Lateral ventricles

The lateral ventricles are the two largest ventricles of the brain and contain cerebrospinal fluid.

Between the inferior horn and the main body of the ventricle is the putamen, which emerges from the head of the caudate nucleus, and sits above the tapetum; a small number of further connections passing through the occipital tapetum to join the putamen to portions of the caudate nucleus tail adjoining the anterior horn. Below the putamen sits the globus pallidus, with which it connects. These structures bounding the lateral ventricles form a frame curving around the thalamus, which itself constitutes the main structure bounding the third ventricle. Were it not for the choroid plexus, a cleft-like opening would be all that lay between the lateral ventricle and the thalamus; this cleft constitutes the lower part of the choroid fissure. The thalamus primarily communicates with the structures bounding the lateral ventricles via the globus pallidus, and the anterior extremities of the fornix (the mamillary bodies).

Body of the lateral ventricle

thumb|upright=0.7|Body of lateral ventricle shown in red.

The body of the lateral ventricle, or central part is the part of the ventricle between the anterior horn and the trigone. Its roof is bound by the tapetum of the corpus callosum - and is separated medially from the other lateral ventricle by the septum pellucidum. The tail of the caudate nucleus forms the upper portion of the lateral edge, but it is not large enough to cover the whole boundary. Immediately below the tail of the caudate nucleus, the next portion of the lateral edge is formed by the comparatively narrow stria terminalis, which sits upon the superior thalamostriate vein. The main part of the fornix of the brain forms the next narrow portion of the lateral boundary, which is completed medially by a choroid plexus, which serves both ventricles.

Trigone of the lateral ventricle

thumb|upright=0.7|Trigone of lateral ventricle shown in red.

The trigone of the lateral ventricle is the area where the part of the body forms a junction with the inferior horn and the posterior horn. This area is referred to as the atrium of the lateral ventricle, and is where the choroid plexus is enlarged as the choroid glomus. As a triangular surface feature of the floor of this part of the lateral ventricle it is known as the collateral trigone.

Posterior horn of the lateral ventricle

thumb|upright=0.7|Posterior horn shown in red.

The posterior horn of lateral ventricle, or occipital horn, impinges into the occipital lobe in a posterior direction, initially laterally but subsequently curving medially and lilting inferiorly on the lateral side. The tapetum of the corpus callosum continues to form the roof, which due to the lilt is also the lateral edge. However, the posterior and anterior ends of the corpus callosum are characterized by tighter bundling, known as forceps (due to the resulting shape), to curve around the central sulci; the edge of these forceps form the upper part of the medial side of the posterior horn. The remainder of the medial edge of the ventricle is directly in contact with white matter of the cortex of the occipital lobe.

Inferior horn of the lateral ventricle

thumb|upright=0.7|Inferior horn shown in red.

The inferior horn of the lateral ventricle, or temporal horn, is the largest of the horns. It extends anteriorly from the atrium beneath the thalamus and terminates at the amygdala. In the lateral ventricles, specialized areas – choroid plexuses – appear, which produce cerebrospinal fluid. The neural canal that does not expand and remains the same at the level of the midbrain superior to the fourth ventricle forms the cerebral aqueduct. The fourth ventricle narrows at the obex (in the caudal medulla), to become the central canal of the spinal cord.

During development, pressure from exterior structures causes a number of concave bulges to form within the lateral ventricles, which can be extremely variable in their degree of development; in some individuals they are ill-defined, while in others they can be prominent:

from the forceps against the posterior horn - creating the bulb of the posterior cornu on the upper medial side of the horn
from the calcarine sulcus against the posterior horn - creating the calcar avis (historically called the hippocampus minor, for visual reasons) on the lower medial side of the horn
from the hippocampus against the inferior horn (on the medial floor of the horn)
from the collateral sulcus against the inferior horn - creating the collateral eminence on the lateral floor of the horn.

Fetal lateral ventricles may be diagnosed using linear or planar measurements.

Clinical significance

The volume of the lateral ventricles is enlarged in some neurological diseases, such as schizophrenia, bipolar disorder, major depressive disorder,

Ventriculomegaly is a brain condition that mainly occurs during development when the lateral ventricles become dilated.

Asymmetry as an anatomical variation, in the size of the lateral ventricles is found in about 5–12% of the population. This has been associated with handedness, where right-handed people have been found to have a larger right lateral ventricle and a longer left posterior horn, whereas left-handed people have been found to have longer right posterior horns.

Additional images

File:Lateral ventricle small.gif|Position of lateral ventricles (shown in red)

File:Gray735.png|Drawing of a cast of the ventricular cavities, viewed from above

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