Meninges & CSF

Meninges & CSF

Meningeal Layers

See: Brain Atlas: Meninges

Layers

From outside to inside

Meningeal spaces

Spaces

From outside to inside

Anatomy of the cerebral ventricles

Body is the long superior bend.
Atrium (aka trigone) is the convergence of the body, and temporal and occipital horns.
3rd ventricle in midline.
Diamond-shaped 4th ventricle.
Narrow cerebral aqueduct (of Sylvius) connects the 3rd and 4th ventricles.
The 4th ventricle empties into the central canal of the spinal cord.

Floor of the fourth ventricle is its anterior border: an anatomically important site because of its proximity to numerous key brainstem structures (eg, the locus coeruleus and the area postrema). Pressure on the floor of fourth ventricle triggers vomiting via the area postrema.
Superior–posterior border of the fourth ventricle is the superior medullary velum (aka anterior medullary velum), often the site of medulloblastoma.
Inferior–posterior border is the inferior medullary velum (aka posterior medullary velum).
Cerebellar peduncles form the lateral borders of the fourth ventricle and the cerebellum helps form the rest of the posterior border (the roof).

Physiological flow of CSF through the ventricular system.

The choroid plexus is the highly vascularized secretory epithelial tissue that produces cerebrospinal fluid (CSF).
Choroid plexus lies centrally: in the body, atrium, and temporal horn of the lateral ventricle, and the third and fourth ventricles.

It comprises tight junctions within its cuboidal epithelium that form an important blood–cerebrospinal fluid barrier.
There is a lack of choroid plexus in the frontal and occipital horns.
This makes them the ideal site for intraventricular drain placement because the drain won't accidentally tear the highly vascularized choroid plexus.
The choroid plexus is formed where invaginations of vascularized meninges, called tela choroidea, merge with ventricular ependyma. The tela choroidea are variably defined histologically as either combinations of pia and ependyma or double pial layers.

CSF Flow Summary

Empties from the lateral ventricles through the paired foramina of Monro into the third ventricle, down the cerebral aqueduct, and then into the fourth ventricle.
From there, CSF empties into the subarachnoid space through the foramen of Magendie (in midline) and the bilateral foramina of Luschka (laterally), and also show that it empties down the central canal.

The obex is where the 4th ventricle transitions into the central canal of the spinal cord. It lies at the inferior angle of the fourth ventricle, at the level of the gracile tubercle (the swelling formed by the gracile nucleus in the posterior wall of the medulla).

Clinical correlations