Dandy-Walker variant

 

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Clinical History:
A 29 year old man with Down’s syndrome, and no acute clinical symptomatology relevant to the imaging findings.

Diagnosis:
Dandy-Walker variant

MR Technique:
5 mm unenhanced axial SE T1- and FSE (with 15 echoes) T2- and sagittal SE T1-weighted scans are presented, acquired at 1.5 T on a Siemens Espree MR system. Sequence parameters were TR/TE = 500/12, 5800/96 and 435/14 respectively. Scan times were 3:44, 3:47 and 3:43 min:sec.

Imaging Findings:
The fourth ventricle is prominent, and on the basis of sagittal images there is hypoplasia of the inferior cerebellar vermis. There is an apparent communication between the fourth ventricle and the posterior fossa cyst.

In the classic Dandy-Walker malformation, there is dilatation of the fourth ventricle leading to an enlarged posterior fossa (with elevation of the torcula), and the vermis is hypoplastic and rotated counter clockwise (upwards). However, there is a spectrum of disease severity, from these classic findings to much less severe changes, leading to the use of the terms Dandy-Walker spectrum or Dandy-Walker complex. A mega cisterna magna is sometimes placed at the extreme end of the spectrum, representing the least prominent findings. In the case presented, the findings overall are moderate in degree, with the elevation of the torcula and the hypoplasia of the vermis mild, and no scalloping or remodelling of the occipital bone.