Anatomy: Posterior Fossa, Hindbrain & Craniocervical Junction
Cisterna magna
The cisterna magna is a CSF-filled space behind the lower brainstem and below the cerebellum, often reduced or effaced in Chiari malformation.
In short: Cisterna magna
- It is a CSF-filled space below the cerebellum and behind the brainstem.
- It is one of the larger CSF reservoirs at the skull base.
- It is often reduced or effaced (compressed) in Chiari.
- Its effacement reflects the crowding at the craniocervical junction.
What it is
The cisterna magna (or cerebellomedullary cistern) is a CSF-filled space located below the cerebellum and behind the lower brainstem, near the foramen magnum. It is one of the larger reservoirs of CSF at the base of the skull, and it is often reduced or compressed in Chiari malformation.
Understanding Cisterna magna
Normally, the cisterna magna provides a roomy, CSF-filled space behind the cervicomedullary junction. In Chiari malformation, the descending cerebellar tonsils crowd this area, so the cisterna magna is often effaced (compressed or obliterated) on imaging — a finding that reflects the crowding at the craniocervical junction. The loss of this normal CSF space is part of why CSF flow is disrupted in Chiari. One goal of posterior fossa decompression surgery is to recreate or restore a more open CSF space in this region (sometimes the duraplasty effectively enlarges the cisterna magna). Understanding the cisterna magna helps clarify both a typical imaging finding in Chiari and an aim of surgery.
Why it matters
Understanding the cisterna magna helps families interpret imaging that describes it as effaced, see how Chiari crowds this CSF space, and recognize that surgery aims to restore a more open space here.
Common questions
What is the cisterna magna?
A CSF-filled space below the cerebellum and behind the brainstem.
What happens to it in Chiari?
It is often reduced or effaced (compressed).
Why does that matter?
Its loss reflects crowding and disrupted CSF flow; surgery aims to restore it.
Bottom line
The cisterna magna is a CSF space below the cerebellum, often effaced in Chiari, whose restoration is an aim of decompression surgery.
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