“ This is a spectrum of abnormalities ranging from the least severe megacisterna magna to the classic Dandy-Walker malformation. MEGACISTERN...
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This is a spectrum of abnormalities ranging from the least severe megacisterna magna to the classic Dandy-Walker malformation.
MEGACISTERNA MAGNA
- Enlarged cisterna magna crosses beneath the tentorium cerebelli. The posterior fossa may be enlarged. Note: Fourth ventricle, cerebellar vermis and tentorium normal.
HYPOPLASTIC VERMIS WITH ROTATION (ALSO KNOWN AS DANDY-WALKER VARIANT)
- This is more common than Dandy-Walker syndrome. There is a small posterior fossa cyst. The cerebellar vermis is present but hypoplastic, the brainstem is normal and the posterior fossa is not enlarged.
DANDY-WALKER MALFORMATION
- This is a congenital anomaly that is thought to arise from an in utero insult to the fourth ventricle. Associated with callosal dysgenesis or agenesis (25%), holoprosencephaly (25%) or polymicrogyria (25%).
CT/MRI
• Enlarged posterior fossa• Elevated torcula• Cystic enlargement of fourth ventricle• Hypoplastic cerebellum (with or without hypoplastic tentorium)• 80% have hydrocephalus
(a) Axial T2-weighted magnetic resonance image of the brain showing gross enlargement of the fourth ventricle and cerebellar hypoplasia. (b) Sagittal Tl-weighted image in the same patient shows enlargement of the fourth ventricle, enlargement of the posterior fossa (asterisk) and cerebellar hypoplasia (short arrow). The torcula is elevated (long arrow). The appearance is in keeping with a Dandy-Walker malformation.
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