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We just reviewed a number of cases

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of posterior fossa abnormalities.

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Some of them have similarities,

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some of them have differences.

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Hopefully, after reviewing these cases,

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you can better appreciate the

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similarities and the differences

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and the clinical implications of some.

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For Chiari I malformations,

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there are mild and moderate

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and severe malformations,

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and the measurement of the

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cerebellar tonsils below the plane

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of the foramen magnum is probably

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not the most important abnormality.

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Chiari II malformations have a variety

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of both posterior fossa

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and supratentorial abnormalities.

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The Dandy-Walker spectrum malformations,

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they are varied to more pronounced

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posterior fossa malformations,

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possibly with genetic associations

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of the supratentorial findings

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or a very mild abnormality.

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Then, there's posterior fossa arachnoid cysts,

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which can be confused with

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the Dandy-Walker spectrum malformation

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if you don't pay attention to the

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development of the cerebellar vermis.

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And then, we also discuss several other entities,

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such as Joubert syndrome or

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rhombencephalosynapsis,

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that round out a variety of

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posterior fossa malformations that

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at first may sound confusing,

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but hopefully, you make more sense now.