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mega cisterna magna
Last week a  Brain MRI to my 4-year-old son was performed, I want to know what means: There is evidence of a mega cisterna magna vs an arachnoid cyst.

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Hi jessy,
Mega-cisterna magna is defined as an enlarged cisterna magna with an intact Cerebellar vermis and fourth ventricle. The cisterna magna is a spinal fluid space in the back of the brain; it lies just posterior to the cerebellum.
Arachnoid cysts are cerebrospinal fluid-filled sacs that are located between the brain or spinal cord and the arachnoid membrane.
Any fluid filled collection in posterior part of brain in midline would suggest a differential diagnosis which includes mega cisterna magna and midline posterior fossa arachnoid cysts.
In mega cisterna magna, the cisterna magna is enlarged and communicates freely with the perimedullary subarachnoid space. The fourth ventricle, vermis, and Cerebellar hemispheres are normally formed. The midline posterior fossa arachnoid cysts are retrocerebellar CSF collections that do not communicate with the fourth ventricle and perimedullary subarachnoid spaces.
I want to know the reason to do a MRI?
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Hi.

Mega cisterna magna refers to enlargement of the cisterna magna, a large "space" between the medulla and cerebellum which allows CSF to drain. The enlargement may occur in both normal and pathologic conditions. As an incidental finding, and without any symptoms, it would be difficult to assess its clinical significance.

An arachnoid cyst, on the other hand, are sacs containing cerebrospinal fluid and are located between the arachnoid membrane and spinal cord/brain. Arachnoid cysts are usually classified as primary or secondary. Depending on the location and size, arachnoid cysts could produce symptoms of headache, nause, vomiting, seizures, nerve root compression disorders such as numbness and tingling of extremities, etc.

The MRI should always be correlated with clinical findings to determine its clinical significance.

Consult your neurologist regarding this.

Good luck.
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I would appreciate any comments and thoughts on my post under mega cisterna magna.  I have one and a large extra axial mass which causes some mass effect on my left cerebellum.  I am very symptomatic and so far undiagnosed.  Thanks for any help.
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