The median aperture, or foramen of Magendie, is a single opening in the lower roof of the fourth ventricle. It is the main exit through which cerebrospinal fluid leaves the ventricular system and enters the cisterna magna behind the medulla.
| Location | Midline of the inferior roof of the fourth ventricle, just above the obex, opening into the cisterna magna |
|---|---|
| Parts |
|
| Connections |
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| Blood Supply | Posterior inferior cerebellar artery branches (nearby choroid plexus) |
Lets cerebrospinal fluid flow out of the fourth ventricle into the subarachnoid space around the brainstem and spinal cord.
Failure of the median and lateral apertures to open in development is part of the Dandy-Walker spectrum and causes enlargement of the fourth ventricle and hydrocephalus. Scarring after meningitis or subarachnoid haemorrhage can close the apertures. Neurosurgeons may open a membrane over the foramen of Magendie during posterior fossa decompression.
Blockage of the fourth ventricle apertures by membranes or scarring causing hydrocephalus of all four ventricles.
A congenital condition associated with failure of the fourth ventricle roof and outlets to develop normally, causing a cystic fourth ventricle.
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