Authors

1. Doorenbosch, Xenia MBBS
2. Campbell, Jared BHsc(Hons), PhD
3. Umapathysivam, Kandiah PhD

Abstract

Review question/objective: The objective of this review is to identify the factors associated with an increased risk for developing recurrent raised intracranial pressure in nonsyndromic children who have had previous cranial vault remodelling surgery.

Background: An infant's skull is made up of several pairs of floating bone plates connected by fibrous tissues called sutures. The sutures allow for deformation during birth and expansion of the cranial vault in relation to brain volume growth. Brain growth pushes the two sides of the patent sutures apart, thereby enabling growth of the skull. The main sutures are named sagittal, metopic, coronal and lambdoid sutures. These sutures close at different ages by ossification; the metopic closes between three to nine months of age and the sagittal, lambdoid and coronal sutures close between 22 to 39 years of age.1

The term craniosynostosis was first described by Otto in 18302 and is defined as premature fusion of one or more cranial sutures which occur in isolation or in the context of a craniodystopic syndrome. It affects approximately one in 2000 births.3 There are several classifications of craniosynostosis; isolated or compound, primary or secondary and either syndromic or nonsyndromic.4 Isolated craniosynostosis refers to fusion of a single suture and compound refers to premature fusion of multiple cranial sutures. Syndromic synostosis typically involves premature fusion of multiple sutures and are hereditary forms of craniosynotosis with extracranial features which are associated with mutations of fibroblast growth factor receptor family (FGFR1, FGFR2, FGFR3), TWIST1 and MSX2 gene.1 The well known syndromes associated with craniosynostosis include Pfeiffer, Apert, Crouzon, Muenke and Saethre-Chotzen.4 Nonsyndromic craniosynostosis relates to sporadic cases without the presence of extracranial features. Primary craniosynostosis occurs in the absence of an associated syndrome or known cause, whereas secondary craniosynostosis refers to premature fusion secondary to a craniofacial syndrome or intracranial, metabolic, teratogenic or haematological causes.4

Sagittal synostosis is seen in 40-55% of nonsyndromic cases and is therefore the most commonly affected.4 The second most common is coronal synostosis seen in 20-25% of nonsyndromic cases, followed by metopic synostosis in 5-15%. Lambdoid suture synostosis is extremely rare and makes up less than 5% of nonsyndromic cases.4

Craniosynostosis causes a characteristic cranial deformity. Virchow's law dictates that when a suture fuses prematurely, growth of the skull is typically restricted perpendicular to the fused suture and enhanced in a plane parallel to it in an attempt to compensate to provide adequate space for the growing brain.5 This knowledge allows clinicians to diagnose which suture has prematurely fused based on the distinct morphologic characteristics of the affected infant's head shape. Craniosynostosis is commonly evident at birth and is usually diagnosed in the first few months of life commonly due to the characteristic cranial deformity. In some cases, the synostosis is already evident in the antenatal ultrasound. Previously, skull radiographs alone were adequate to diagnose a single suture craniosynostosis. This is no longer acceptable as the only radiographic investigation because it often does not allow for adequate visualisation of the entire suture and also some of the sutures may not have completely fused. A 3D computed tomography CT scan is regarded as the current gold standard in the diagnosis of craniosynostosis as it not only allows for clear visualisation of the suture patency but also to exclude any underlying or associated intracranial abnormalities.6 The 3D CT scan is also utilised in the preoperative stage to plan the extent of cranial vault remodelling required.

Craniosynostosis is also a potential source of neural dysfunction. The premature ossification of cranial sutures does not merely cause facial symmetry and a dysmorphic head shape, it most importantly can cause raised intracranial pressure which can lead to visual impairment, deafness and possibly cognitive impairment.7,8 There is considerable debate in the literature on whether neurodevelopmental impairment exist in patients with nonsyndromic, single suture craniosynostosis. It remains challenging to clarify this controversy because the battery of tests used to gauge neurodevelopmental status and assess function at a specific point in time in infancy have poor long term predictive value as they relate to neurologic function.9 Even though Renier et al10 found increased intracranial pressure ICP in up to one third of patients older than one year with craniosynostosis, attributing intracranial pressure to neurodevelopmental delay is challenging considering the absence of "normative" data on paediatric ICP. Therefore the interpretation of increased ICP in the absence of clinical symptoms remains dubious.11 Contemporary neuropsychologic tests have been developed to detect subtle learning disabilities and studies utilising these methods have demonstrated that patients with nonsyndromic craniosynostosis tend to have decreased processing speed and difficulty performing tasks involving learning or memory, visual-spatial planning and problem solving. Magge et al9 suggested that surgery before the age of six months may be beneficial to improve IQ and mathematical performance.

Currently, most experts agree that surgery should be performed before the age of 12 months to take advantage of the normal period of rapid brain growth which occurs in the first year of life to splint open and remodel the cranial vault.12,13 Some authors strongly support surgery within three to nine months but ideally before six months to prevent further progression of the deformity, neurodevelopmental delay and the potential of developing raised ICP.8,11

Despite significant advances in the management of craniosynostosis, surgical treatment remains the only treatment. There are many variations of surgical treatment performed and some are more extensive than others. Essentially, the goals of surgery include excising the fused suture, normalising the skull shape and expanding the cranial vault to allow for normal brain growth and prevent refusion as well as the potential sequelae of increased intracranial pressure.3 The literature remains divided whether or not a more extensive calvarial remodelling surgery as opposed to a limited suturectomy plays a role in the development recurrent raised ICP.

The rate of reoperation is an important outcome variable in the surgical treatment of craniosynostosis. Currently the literature reports a reoperation rate between 5-75%.14,15 However, only few papers distinguish between reoperation for aesthetic reasons or due to recurrent synostosis causing raised intracranial pressure.16 We aim to review specifically those risk factors associated with reoperation for recurrent synostosis causing raised intracranial pressure, as this is clinically more pertinent. Reoperation should not be taken lightly as it is associated with higher morbidity. In an older child, the skull is much thicker and does not lend itself to remodelling as easily as in infants. Additionally, the dura is often strongly adherent to areas of previous craniectomy and therefore more prone to tears and the risk of wound breakdown is higher in repeat surgery.

Many theories have been proposed as to why some children develop recurrent craniosynostosis associated with raised intracranial pressure following cranial vault remodelling surgery. These include involvement of more than one suture, patient's age at initial operation, stenosis of the coronal suture, the extent of the operation performed and whether the diagnosis of craniosynotosis was made antenatally or after birth.14-16 No previous systematic reviews have been performed on risk factors for reoperation for recurrent raised intracranial pressure.

The results of this review will inform clinical practice by helping surgeons minimise those modifiable factors which contribute to developing recurrent raised ICP in nonsyndromic children. When we are able to identify those factors associated with a higher probability of recurrent raised ICP, we may be able to minimise each patient's risk in order to prevent the need for a repeat operation with its associated morbidity. Additionally, we will be able to target those patients at higher risk with closer monitoring and investigations whilst concurrently reduce the frequency of outpatient reviews in those patients with a lower risk of developing recurrent raised ICP from restenosis. This will facilitate a more efficient use of the limited services available in the public health sector.