Mechanisms of cerebellar tonsil herniation in patients with Chiari malformations as guide to clinical management

Abstract

BackgroundThe pathogenesis of Chiari malformations is incompletely understood. We tested the hypothesis that different etiologies have different mechanisms of cerebellar tonsil herniation (CTH), as revealed by posterior cranial fossa (PCF) morphology.MethodsIn 741 patients with Chiari malformation type I (CM-I) and 11 patients with Chiari malformation type II (CM-II), the size of the occipital enchondrium and volume of the PCF (PCFV) were measured on reconstructed 2D-CT and MR images of the skull. Measurements were compared with those in 80 age- and sex-matched healthy control individuals, and the results were correlated with clinical findings.ResultsSignificant reductions of PCF size and volume were present in 388 patients with classical CM-I, 11 patients with CM-II, and five patients with CM-I and craniosynostosis. Occipital bone size and PCFV were normal in 225 patients with CM-I and occipitoatlantoaxial joint instability, 55 patients with CM-I and tethered cord syndrome (TCS), 30 patients with CM-I and intracranial mass lesions, and 28 patients with CM-I and lumboperitoneal shunts. Ten patients had miscellaneous etiologies. The size and area of the foramen magnum were significantly smaller in patients with classical CM-I and CM-I occurring with craniosynostosis and significantly larger in patients with CM-II and CM-I occurring with TCS.ConclusionsImportant clues concerning the pathogenesis of CTH were provided by morphometric measurements of the PCF. When these assessments were correlated with etiological factors, the following causal mechanisms were suggested: (1) cranial constriction; (2) cranial settling; (3) spinal cord tethering; (4) intracranial hypertension; and (5) intraspinal hypotension.

Management of Uncommon Secondary Trigeminal neuralgia related to a rare Arnold Chiari type I malformation

“…ACM is classified into four types. [9][10][11] Specifically, type 1 is characterized by herniation of cerebellar tonsils alone, radiologically as simple tonsillar herniation 5mm or greater, below the foramen magnum.…”

Chiari 1 Malformation and Holocord Syringomyelia in Hunter Syndrome

“…In the general population, CM1 is due to the underdevelopment of mesenchymal structures forming the clivus and posterior cranial fossa bones (Milhorat et al 2010). As MPS affect connective tissues with bone growth abnormalities (dysostosis multiplex), an increased rate of CM1 should not be completely unexpected.…”

“…CM1 is an uncommon condition (about 1 % in the pediatric population) (Aitken et al 2009) due to underdevelopment of mesenchymal structures forming the clivus and posterior cranial fossa bones (Milhorat et al 2010). The abnormal position of the cerebellar tonsils disrupts the normal CSF flow dynamics (Shah et al 2011) at the cranio-cervical junction and may result in spinal cord damage.…”

The Intracranial and Posterior Cranial Fossa Volumes and Volume Fractions in Children: A Stereological Study

“…When correlated with clinical findings, morphometric assessments of the PCF provide useful clues about the following mechanisms of cerebellar tonsil herniation (CTH): 1-cranial constriction; 2-spinal cord tethering; 3-cranial setting; 4-intracranial hypertension and 5-intraspinal hypotension. The differentialdiagnosis of CTH is likely to inform management strategies (Milhorat et al, 2010).…”