Question:hard
Identify the condition shown in the CT scan image below.
Identify the condition shown in the CT scan image below.
Show Hint
Absent vermis plus cystic fourth ventricle in an enlarged posterior fossa.
Updated On: Jun 23, 2026
- Dandy Walker malformation
- Cerebellar vermis hypoplasia
- Mega cisterna magna
- None
Show Solution
The Correct Option is A
Solution and Explanation
Step 1: Focus on the posterior fossa, the lower-back compartment of the skull. The scan shows it abnormally large and filled with a fluid cyst, immediately steering you toward a posterior fossa cystic malformation.
Step 2: Look for the vermis, the midline strip joining the cerebellar halves. Here it is missing or markedly underdeveloped, so the cyst is actually a ballooned fourth ventricle that has opened out into the enlarged fossa.
Step 3: That exact set - absent or tiny vermis, cystic fourth ventricle, big posterior fossa with high tentorium - defines the Dandy-Walker malformation. The cerebellar hemispheres are splayed to the sides by the central cyst.
Step 4: Rule out the mimics. Mega cisterna magna keeps a normal vermis and fourth ventricle with just a roomy cisterna magna, and isolated vermian hypoplasia lacks the large communicating cyst. Neither fits, so the answer is Dandy-Walker malformation.\[\boxed{\text{Dandy Walker malformation}}\]
Step 2: Look for the vermis, the midline strip joining the cerebellar halves. Here it is missing or markedly underdeveloped, so the cyst is actually a ballooned fourth ventricle that has opened out into the enlarged fossa.
Step 3: That exact set - absent or tiny vermis, cystic fourth ventricle, big posterior fossa with high tentorium - defines the Dandy-Walker malformation. The cerebellar hemispheres are splayed to the sides by the central cyst.
Step 4: Rule out the mimics. Mega cisterna magna keeps a normal vermis and fourth ventricle with just a roomy cisterna magna, and isolated vermian hypoplasia lacks the large communicating cyst. Neither fits, so the answer is Dandy-Walker malformation.\[\boxed{\text{Dandy Walker malformation}}\]
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