Question:hard
Identify the condition shown in the CT scan image below.
Identify the condition shown in the CT scan image below.
Show Hint
Vermian agenesis + cystic 4th ventricle + enlarged posterior fossa.
Updated On: Jun 24, 2026
- Dandy-Walker malformation
- Cerebellar vermis hypoplasia
- Mega cisterna magna
- None
Show Solution
The Correct Option is A
Solution and Explanation
Step 1: Approach the posterior fossa cystic malformations as a spectrum and look for the most severe combination of findings on the scan.
Step 2: Dandy-Walker malformation is defined by three features visible here: an absent or hypoplastic cerebellar vermis, a cyst formed by the dilated fourth ventricle that balloons into a widened posterior fossa, and elevation of the tentorium with the cerebellar hemispheres pushed apart. The presence of all of these together points to Dandy-Walker malformation, so option A is the answer.
Step 3: Distinguish it from the look-alikes. Cerebellar vermis hypoplasia alone shows a small vermis without the large communicating cyst or enlarged fossa. Mega cisterna magna is just a roomy cisterna magna with a normal vermis and fourth ventricle. The combined severe findings rule both of these out.
\[\boxed{\text{Dandy-Walker malformation}}\]
Step 2: Dandy-Walker malformation is defined by three features visible here: an absent or hypoplastic cerebellar vermis, a cyst formed by the dilated fourth ventricle that balloons into a widened posterior fossa, and elevation of the tentorium with the cerebellar hemispheres pushed apart. The presence of all of these together points to Dandy-Walker malformation, so option A is the answer.
Step 3: Distinguish it from the look-alikes. Cerebellar vermis hypoplasia alone shows a small vermis without the large communicating cyst or enlarged fossa. Mega cisterna magna is just a roomy cisterna magna with a normal vermis and fourth ventricle. The combined severe findings rule both of these out.
\[\boxed{\text{Dandy-Walker malformation}}\]
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