Dandy-Walker variant

Dandy-Walker variant (DWv) is a less severe posterior fossa anomaly than the classic Dandy-Walker malformation (DWM), characterized as partial vermian hypoplasia with partial obstruction to the fourth ventricle. It is considered on the lesser end of the disease spectrum in the Dandy-Walker continuum.

Terminology

This term 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 ⁴.

Please refer to isolated inferior vermian hypoplasia for a broad discussion in this defined entity.

Pathology

There is usually partial vermian hypoplasia with partial obstruction to the fourth ventricle, but without enlargement of the posterior fossa.

Radiographic features

Antenatal ultrasound

• the diagnosis of a Dandy-Walker variant can not be made definitely until the 18^th week of gestation as the inferior vermis does not form till then
• may show a connection between the cisterna magna and fourth ventricle
• the fourth ventricle is large but less dilated and better formed than the classic Dandy-Walker malformation ¹
• the cerebellar hemispheres are hypoplastic but there is less severe hypoplasia of the inferior vermis

Differential diagnosis

On antenatal ultrasound consider:

• communication between the fourth ventricle and the cisterna magna can be a normal finding up to ~18 weeks of gestation
• incorrect angulation of the scan may make the posterior fossa larger than usual

See also

• Dandy-Walker continuum
• classic Dandy-Walker malformation
• classification system for malformations of the cerebellum