The MR images below are from a 2-month-old Weimaraner with generalised ataxia including hypermetria in the forelimbs, a tendency to fall to either side, normal paw positioning and normal cranial nerve examination. The images shows a large cystic structure occupying the region that normally contains the cerebellar vermis, which is absent, and extending rostrotentorially, displacing the occipital lobes. The content of the cystic structure has similar signal intensity as CSF. The caudal fossa is enlarged and the osseous tentorium is found more dorsal and rostral than its expected position. The cerebellar hemispheres as well as the corpus callosum are mildly hypoplastic. Not visible in this case, other less common findings with this malformation complex can include widening and irregular gyrification of the cerebral sulci, agenesis / hypoplasia of the septum pellucidum and/or ventricular dilation.

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A classic Dandy-Walker malformation consists of complete or partial agenesis of the cerebellar vermis with an upward displacement and rotation of the remnants of the vermis, cyst-like dilation of the fourth ventricle and enlargement of the posterior fossa, with upward displacement of the tentorium cerebelli osseum, transverse sinuses, and torcula. Hydrocephalus may occur in up to 80% of humans with the disorder. 

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Images courtesy of Esther Lichtenauer from Evidensia Dierenziekenhuis Hart van Brabant.

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Read more about this disorder in 14 closely related Eurasier dogs using the link below.

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