Isolated inferior vermian hypoplasia

Last revised by Mostafa Elfeky on 4 Dec 2020

Isolated inferior vermian hypoplasia (IIVH), also referred as part of Dandy-Walker variant (DWV), is a congenital malformation characterized by partial absence of the inferior portion of the cerebellar vermis.

The term Dandy-Walker variant was created to include those malformations that do not meet the criteria for Dandy Walker malformation, however, some authors recommend to avoid it as there is a lack of specificity that may create some confusion. Instead, a more detailed anatomic description is recommended 1,2

In a recent review on this subject, Robinson proposed that the term isolated inferior vermian hypoplasia should also be abandoned in favor of simply vermian hypoplasia or vermian dysplasia unless it can be proved that it is the inferior vermis that is deficient 4

It has still some controversy about the real outcome of these patients, however recent studies have shown a normal cognitive, language, social and behavioral outcomes for them. Mild functional deficits in fine motor activity and receptive language may be present in about 25% of patients 1-3

There is usually partial vermian hypoplasia, specifically on its inferior portion. The remainder of the vermis, the cerebellar hemispheres, the 4th ventricle, and the posterior fossa, have a normal size and architecture 1.

  • the diagnosis of an IIVH cannot be made definitely until the 18th week of gestation as the inferior vermis does not form until then 1,3
  • Dandy-Walker malformation
    • cephalad rotation of the vermian remnant
    • cystic dilatation of the fourth ventricle extending posteriorly 
    • enlarged posterior fossa with torcular-lambdoid inversion 
  • Blake pouch cyst
    • no vermian hypoplasia or rotation

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