Mega Cisterna Magna

MRI scan showing Mega cisterna magna
MRI scan showing Mega cisterna magna

A mega-cisterna magna, is a controversial entity among experts. In general however, the term is applied to non-pathological prominance (usually exceeding 10 mm in antenatal imaging) of the retro-cerebellar CSF space and not associated with cerebellar abnormalities. There is a normal vermis and normal cerebellar hemispheres.


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


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

  • infarction
  • inflammation and infection (e.g. Cytomegalovirus)
  • chromosomal abnormalities (e.g. trisomy 18)

Radiographic features on CT

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


The term was first coined by Gonsetteet al in 1968, in patients with cerebellar atrophy.

Dandy-Walker malformation: (A, B)The fourth ventricle opens into a large posterior fossa cyst. There is associated hydrocephalus. (C) The cerebellum is hypoplastic & a thin rim of cerebellar tissue is seen forming the wall of the posterior fossa cyst (arrow). The vein of Galen, straight sinus, & venous confluence are elevated above the level of the lambdoid suture.

Differential diagnosis

Differential is among other causes of an enlarged retro-cerebellar CSF space, including:

  • arachnoid cyst
  • epidermoid cyst
  • cerebellar atrophy/cerebellar hypoplasia
  • Dandy-Walker malformation
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Burhan Ahmed is currently Editor-in-Chief at He completed his residency from Michigan State University in 2015. He has written three short revision books on Biology, Stomatology and Gynecology, has 4 publications to his name. He is pursuing career in cosmetic dermatology.


  1. My wife is pregnant 9th month today checking the scanning some brain problem and doctors telling mega cistano magna 16m.m. But i don’t know please tell me anyone help me please

    • 16 mm is only significant if there are other fetal abnormalities. If your downes and trisomy screens were low risk and growth is ok (fetus size) then probably no medical significance


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