The causes of cerebellar tonsil herniation (CTH) are very different and the clinical outcomes are varied. Congenital causes include hypoplasia of the posterior fossa, acquired causes include increased volume of the intracranial contents and abnormal intracranial pressure. CTH is not rare. Interpreting image characteristics and pathogenesis makes understanding clinical significance on each disorder with CTH. We propose to attend this objectifs: illustrate a summary of CTH. illustrate development of the skull related with CTH on embryologic aspect. present the concrete examples of some diseases associated...

1. What is the cerebellar tonsil herniation? Cerebellar tonsil herniation(CTH) is called as the tonsillar herniation, the downward cerebellar herniation and the transforaminal herniation. Depending on the degree of retraction, the degrees of symptoms also vary from none to serious. With wide foramen magnum or slowly progressive situation, it is only accompanied by slight symptoms or sometimes no symptoms. CTH may be accompanied by increased intracranial pressure and myelopathy associated with syringomyelia, may also require the decompression by the surgery. Due to retraction of the...

1) Chiari malformation(Fig.6) Hans Chiari as Austrian pathilogist in 1891 had divided Chiari malformation into four categories: Type I : more than 5mm of descent of only the cerebellar tonsil Type II : descent of the cerebellar tonsil, vermis, the fourth ventricle and medulla oblongata At present, type I and type II are classified by the absence or presence of myelomeningocele Type III : accompanied with the occipital meningocele Type IV : cerebellar hypoplasia At present, this is not included in the Chiari malformation Hydrocephalus...

CTH are very different and the clinical outcomes are varied. One of the congenital causes is hypoplasia of the posterior fossa. Mesodermal insufficiency induces Chiari malformation type I. Chiari malformation type II is induced by poor development of the primitive ventricle due to discharge of cerebrospinal fluid into the amniotic cavity. Synostosis of the lambdoid suture causes a shallow posterior fossa on craniosynostoses, for example Crouzon disease. Acquired causes include mass effect by tumors, intracranial hypertension, lumboperitoneal shunt, idiopathic and postoperative intracranial hypotension. Their mechanisms...

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