Multisutural syndromic synostosis

Chiari malformation

The Chiari I malformation is a downward displacement of the cerebellar tonsils through the foramen magnum and is present in up to 70% of patients with Crouzon syndrome, 82% with Pfeiffer syndrome, and 100% with the cloverleaf or Kleeblattshädel pattern of multiple suture synostosis. The malformation can result in noncommunicating hydrocephalus as a result of obstruction of cerebrospinal fluid outflow from the posterior fossa compression and can further progress to fluid accumulating within the spinal cord known as syringomyelia. Chiari malformation associated with syndromic synostosis has been considered an acquired condition developing in the first years of life secondary to hindbrain growth in an abnormally small posterior fossa from premature fusion of the lambdoid or cranial base sutures. However, a more recent study has suggested that posterior fossa volume is not predictive of Chiari malformations. Although a Chiari malformation can be suspected on a CT scan, the definitive imaging is a magnetic resonance (MR) scan that includes the upper spinal cord. Clinical symptoms if they do occur include headaches, dizziness, nausea, impaired coordination, muscle weakness, and in severe cases, paralysis.

Many patients with Chiari malformations remain asymptomatic and can be monitored with regular follow-up and repeat imaging for signs of deterioration. The recognized treatment of a symptomatic malformation is a bony decompression with a dura release and patch through a direct posterior neck approach by a neurosurgical team. The controversy over whether posterior fossa compression is the cause of the Chiari malformation adds to the debate whether prophylactic treatment of a non-symptomatic malformation through posterior vault expansion is warranted. Patients with Chiari malformations and craniosynostosis had similar posterior fossa volumes to patients with craniosynostosis alone. However, there have been a number of reports of resolution of a documented Chiari malformation with or without syringomyelia from an isolated posterior cranial vault expansion ( Fig. 25.3.6 ). Some centers advocate simultaneous removal of the posterior foramen magnum ring without dura release at time of posterior remodeling in high-risk cases. Our current approach is to perform this simultaneous bone decompression at the same time as a posterior vault distraction osteogenesis (PVDO) craniectomy in syndromic cases or cases with “Mercedes” (bilateral lambdoid with sagittal) synostosis with a documented Chiari malformation or CT evidence of regional bone invagination compressing the posterior fossa ( Fig. 25.3.7 ).

Management of cephalocranial disproportion in the first 2 years

There are several functional issues faced by patients with syndromic synostosis, and the timing of surgeries should be designed to reduce morbidity from intracranial pressure, airway compromise, exorbitism, and psychosocial development. Cranial vault expansion has been shown to acutely lower intracranial pressure, but patients with syndromic craniosynostosis have a high recurrence rate of intracranial hypertension. Timing of surgery to alleviate this pressure is critical, both acutely and longitudinally. Earlier cranial vault expansion can avoid increased intracranial pressure, while the calvaria is malleable and bony defects more readily heal. Later intervention allows more rigid fixation, which increases the predictability of surgery and the stability of the postoperative result. Utria et al . proposed that the timing of cranial vault remodeling was optimized around 6–9 months of age, with earlier operations having five times greater odds of requiring a major reoperation.

In severe cases of syndromic craniosynostosis, cephalocranial disproportion and iICP can be evident at birth, and staged interventions to relieve pressure on the intracranial contents must start in the first days or weeks of life. Left untreated, early cephalocranial disproportion in severe cases of syndromic synostosis will result in progressive loss of calvarial bone through compensatory over-expansion of patent minor sutures, such as the squamosal and frontozygomatic, as well as pressure erosion and thinning of the neonatal bone from the growing brain ( Fig. 25.3.8 ).

Early timely intervention to temporarily re-establish cephalocranial proportion will restore the balance between the brain, with its osteogenic dura, and the calvarium resulting in calvarial bone formation. Unfortunately, in the face of rapid brain growth in the first 2 years of life, the associated cerebrovascular, ventricular, and cranial suture abnormalities in syndromic synostosis make any early treatment a temporary fix, and disproportion and pressure will appear again, resulting in recurrent bone erosion and progressive decompensation. Timely detection of this recurrence of cephalocranial disproportion and staged treatment will reset the balance, restoring appropriate bone formation and cranial volume until the next occurrence of disproportion. We have coined this concept of ebb and flow of detecting cephalocranial disproportion and restoring balance through carefully time-staged surgical intervention in the first 2 years of life “surfing the bone pressure wave”. This wave can be represented by a graph of the amount of cranial bone surface area over time, and illustrates how the calvarial bone decreases in response to cephalocranial disproportion and iICP, but then increases in response to surgical interventions tailored to the patient’s age and situation ( Fig. 25.3.9 ). For example, if severe cephalocranial disproportion presents soon after birth in a patient with syndromic synostosis, surgical options are limited due to the fragility of the patient’s medical condition and cranium. A cranial strip release of the thickened bone band that forms from the sphenoid to the anterior fontanelle can stop progression of bone erosion and allow the brain to grow and deposit new bone. In a few months, the “wave” may rise again as the deposited bone fails to compensate from the rapidly growing brain that is compounded by early ventriculomegaly from hydrocephalus. The patient’s bone may still be too thin to allow a sustainable cranial expansion surgery, but a timely placed ventriculoperitoneal (VP) shunt in a patient with early signs of hydrocephalus can alleviate this pressure and temporarily restore the balance to allow bone formation to continue. In the second year of life, the imbalance may manifest again despite treatment of the hydrocephalus and frontal surgery is contraindicated due to the evidence of high relapse when performed at this age. However, sufficient bone has now formed for a craniectomy and placement of devices for posterior vault expansion from distraction osteogenesis. These early interventions have “surfed” bone pressure wave ebbs and flows into the second year of life, where a frontofacial procedure will have a more stable result in treating any residual disproportion and associated frontal abnormalities.

The rapid brain growth that achieves 90% of adult size in the first 2 years of life marks a critical period of surgical decision-making and tailored treatment. Adopting this “surfing the bone pressure wave concept” has resulted in patients historically thought to have extremely poor prognosis, such as the rare W290C variant of Pfeiffer syndrome, to achieve milestones that approach and, in some cases, exceed their age-matched non-synostotic peers. The next sections of this chapter focuses on specific surgeries that allow “surfing of the bone pressure wave”, two different approaches to detect or prevent cephalocranial disproportion, and a description of tailored sequences of craniofacial surgeries based on patient presentations.

Strip craniectomy

Neonatal strip craniectomy may be required in severe cases to stop early progressive cranial bone effacement due to iICP and cephalocranial disproportion following the “bone pressure wave” concept. Due to the higher risk of performing a craniectomy in the first month of life, this procedure should be reserved for the most severe phenotypes when other more conservative options are not available. Patients benefitting from neonatal strip craniectomy typically involve a combination of multiple suture synostosis, abnormal venous drainage, and are usually cases that eventually require shunting for hydrocephalus. Under these conditions, the expanding brain will compensate at the areas of lowest resistance, such as the squamosal and frontozygomatic suture as well as the anterior and posterior fontanelles but will be restricted by defined bony constriction bands from the pterion to the vertex. During neonatal strip craniectomy, these bands of thickened and constricting bone are identified and released to relieve temporarily the intracranial pressure and permit dural osteogenesis to occur ( Fig. 25.3.10 ). We perform neonatal strip craniectomy as an open procedure through the same coronal incision that will be used for future cranial surgeries. This allows direct visualization of the thinned and adherent dura but does result in increased blood loss and the need for transfusion.

Endoscopic strip craniectomy has been suggested as a surgical option in the first year for patients with syndromic craniosynostosis as a primary procedure. This differs from the indications for neonatal strip craniectomy for severe cephalocranial disproportion, but is instead proposed as an alternative to open procedures such as posterior expansion and fronto-orbital advancement. Proponents of endoscopic strip craniectomies report that it can slow or halt the progression of turricephaly, however, more than half of syndromic patients still require subsequent open anterior expansion. Isolated strip craniectomy in syndromic cases with bilateral coronal craniosynostosis relies on brain growth during helmet molding to correct the frontal bone dysmorphology. A direct comparison on morphometrics will be required to determine its relative efficacy in establishing nasofrontal relationship compared to open fronto-orbital advancement. Open or endoscopic strip craniectomy may not be a single stage solution for patients with syndromic craniosynostosis, but is believed to mitigate the effects of craniosynostosis in early infancy to delay subsequent posterior and anterior open corrections to a more appropriate age.

Posterior vault expansion

Historically, there has been debate on the efficacy of posterior versus anterior vault expansion as the first cranial procedure. The goals of early intervention are to enlarge the cranial volume to optimize brain growth and prevent any neurological complications of iICP. Proponents of anterior-first cranial expansion cite the importance of treating exorbitism with corneal protection provided by a fronto-orbital advancement (FOA). However, early frontal surgery has been recognized to have high relapse and reoperation rates. Proponents of posterior-first expansion, such as our team, note that it results in more than double the volume expansion compared to a fronto-orbital advancement ( Fig. 25.3.11 ) and results in less incidence of tonsillar herniation and papilloedema. Some techniques such as PVDO have also been associated with a decrease in the incidence of new Chiari malformations and improvement or resolution of existing Chiari malformations. Some centers are even examining posterior expansion as a first-line treatment in children with Chiari malformations. Early posterior expansion has been demonstrated to prevent the progression of turricephaly, improve frontal bossing, and further delay the need for a fronto-orbital advancement until an age when more stable results can be achieved. Overall, this staged approach of early posterior expansion followed by later anterior advancement may reduce the total number of transcranial surgeries that a child with severe syndromic craniosynostosis needs throughout their life. There are several techniques described for posterior cranial vault expansion, including open posterior cranial vault expansion, spring-assisted posterior vault expansion, and PVDO. It is important to note that not all syndromic patients require a posterior cranial expansion, and if a posterior-first approach is used, patients at risk of corneal ulceration from severe exorbitism will require a tarsorrhaphy until the second stage anterior expansion is performed. In an accepted but unpublished review, 23% of the Apert and Crouzon cases in the Seattle Children’s database and 35% at Great Ormond Street London underwent posterior vault expansion surgeries in the first 2 years of life.

Posterior vault distraction osteogenesis

Posterior vault distraction osteogenesis (PVDO) was first described using devices designed for mandible distraction osteogenesis to apply a gradual opening force across a circumferential cranial osteotomy. Although the same distraction protocol is followed as has been used for other facial bones, with a brief latency phase, followed by activation at 1 mm/day, and a prolonged consolidation phase, it is theorized that the bone that forms in the expanding cranial gap is not due to the undifferentiated bony regenerate tissue typically associated with distraction. Instead, the bone is likely regenerated when the pre-osteoblasts at the osteotomy interact with the FGF-2-rich environment created by the juvenile dura. Unlike open PVCE, in PVDO the osteotomy is limited to what is needed to create mobility of the posterior cranial transport segment so that the bone plate can remain attached to the underlying dura without the need to dissect over the torcula. Care must be taken to avoid injury to the transverse venous sinuses which can be invaginated between endocranial bone ridges ( Fig. 25.3.4B ). Similar to other forms of distraction osteogenesis, gradual controlled expansion is thought to maintain vascularity of the transported bone and prevent a sudden increase in dead space between the bone and brain. While one of the challenges of open PCVE is to achieve soft tissue closure over the expanded cranial volume, in PVDO, tension-free skin closure can be achieved since the expansion only occurs after surgery when the devices are activated. The devices also act as internal stabilizers of the opening osteotomies when the child is in the supine position. Unlike PVCE which can be modified to any cranial shape, PVDO provides a unidirectional expansion which cannot correct for multiple vectors of deformity.

The PVDO technique involves a circumferential osteotomy from the vertex, inferior to the squamosal suture, posterior above the petrous ridge, then inferior to the torcula as low as possible and continuing in a symmetric pattern on the contralateral side. No epidural dissection is performed except for that needed for the osteotomy. Paired internal distraction devices are then placed parallel to the desired direction of expansion, with detachable percutaneous activation arms extending either anteriorly or posteriorly ( Fig. 25.3.12 ). The most stable bone for mounting the devices is typically just superior to the squamosal suture. A third device can be placed parasagittal if there would otherwise be asymmetric expansion due to a patent lambdoid suture or instability of the bone flap. A systematic review of PVDO protocols reported that latency periods ranged between 1 to 7 days, with most undergoing a latency period of 5 to 7 days. Distraction rates ranged from 0.5 mm to 2 mm per day, with the majority distracting at 1 mm per day. The consolidation period ranged from 28 to 156 days, with most patients undergoing 2–3 months of consolidation.