Chapter 11

Within the brain is a communicating system of cavities that are lined with ependyma and filled with cerebrospinal fluid (CSF): There are two lateral ventricles, the third ventricle (between the halves of the diencephalon), the cerebral aqueduct, and the fourth ventricle within the brain stem (Fig 11–1).

###### Figure 11–1

The ventricular system.

### Lateral Ventricles and Choroid Plexus

The lateral ventricles are the largest. They each include two central portions (body and atrium) and three extensions (horns).

The choroid plexus is the site where cerebrospinal fluid (CSF) is produced. It is a fringe-like vascular process of pia mater containing capillaries of the choroid arteries. It projects into the ventricular cavity and is covered by an epithelial layer of ependymal origin (Figs 11–2 and 11–3). The attachment of the plexus to the adjacent brain structures is known as the tela choroidea. The choroid plexus extends from the interventricular foramen, where it joins with the plexuses of the third ventricle and opposite lateral ventricle, to the end of the inferior horn. (There is no choroid plexus in the anterior and posterior horns.)

###### Figure 11–2

Three stages of development of the choroid plexus in the lateral ventricle (coronal sections).

###### Figure 11–3

Dorsal view of the choroid plexus in the ventricular system. Notice the absence of choroid in the aqueduct and the anterior and posterior horns.

The anterior (frontal) horn is in front of the interventricular foramen. Its roof and anterior border are formed by the corpus callosum; its vertical medial wall, by the septum pellucidum; and the floor and lateral wall, by the bulging head of the caudate nucleus.

The central part, or body, of the lateral ventricle is the long, narrow portion that extends from the interventricular foramen to a point opposite the splenium of the corpus callosum. Its roof is formed by the corpus callosum and its medial wall by the posterior portion of the septum pellucidum. The floor contains (from medial to lateral side) the fornix, the choroid plexus, the lateral part of the dorsal surface of the thalamus, the stria terminalis, the vena terminalis, and the caudate nucleus. The atrium, or trigone, is a wide area of the body that connects with the posterior and inferior horns (Fig 11–4).

###### Figure 11–4

Drawing of the ventricles showing their relationship to the dura, tentorium, and skull base.

The posterior (occipital) horn extends into the occipital lobe. Its roof is formed by fibers of the corpus callosum. On ...

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