Ventricles anterior view

The ventricular system is viewed from the anterior perspective in this illustration. One can now see both lateral ventricles and the short interventricular foramen (of Monro) on both sides, connecting each lateral ventricle with the midline third ventricle (see Figure 28B and Figure 29). It is important to note that the thalamus (diencepha-lon) is found on either side of the third ventricle (see also Figure 9A).

CSF flows from the third ventricle into the aqueduct of the midbrain. This ventricular channel continues through the midbrain, and then CSF enters the fourth ventricle, which also straddles the midline. The ventricle widens into a diamond-shaped space, when seen from the anterior perspective. This ventricle separates the pons and medulla anteriorly from the cerebellum posteriorly. The lateral recesses carry CSF into the cisterna magna, the CSF cistern outside the brain (see Figure 21), through the foramina of Luschka, the lateral apertures, one on each side. The space then narrows again, becoming a narrow channel at the level of the lowermost medulla, which continues as the central canal of the spinal cord (see Figure 4).

Sections of the brain in the coronal (frontal) axis, if done at the appropriate plane, will reveal the spaces of the lateral ventricles within the hemispheres (see Figure 29 and Figure 74). Likewise, sections of the brain in the horizontal axis, if done at the appropriate level, will show the ventricular spaces of the lateral and third ventricles (see Figure 27). These can also be visualized with radio-

graphic imaging (CT and MRI, see Figure 28A, Figure 28B, and Figure 30).

Clinical Aspect

It is quite apparent that the flow of CSF can be interrupted or blocked at various key points within the ventricular system. The most common site is the aqueduct of the midbrain, the cerebral aqueduct (of Sylvius). Most of the CSF is formed upstream, in the lateral (and third) ventricles. A blockage at the narrowest point, at the level of the aqueduct of the midbrain, will create a damming effect. In essence, this causes a marked enlargement of the ventricles, called hydrocephalus. The CSF flow can be blocked for a variety of reasons, such as developmentally, following meningitis, or by a tumor in the region. Enlarged ventricles can be seen with brain imaging (e.g., CT scan).

Hydrocephalus in infancy occurs not uncommonly, for unknown reasons. Since the sutures of the infant's skull are not yet fused, this leads to an enlargement of the head and may include the bulging of the anterior fontanelle. Clinical assessment of all infants should include measuring the size of the head and charting this in the same way one charts height and weight. Untreated hydrocephalus will eventually lead to a compression of the nervous tissue of the hemispheres and damage to the developing brain. Clinical treatment of this condition, after evaluation of the causative factor, includes shunting the CSF out of the ventricles into one of the body cavities.

In adults, hydrocephalus caused by a blockage of the CSF flow leads to an increase in intracranial pressure (discussed in the introduction to Section C). Since the sutures are fused, skull expansion is not possible. The cause in adults is usually a tumor, and in addition to the specific symptoms, the patient will most commonly complain of headache, often in the early morning.

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k

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LVii

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Po

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F = Frontal lobe

D = Diencephalon (thalamus)

T = Temporal lobe

Md = Midbrain

Ventricles

Cc

Po = Pons

LV = Lateral ventricle

m

M = Medulla

LVi = Inferior horn

3 = 3rd ventricle

Sc

C = Cerebellum

Aq = Aqueduct of midbrain

Sc = Spinal cord

4 = 4th ventricle

Cc = Central canal

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