The cisterna magna (cerebellomedullary cistern) is the largest subarachnoid cistern, located between the inferior surface of the cerebellum, the dorsal surface of the medulla, and the posterior atlanto-occipital membrane. CSF flows into it from the fourth ventricle through the foramina of Luschka and Magendie. It communicates with the spinal subarachnoid space inferiorly and with the other basal cisterns superiorly.
| Location | Between the underside of the cerebellum and the back of the medulla, just above the foramen magnum |
|---|---|
| Parts |
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| Connections |
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| Blood Supply | Posterior inferior cerebellar artery |
The largest cistern, receiving cerebrospinal fluid as it leaves the fourth ventricle. Its size is checked on fetal ultrasound, and it was once used for cisternal puncture.
The cisterna magna is accessed by cisternal puncture (suboccipital puncture) for CSF sampling when lumbar puncture is contraindicated. It is the standard route for intrathecal drug delivery in some gene therapy and enzyme replacement protocols. Dandy-Walker syndrome involves cystic dilation of the fourth ventricle into the cisterna magna with cerebellar vermis hypoplasia. Mega cisterna magna (isolated enlargement without associated anomalies) is a normal variant. The cisterna magna is the posterior approach entry point in endoscopic third ventriculostomy planning.
Dandy-Walker complex produces cystic dilation of the fourth ventricle that expands into the cisterna magna, displacing the cerebellar vermis superiorly and anteriorly with variable cerebellar hemisphere hypoplasia; ventriculoperitoneal shunting addresses the associated hydrocephalus and MRI characterises the specific extent of the posterior fossa cyst.
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