flow of CSF

cisterns

Cases

normal mri

alzheimer's brain

motor neuron disease

porencephalic cyst

hyrdocephalus

for discussion

more discussion

identifying landmarks

CSF flows out of the fourth ventricle into the subarachnoid space through one of two portals:  the Foramen of Luschka (there are two of these - they are located at the lateral recesses of the fourth ventricle) and the Foramen of Magendie (located at the caudal tip of the fourth ventricle).

CSF fills the subarachnoid space like a balloon.  It bathes the brain (which "floats" in the CSF) and protects it from shock and atmospheric pressure.  Since the arachnoid membrane is not closely attached to the surface of the brain (in contrast to the pial membrane), CSF-filled spaces or cisterns can be found within the various crevices around the brain.  Two prominent cisterns are shown below.  The ambient cisterns are found at the side of the brainstem and receive CSF that exits the fourth ventricle through the Foramen of Luschka.  The cisterna magna is found at the caudal tip of the brain between the cerebellum and medulla.   It receives CSF flowing out of the fourth ventricle through the Foramen of Magendie.



Since cisterns are fluid-filled spaces, they appear dark on CT scans and T1-weighted MRIs.  They thus make useful anatomical landmarks when studying brain images in the clinical setting.