Mega cisterna magna
 Discussion of Mega cisterna magna
- The term mega cisterna magna has been loosely applied to a large retrocerebellar cerebrospinal fluid (CSF)–appearing space with a normal vermis and normal cerebellar hemispheres.
- More recently, the concept that a cisterna magna should enlarge only in response to volume loss of a damaged cerebellum has been revised. It is believed that when such large spaces manifest with mass effect on the cerebellum, enlargement of the posterior fossa and/or splitting of the falx, and supratentorial extension, they can be attributed not to an enlarged subarachnoid cistern but to a space-occupying lesion.
- Mega cisterna magna occurs in approximately 1% of all brains imaged postnatally.
- Mega cisterna magna has been associated with infarction, inflammation, and infection, particularly cytomegalovirus, as well as with chromosomal abnormalities, especially trisomy 18.
- In the absence of other findings to suggest a posterior fossa lesion, a mega cisterna magna is unlikely to be clinically significant.
 Imaging Findings for Mega cisterna magna
- Prominent retrocerebellar cerebrospinal fluid (CSF)–appearing space with a normal vermis and normal cerebellar hemispheres.
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 References for Mega cisterna magna
- Monica Epelman, Alan Daneman, Susan I. Blaser, Clara Ortiz-Neira, Osnat Konen, José Jarrín, and Oscar M. Navarro. Differential Diagnosis of Intracranial Cystic Lesions at Head US: Correlation with CT and MR Imaging. RadioGraphics 2006 26: 173-196.