Aetiology of Herniation of the Hindbrain in Craniosynostosis

Abstract

The occurrence and extent of herniation of the hindbrain has been evaluated in a population of children with craniosynostosis by means of magnetic resonance imaging of the craniocervical junction. The role of intracranial pressure (ICP), posterior fossa size and hydrocephalus in the development of this deformity has also been assessed. Magnetic resonance imaging (Siemens Magnetom 1.5T) was reviewed in 27 cases of craniosynostosis in whom there had been no previous cranial vault surgery. The position of the cerebellar tonsils in relation to the plane of the foramen magnum was measured and an index of the size of the posterior fossa relative to the rest of the cranial vault was also calculated for each case. The presence of hydrocephalus (requiring a cerebrospinal fluid diversion procedure) was documented. In 22 of these cases overnight, subdural ICP monitoring using the Camino fibre optic device had also been performed. Herniation of the hindbrain below the plane of the foramen magnum occurred in 10 of 27 cases (37%). The level of ICP showed a significant correlation with the extent of hindbrain herniation (p < 0.001) as did small posterior fossa size (p = 0.0035). Hydrocephalus was present in 4 patients, all of whom had hindbrain herniation. The extent of hindbrain herniation did not correlate with age (p = 0.48). We propose that herniation of the hindbrain in craniosynostosis is a consequence of brain deformation occurring in response to the physical forces imposed by a combination of the anatomical deformity at the skull base and intracranial hypertension rather than a primary malformation of brain development as commonly supposed.

MR Venography in Children with Complex Craniosynostosis

“…The tonsillar herniation observed in patients with syndromic craniosynostosis has also been attributed to a normal-sized cerebellum in a hypoplastic posterior fossa further compromised by premature closure of the lambdoid suture [4, 6]. In our study, premature closure of the lambdoid suture was related to more severe degrees of venous outflow obstruction by MRV, suggesting the same forces causing premature closure of the lambdoid sutures may also affect the jugular foramen.…”

“…The intra-cranial manifestations of chronic mildly elevated venous pressures are not clear. Thompson et al [4]studied children with complex craniosynostosis using MR and subdural ICP monitoring and found a significant correlation between the presence of tonsillar herniation and increased ICP. Although Thompson et al [4]concluded venous hypertension was responsible for the raised ICP, venous pressures were not measured in that study.…”

“…Thompson et al [4]studied children with complex craniosynostosis using MR and subdural ICP monitoring and found a significant correlation between the presence of tonsillar herniation and increased ICP. Although Thompson et al [4]concluded venous hypertension was responsible for the raised ICP, venous pressures were not measured in that study. Lack of correlation between venous outflow obstruction and venous hypertension was reported by Cinalli who noted uni- or bilateral jugular foramen stenosis in 12/20 patients with Crouzon’s syndrome studied with catheter angiography [7].…”

“…The syndromic craniosynostoses are classified according to the pattern of sutural fusion and associated anomalies of viscera and extremities while the less common nonsyndromic forms lack specific coexistent malformations. Communicating hydrocephalus and tonsillar herniation, reported in both the syndromic and nonsyndromic forms of complex craniosynostosis, have been attributed by some investigators to jugular foramen stenosis and resultant chronic intracranial venous hypertension [3, 4, 5]. Associated lambdoid synostosis resulting in a constricted posterior fossa has also been implicated in progressive tonsillar herniation [6, 7].…”

Preliminary Observations on the Association between Simple Metopic Ridging in Children without Trigonocephaly and the Chiari I Malformation

“…The Chiari I malformation has been historically noted in patients with various forms of craniosynostosis [1, 2, 3, 4, 5, 6]. To our knowledge, metopic synostosis has not specifically been described as predisposing patients to cerebellar tonsillar ectopia.…”