Sagittal T1-weighted image of the normal brain showingtypical flow of cerebrospinal fluid (CSF).
In T1-weighted magnetic resonance imaging sequences, CSF is black. From the paired lateral ventricles (LV), CSF passes through the paired interventricular foramina of Monro (yellow arrow) into the single midline third ventricle (TV). CSF then flows down the single midline aqueduct of Sylvius (a channel shaped like a toothpick and slender in all diameters; green arrow) into the single midline fourth ventricle (FV). CSF leaves the ventricular system through the two lateral foramina of Luschka and the midline foramen of Magendie. Here, CSF is shown exiting through the foramen of Magendie (blue arrow) and entering the cisterna magna (CM). Within the subarachnoid space (SAS), CSF flows over the convexities of the brain and the folia of the cerebellum, and around the brainstem (curved arrows). From the CM, CSF also courses inferiorly to surround the spinal cord (orange arrow).