Ventricles and Cerebrospinal Fluid (CSF)

Learning Objectives

Identify the ventricles of the brain and their embryonic origin.
Describe the flow of CSF through the adult brain and spinal cord.
Describe the choroid plexus.
Differentiate between CSF and plasma in terms of chemical composition.
Explain how CSF returns to the venous system.

Overview of the Ventricles and CSF

The ventricles of the brain are a series of interconnected, fluid-filled spaces (). The ventricular system is composed of paired lateral ventricles, the third ventricle, and the fourth ventricle. These four cavities develop from the lumen of the embryonic neural tube. The choroid plexus found within the ventricles produces cerebrospinal fluid (CSF) which fills the ventricular spaces and the subarachnoid space. The CSF moves through the ventricular system and the subarachnoid space via small foramen that connects all four ventricles. It is eventually returned to the venous circulation through arachnoid villi found in the subarachnoid layer of the meninges.

Fig. 7.1 (a,b) The ventricular system is a series of interconnected spaces filled with CSF. CSF, cerebrospinal fluid. (Reproduced with permission from Baehr M, Frotscher M. Duus’ Topical Diagnosis in Neurology. 4th edition. © Thieme 2005.)

Ventricles

The paired lateral ventricles develop in the lumen of the prosencephalon and are the largest of the cavities making up the ventricular system. The single third ventricle develops in the diencephalon and the unpaired fourth ventricle originates in developing rhombencephalon. The fourth ventricle narrows at the caudal end to form the central canal of the spinal cord. The four ventricles communicate with one another through foramina. The fourth ventricle also connects to the subarachnoid space of the brain and spinal cord via apertures. The cerebral ventricular network facilitates the movement and resorption of CSF.

The lateral ventricles are large C-shaped structures that reside in each of the cerebral hemispheres. Each lateral ventricle has five distinctive parts, anterior horn, body, posterior horn, inferior horn, and atrium ( a).
- The lateral ventricles communicate with the third ventricle by way of the interventricular foramen (foramina of Monro) ( b, c).
The third ventricle is a narrow, single structure in the midline of the brain.
- A circular-shaped structure in the center of the ventricle when viewed from the lateral aspect represents the interthalamic adhesion. The interthalamic adhesion is a commissure connecting the two thalamic lobes.
- The third ventricle communicates with the fourth ventricle through the cerebral aqueduct (aqueduct of Sylvius) ( b, c).
The fourth ventricle lies between the cerebellum posteriorly and the pons and medulla anteriorly. Rostrally, it connects to the cerebral aqueduct and caudally, it narrows into the central canal of the spinal cord (b, c).
- There are three apertures connecting the fourth ventricle, and thus the entire ventricular system, with the subarachnoid space. The apertures are the unpaired median aperture (foramen of Magendie) and the paired lateral apertures (foramina of Luschka).
  - The apertures of the fourth ventricle allow communication with large subarachnoid cisterns.
  - The median aperture connects the fourth ventricle with the cisterna magna.
  - The lateral apertures connect the fourth ventricle with the pontine cistern.
The central canal is derived from the primitive neural tube.
- The central canal extends from the fourth ventricle to the conus medullaris of the spinal cord.
- It is lined with ependymal cells and contains CSF.
- Its function is not clearly understood in humans.
- By the second decade, it fills with cellular debris and is no longer patent.

Fig. 7.2 (a) The ventricular system is a continuation of the central spinal canal into the brain. Cast specimens are used to demonstrate the connections between the four ventricular cavities. Superior view. (b) The lateral ventricles communicate with the third ventricle via the interventricular foramen. The third ventricle communicates with the fourth ventricle through the cerebral aqueduct. (c) The fourth ventricle narrows into the central canal of the spinal cord. (Modified with permission from Gilroy AM, MacPherson BR. Atlas of Anatomy. Third Edition. © Thieme 2016. Illustrations by Markus Voll and Karl Wesker.)

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