Mega cisterna magna
Updates to Article Attributes
Mega cisterna magna refers to a normal variant characterised 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.
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/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
In antenates, mega cisterna magna refers to an enlarged retrocerebellar CSF space:
- usually >10 mm in antenatal imaging (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
- 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 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 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 a hydrocephalus is present
- pilocytic astrocytoma: if very posterior and predominantly cystic
-<p><strong>Mega cisterna magna</strong> refers to a normal variant characterised by a truly focal enlargement of the subarachnoid space in the inferior and posterior portions of the posterior fossa. It is an incidental finding on neuroimaging, and no imaging follow up is necessary. </p><h4>Epidemiology</h4><p>A mega cisterna magna is thought to occur in ~1% of all brains imaged postnatally. </p><h5>Associations</h5><p>Especially if noted antenatally, a mega cisterna magna has been associated with:</p><ul>- +<p><strong>Mega cisterna magna</strong> refers to a normal variant characterised by a truly focal enlargement of the <a href="/articles/cerebrospinal-fluid-1">CSF</a>-filled <a title="Subarachnoid space" href="/articles/subarachnoid-space">subarachnoid space</a> in the inferior and posterior portions of the <a title="Posterior cranial fossa" href="/articles/posterior-cranial-fossa">posterior cranial fossa</a>. It is an incidental finding on neuroimaging, and no imaging follow up is necessary. </p><h4>Epidemiology</h4><p>A mega cisterna magna is thought to occur in ~1% of all brains imaged postnatally. </p><h5>Associations</h5><p>Especially if noted antenatally, a mega cisterna magna has been associated with:</p><ul>
-</ul><h5>CT/MRI</h5><p>Typically seen as prominent retrocerebellar cerebrospinal fluid (CSF) appearing space with a normal vermis, normal 4<sup>th</sup> ventricle, and normal cerebellar hemispheres. An enlarged cisterna magna usually measures >10 mm on midsagittal images. An enlarged posterior fossa can sometimes be present <sup>6</sup>. </p><h4>History and etymology</h4><p>The term was first coined by <strong>Gonsette et al</strong> in 1962, in patients with cerebellar atrophy. </p><h4>Differential diagnosis</h4><p>Mega cisterna magna needs to be distinguished from other causes of an <a href="/articles/enlarged-posterior-fossa-csf-space">enlarged retrocerebellar CSF space</a>:</p><ul>- +</ul><h5>CT/MRI</h5><p>Typically seen as prominent retrocerebellar <a href="/articles/cerebrospinal-fluid-1">cerebrospinal fluid</a> (CSF) appearing space with a normal vermis, normal 4<sup>th</sup> ventricle, and normal cerebellar hemispheres. An enlarged cisterna magna usually measures >10 mm on midsagittal images. An enlarged posterior fossa can sometimes be present <sup>6</sup>. </p><h4>History and etymology</h4><p>The term was first coined by <strong>Gonsette et al</strong> in 1962, in patients with cerebellar atrophy. </p><h4>Differential diagnosis</h4><p>Mega cisterna magna needs to be distinguished from other causes of an <a href="/articles/enlarged-posterior-fossa-csf-space">enlarged retrocerebellar CSF space</a>:</p><ul>
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