General
- Controversial Nomenclature
- A more useful, functional definition of CIM includes Chiari 1.5 (and Chiari 0), classifying them all as representing some degree of acquired obstruction at the level of the foramen magnum by the inferior cerebellum.
Definition
- Characterised by the caudal displacement (herniation) of structures below the foramen magnum, including:
- Cerebellar tonsils.
- Brainstem (specifically the medulla).
- Fourth ventricle (Descent of the obex (the lowermost point of the fourth ventricle and medulla)).
- A key differentiating factor is that this condition occurs without spina bifida, which distinguishes it from the more severe Chiari 2
- Chiari 1.5 is sometimes referred to as "complex Chiari" because it encompasses more than just the tonsillar descent typically seen in standard Chiari 1.
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