned counterparts.
Deformational plagiocephaly occurs primarily in infants with congenital muscular torticollis. This is not always easy to detect in a newborn, but the presence of a “preferred” head position early in life is highly suggestive. The resultant cranial shape has been compared with a “parallelogram”; however, the frontal bossing is usually never as significant as the occipital flattening. Asymmetric growth of the head is often accompanied by facial asymmetry, specifically an anterior shift of the ipsilateral forehead, ear, and cheek. Asymmetric opening of the palpebral fissures can also be observed as a consequence of the sagittal displacement of the ipsilateral zygoma. As asymmetric occipital flattening progresses, forward movement of the zygoma and attached lateral canthus on the affected side effectively shortens the distance between the medial and lateral canthal tendons. As a result, tension is reduced on the tarsal plates, and the eye appears more open on the side of the flattening. The vertical palpebral asymmetry can be easily confused with contralateral eyelid ptosis. As mentioned above, deformational plagiocephaly is usually readily distinguishable from posterior synostotic plagiocephaly by its combination of occipital flatness, ipsilateral anterior ear shear, and forehead bossing.
Deformational brachycephaly presents as relatively symmetrical occipital flattening and compensatory parietal widening. These infants have little or no occipital rounding and appear to have a disproportionately wide or “big” head viewed from the front. The posterior vertex may appear taller than the front, giving a sloped appearance to the head in profile.
Growth of the brain tends to improve symmetry of the craniofacial skeleton once the external point of resistance is removed. Since most patients develop good rotational control of the head by 3 to 4 months, it is unusual for flattening to progress after this time. The exceptions are infants with developmental delay or those who were significantly premature. Recognizing that supine positioning contributes to deformational plagiocephaly , primary care providers have educated parents about the importance of supervised prone positioning and alternating head position from left to right during supine sleep. In cases where muscular torticollis can be identified, physical therapy to stretch the sternocleidomastoid and trapezius muscles is prescribed. Infants are monitored on a monthly basis for signs of improvement. Those children who present early with mild or moderate deformity and signs of improvement can often be treated with positional therapy alone. More severely affected children may benefit from a cranial orthosis. Although an association between deformational flattening and developmental delay has been noted, it is the latter diagnosis that leads to the former, not vice versa.There is no convincing evidence that deformational flattening causes impairment of cognitive development, visual development, or temporomandibular joint function.
Deformational flattening is the most common cause of a cranial shape abnormality in an infant. By comparison, craniosynostosis is relatively rare. There are no functional implications from deformational flattening, and treatment is nonoperative. In contrast, patients with single-suture craniosynostosis can have low rates of elevated ICP, ocular abnormalities, and abnormalities in neurocognitive development. Therefore, it is imperative to properly distinguish these two entities in a timely fashion to ensure proper treatment. Early identification of craniosynostosis permits treatment with newer minimally invasive techniques. Open cranial reconstruction remains the standard for older infants; the complication rate is very low when performed by an experienced team at a state-of-the-art facility.
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