Third ventricle

Last revised by Rohit Sharma on 20 Feb 2024

The third ventricle is one of the four CSF-filled cavities that together comprise the ventricular system. It communicates with the paired lateral ventricles and unpaired fourth ventricle.

The third ventricle is a median cleft between the two thalami, which make up the superior aspect of the lateral walls. The thalami are separated from the hypothalamus (anteriorly) and subthalamus (posteriorly) by the hypothalamic sulcus, a groove on the lateral walls of the third ventricle. The size of the third ventricle varies from 2 to 10 mm and enlarges with age 4. A third ventricle size of more than 10 mm is considered dilated 5.

There are two small anterior recesses and two small posterior recesses:

The third ventricle contains a choroid plexus along its roof along the tela choroidea continuous with the choroid plexus from the lateral ventricles.

It communicates with the following:

The anterior wall of the third ventricle is formed from superior to inferior by the columns of the fornix, the anterior commissure, and the lamina terminalis 4.

Posteriorly, it is bounded from superior to inferior by the habenular commissure, the pineal gland, and the posterior commissure.

The roof is formed by the choroidal fissure and the bodies of the fornix 4.

The floor is bounded from anterior to posterior by the optic chiasm (posterior aspect), infundibulum of the pituitary gland, tuber cinereum, mammillary bodies and tegmentum of the midbrain.

The lateral walls are formed by the thalamus, hypothalamic sulcus and hypothalamus.

The third ventricle has a small slit or opening that allows communication between the two thalami, commonly known as the interthalamic adhesion. Although often considered an anatomical variant, most published literature has found that the interthalamic adhesion is present more often than not. As such, it can be considered normal anatomy 6.

The infundibular recess can vary in its invagination into the infundibulum, most commonly extending the entire length. While less commonly 50% or <50% of the length of the infundibular stalk can also occur 3.

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Cases and figures

  • Figure 1: ventricular system
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  • Figure 3: ventricles superimposed on lateral brain
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  • Figure 4: coronal brain through 3rd ventricle
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  • Figure 5: pineal region anatomy
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