Neurosurgery notes/Paediatrics/Developmental abnormalities/Intracranial Anomalies/Posterior Fossa Cystic Malformations/Enlarged/mega cisterna magna

Enlarged/mega cisterna magna

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4th ventricle size
Normal
Status
Done
Communication between 4th and cisterna magna
Yes
Files & media
Untitled picture.pngUntitled picture.png
Hydrocephalus
No
Image explain
enlarged size of the posterior fossa but normal size of the cerebellum.   Down: shows mega cisterna magna (arrow), a normal vermis, a normal fourth ventricle, an enlarged posterior fossa, scalloping of the occipital bone, and the absence of HCP
Intrathecal contrast CT
Communicates with ventricles
Inferior Vermis
Normal
Mass effect on the cerebellar hemisphere
No
Occipital bone scalloping
Possible
Position of choroid plexus
Normal
Vermis remnant
Normal
cerebellar hemispheres
Normal
post fossa size
Enlarged (some)

General

  • Aka: enlarged cisterna magna

Definition

  • an enlarged posterior fossa secondary to an enlarged cisterna magna (>10 mm on midsagittal images),
  • A normal
    • vermis
    • 4th ventricle.
  • in some patients, an enlarged posterior fossa

Pathology

flowchart LR
    
    C[Non-perforation of<br>foramen of Magendie]
    C --> D[4th ventricle enlargement]
    D --> E[Foramina of Luschka<br>eventually opens]
    E --> F[CSF flow from 4th<br>into cisterns]
    F --> G[Focal enlargement of the<br>subarachnoid space in the<br>inferior & posterior portions<br>of the posterior fossa]
    G --> H[Mega cisterna magna freely<br>communicates with 4th and<br>cervical subarachnoid space]
If there is no fenestration of the Blake pouch will results in Blake pouch cyst
Mega cisterna magna freely communicates with the fourth ventricle and the cervical subarachnoid space (can be seen on MRI-CISS studies)

Presentation

  • Incidental finding and represents a normal variant

Evaluation

  • Imaging
    • normal
      • vermis
      • No hydrocephalus
    • Abnormal
      • enlarged posterior fossa secondary to an enlarged cisterna magna.
      • Normal vermis and fourth ventricle and no mass effect on the cerebellum
      notion image
      notion image

Clinical features

  • Incidental (asymptomatic)
  • Ventriculomegaly occurs rarely (2.3%) before or after birth.
    • Very similar to Blake's pouch cyst but mega cisterna magna has no HCP

Treatment

  • There is no role for shunt surgery even if the cisterna magna is extremely large.

Outcomes

  • no reported recurrence risk.
  • 95 of children with isolated mega cisterna magna develop normally