Mega cisterna magna
Last revised by Yuranga Weerakkody ◉ on 16 Aug 2022
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Citation:
Gaillard F, Weerakkody Y, Niknejad M, et al. Mega cisterna magna. Reference article, Radiopaedia.org (Accessed on 01 Feb 2023) https://doi.org/10.53347/rID-4585
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4585
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Synonyms:
- Enlarged cisterna magna
- Mega cisterna magna
- Mega-cisterna magna
- Megacisterna magna
- Retrocerebellar arachnoid pouch
Mega cisterna magna refers to a normal variant characterized by a truly focal enlargement of the CSF-filled subarachnoid space in the inferior and posterior portions of the posterior cranial fossa. It is an incidental finding on neuroimaging, and no imaging follow up is necessary.
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Epidemiology
A mega cisterna magna is thought to occur in ~1% of all brains imaged postnatally. It constitutes 54% of all cystic posterior fossa malformations 4.
Associations
Especially if noted antenatally, a mega cisterna magna has been associated with:
- infarction
- inflammation/infection: particularly cytomegalovirus
- chromosomal abnormalities: especially trisomy 18
In children, it has also been identified in association with autism spectrum disorder 9,10.
However, when a mega cisterna magna occurs as an isolated finding and the ventricles are normal it should be considered a variant of normal with no prognostic significance.
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Clinical presentation
There are no specific symptoms related to this condition.
Pathology
Some authors have proposed that mega cisterna magna is a result of a delayed Blake pouch fenestration; when fenestration does not occur, it results in a Blake pouch cyst 6.
Radiographic features
Ultrasound
On antenatal ultrasound, mega cisterna magna refers to an enlarged retrocerebellar CSF space:
- usually >10 mm (some consider up to 12 mm within normal limits)
- septa may be seen within a mega cisterna magna, which are thought to be Blake pouch vestigial remnants 3
- the vermis should be closely evaluated to exclude Dandy-Walker continuum abnormalities
CT/MRI
Typically seen as prominent retrocerebellar cerebrospinal fluid (CSF) appearing space with a normal vermis, normal 4th ventricle, and normal cerebellar hemispheres. An enlarged cisterna magna usually measures >10 mm on midsagittal images. An enlarged posterior fossa can sometimes be present 6.
History and etymology
The term was coined by the Belgian neurosurgeon Richard Gonsette (1929-2014) 8 in 1962, in patients with cerebellar atrophy 7.
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Differential diagnosis
Mega cisterna magna needs to be distinguished from other causes of an enlarged retrocerebellar CSF space:
- arachnoid cyst: can be difficult to distinguish from a mega cisterna magna
- epidermoid cyst: often shows a heterogeneous/dirty signal on FLAIR and restricted diffusion
- cerebellar atrophy / cerebellar hypoplasia
- Dandy-Walker malformation: vermis not intact
- Blake pouch cyst: usually hydrocephalus is present
- pilocytic astrocytoma: if very posterior and predominantly cystic; should contain a mural nodule
References
- 1. Epelman M, Daneman A, Blaser SI, Ortiz-Neira C, Konen O et al. Differential diagnosis of intracranial cystic lesions at head US: correlation with CT and MR imaging. Radiographics. ; 26(1): 173-96. doi:10.1148/rg.261055033 [pubmed citation]
- 2. Estroff JA, Scott MR, Benacerraf BR. Dandy-Walker variant: prenatal sonographic features and clinical outcome. Radiology. 1992; 185(3): 755-8. Radiology [pubmed citation]
- 3. Robinson AJ, Goldstein R. The cisterna magna septa: vestigial remnants of Blake's pouch and a potential new marker for normal development of the rhombencephalon. J Ultrasound Med. 2007;26 (1): 83-95. J Ultrasound Med (full text) - Pubmed citation
- 4. Kollias SS, Ball WS, Prenger EC. Cystic malformations of the posterior fossa: differential diagnosis clarified through embryologic analysis. Radiographics. 1993;13 (6): 1211-31. Radiographics (abstract) - Pubmed citation
- 5. Zimmer EZ, Lowenstein L, Bronshtein M et-al. Clinical significance of isolated mega cisterna magna. Arch. Gynecol. Obstet. 2007;276 (5): 487-90. doi:10.1007/s00404-007-0369-6 - Pubmed citation
- 6. Bosemani T, Orman G, Boltshauser E et-al. Congenital abnormalities of the posterior fossa. Radiographics. 2015;35 (1): 200-20. doi:10.1148/rg.351140038 - Pubmed citation
- 7. Gonsette R, Potvliege R, Andre-Balisaux G, Stenuit J. Mega-cisterna magna: Clinical, radiologic and anatomopathologic study. Acta Neurol Psychiatr Belg. 1968. 68: 559-70
- 8. Sindic C, Edan G. Richard E Gonsette (1929-2014). (2015) Multiple sclerosis (Houndmills, Basingstoke, England). 21 (5): 540. doi:10.1177/1352458515572242 - Pubmed
- 9. Rochat MJ, Distefano G, Maffei M, Toni F, Posar A, Scaduto MC, Resca F, Cameli C, Bacchelli E, Maestrini E, Visconti P. Brain Magnetic Resonance Findings in 117 Children with Autism Spectrum Disorder under 5 Years Old. (2020) Brain sciences. doi:10.3390/brainsci10100741 - Pubmed
- 10. Erbetta A, Bulgheroni S, Contarino V, Chiapparini L, Esposito S, Vago C, Riva D. Neuroimaging findings in 41 low-functioning children with autism spectrum disorder: a single-center experience. (2014) Journal of child neurology. 29 (12): 1626-31. doi:10.1177/0883073813511856 - Pubmed
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