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Mega cisterna magna

A mega cisterna magna refers to adult patients with significantly enlarged CSF retrocerebellar cisterns in the posterior fossa with normal cerebellar morphology. Controversy remains around whether mega cisterna magna is a normal anatomical variant or due to volume loss of the cerebellum 1

Some propose the concept that a cisterna magna should enlarge only in response to volume loss of a damaged cerebellum 1

Mega cisterna magna has also been referred to as Blake's pouch or retrocerebellar arachnoid pouch 6

Epidemiology

A mega cisterna magna is thought to occur in ~1% of all brains imaged postnatally. 

Associations

Especially if noted antenatally, a mega cisterna magna has been associated with:

  • infarction
  • inflammation and infection - particularly cytomegalovirus
  • chromosomal abnormalities - especially trisomy 18

Radiographic features

CT / MRI

Typically seen as prominent retrocerebellar cerebrospinal fluid (CSF) appearing space with a normal vermis and normal cerebellar hemispheres

Ultrasound

In antenates, mega cisterna magna refers to an enlarged retrocerebellar CSF space, usually exceeding 10mm in antenatal imaging.

History and etymology

The term was first coined by Gonsette et al in 1962, in patients with cerebellar atrophy. 

Differential diagnosis

Mega cisterna magna needs to be distinguished from other causes of an enlarged retro-cerebellar CSF space:


Related articles

Neuroanatomy

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