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mega_cisterna_magna

Mega cisterna magna

Mega cisterna magna 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.

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. Adults with isolated mega cisterna have an overall normal cognitive functioning but may score inferior to controls on some parameters of memory and verbal fluency. Although application of adult cases to the fetuses is not well established, this information might be of value in parental counseling in cases of a fetus with this anomaly 1).

Pathology

Some authors have proposed that mega cisterna magna is a result of a delayed Blake's pouch fenestration; when this fenestration does not occur it results in a Blake's pouch cyst.

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

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. The cisterna magna usually measures >10 mm on midsagittal images. An enlarged posterior fossa can sometimes be present.

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's pouch cyst: usually a hydrocephalus is present

pilocytic astrocytoma: if very posterior and predominantly cystic.

Case reports

A 21-year-old female had a 3-year history of refractory psychotic symptoms despite adequate antipsychotic treatment. CT and MRI scans disclosed 'mega-cisterna magna'. Thorough neuropsychological testing recorded extensive deficits. Treatment with amisulpride 1200 mg/day resulted in a 30% decrease in PANSS score within 2 months. Then galantamine 8 mg/day was added and PANSS score decreased further by 27% within 2 weeks. Cognitive and social functioning was overall much improved. The effect was sustained in a 24 months follow-up. It is postulated that even a less extended cerebellar lesion, such as mega-cisterna magna, can be associated with psychosis, and in some cases with treatment refractoriness or cognitive dysfunction. Adjuvant galantamine may improve cognitive and psychosocial functioning in these patients 2).

1)
Zimmer EZ, Lowenstein L, Bronshtein M, Goldsher D, Aharon-Peretz J. Clinical significance of isolated mega cisterna magna. Arch Gynecol Obstet. 2007 Nov;276(5):487-90. Epub 2007 Apr 24. PubMed PMID: 17453222.
2)
Ferentinos PP, Kontaxakis VP, Havaki-Kontaxaki BJ, Paplos KG, Pappa DA, Soldatos CR. Refractory psychosis and prominent cognitive deficits in a patient with mega-cisterna magna. Prog Neuropsychopharmacol Biol Psychiatry. 2007 Mar 30;31(2):561-3. Epub 2006 Dec 5. PubMed PMID: 17150294.
mega_cisterna_magna.txt · Last modified: 2019/09/11 08:31 by administrador