Name the 5 fluid spaces

1. Lateral ventricles: you make roughly half a litre of CSF a day, but only ~150 mL is in your head and spine at any moment (~25 mL in the ventricles), so it is renewed about 3-4 times a day. The choroid plexus is the main source, not the only one.
2. Third ventricle: a colloid cyst in its roof, right at the openings from the lateral ventricles (foramina of Monro), can rarely block CSF flow suddenly: acute hydrocephalus. Most are found by chance.
3. Fourth ventricle: the lower end of its floor holds the area postrema, the chemoreceptor trigger zone for vomiting (a target in NMOSD: intractable hiccups, nausea or vomiting). CSF leaves the ventricles here, through two side openings (Luschka) and one in the midline (Magendie).
4. Temporal horn: normally a barely visible slit, it widens early when CSF backs up. It also widens when the hippocampus shrinks (e.g. Alzheimer's), so a wide horn alone does not mean hydrocephalus.
5. Cerebral aqueduct: ~15 mm long and 1-2 mm wide, the narrowest point of the system. Block it and the lateral and third ventricles swell while the fourth stays normal; aqueductal stenosis is the most common cause of congenital obstructive hydrocephalus.

Every structure in this video belongs to one person: traced from his 7 T MRI (0.25 mm voxels).