Mega cisterna magna
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.
On this page:
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
However, when a mega cisterna magna occurs as an isolated finding with normal ventricles, the prognosis is good.
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.
Differential diagnosis
Mega cisterna magna needs to be distinguished from other causes of an enlarged retrocerebellar CSF space:
- arachnoid cyst
- 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
Related Radiopaedia articles
Anatomy: Brain
-
brain
- grey matter
- white matter
-
cerebrum
-
cerebral hemisphere (telencephalon)
- cerebral lobes and gyri
- frontal lobe
- parietal lobe
-
occipital lobe
- occipital pole
- lingual gyrus
- fusiform gyrus (Brodmann area 37)
- calcarine (visual) cortex
- cuneus
- temporal lobe
- basal forebrain
- limbic system
- insula
-
cerebral sulci and fissures (A-Z)
- calcarine fissure
- callosal sulcus
- central (Rolandic) sulcus
- cingulate sulcus
- collateral sulcus
- inferior frontal sulcus
- inferior occipital sulcus
- inferior temporal sulcus
- interhemispheric fissure
- intraparietal sulcus
- lateral (Sylvian) sulcus
- lateral occipital sulcus
- marginal sulcus
- occipitotemporal sulcus
- olfactory sulcus
- paracentral sulcus
- paraolfactory sulcus
- parieto-occipital fissure
- posterior parolfactory sulcus
- precentral sulcus
- preoccipital notch
- postcentral sulcus
- rhinal sulcus
- rostral sulcus
- subparietal sulcus
- superior frontal sulcus
- superior occipital sulcus
- superior temporal sulcus
- cortical histology
- cerebral lobes and gyri
- white matter tracts
- deep grey matter
-
pituitary gland
- posterior pituitary and stalk (part of diencephalon)
- anterior pituitary
- inferior hypophyseal arterial circle
- diencephalon
-
cerebral hemisphere (telencephalon)
-
brainstem
- midbrain (mesencephalon)
- pons (part of metencephalon)
- medulla oblongata (myelencephalon)
- white matter
-
grey matter
- non-cranial nerve
-
cranial nerve nuclei
- oculomotor nucleus
- Edinger-Westphal nucleus
- trochlear nucleus
- motor nucleus of CN V
- mesencephalic nucleus of CN V
- main sensory nucleus of CN V
- spinal nucleus of CN V
- abducent nucleus
- facial nucleus
- superior salivatory nucleus
- cochlear nuclei
- vestibular nuclei
- inferior salivatory nucleus
- solitary tract nucleus
- ambiguus nucleus
- dorsal vagal motor nucleus
- hypoglossal nucleus
-
cerebellum (part of metencephalon)
- vermis
- cerebellar hemisphere
- cerebellar peduncles
- cranial meninges (meninx primitiva)
- CSF spaces
-
cranial nerves (mnemonic)
- olfactory nerve (CN I)
- optic nerve (CN II)
- oculomotor nerve (CN III)
- trochlear nerve (CN IV)
- trigeminal nerve (CN V) (mnemonic)
- abducens nerve (CN VI)
- facial nerve (CN VII) (segments mnemonic | branches mnemonic)
-
vestibulocochlear nerve (CN VIII)
- vestibular ganglion (Scarpa's ganglion)
- glossopharyngeal nerve (CN IX)
- vagus nerve (CN X)
- spinal accessory nerve (CN XI)
- hypoglossal nerve (CN XII)
- functional neuroanatomy
- CNS development
- cerebral vascular supply
- arteries
- vascular territories
-
circle of Willis
- internal carotid artery (ICA) (segments)
- vertebral artery
-
normal variants
- intracranial arterial fenestration
- internal carotid artery (ICA)
- anterior cerebral artery (ACA)
- middle cerebral artery (MCA)
- posterior cerebral artery (PCA)
- basilar artery
- persistent carotid-vertebrobasilar artery anastomoses (mnemonic)
-
cerebral venous system
-
dural venous sinuses
- basilar venous plexus
- cavernous sinus (mnemonic)
- clival diploic veins
- inferior petro-occipital vein
- inferior petrosal sinus
- inferior sagittal sinus
- intercavernous sinus
- internal carotid artery venous plexus of Rektorzik
- jugular bulb
- marginal sinus
- occipital sinus
- sigmoid sinus
- sphenoparietal sinus
- straight sinus
- superior petrosal sinus
- superior sagittal sinus
- torcula herophili
- transverse sinus
-
cerebral veins
-
superficial veins of the brain
- superior cerebral veins (superficial cerebral veins)
- inferior cerebral veins
- superficial middle cerebral vein
- superior anastomotic vein (of Trolard)
- inferior anastomotic vein (of Labbe)
-
superficial veins of the brain
- deep veins of the brain
- normal variants
-
dural venous sinuses
- arteries
- glymphatic pathway