Third ventricle
The third ventricle is one of the four connected cerebral ventricles of the ventricular system within the mammalian brain. It is a slit-like cavity formed in the diencephalon between the two thalami, in the midline between the right and left lateral ventricles, and is filled with cerebrospinal fluid (CSF).[1]
Third ventricle
Running through the third ventricle is the interthalamic adhesion, which contains thalamic neurons and fibers that may connect the two thalami.
Development[edit]
The third ventricle, like other parts of the ventricular system of the brain, develops from the neural canal of the neural tube. Specifically, it originates from the most rostral portion of the neural tube which initially expands to become the prosencephalon. The lamina terminalis is the rostral termination of the neural tube. After about five weeks, different portions of the prosencephalon begin to take distinct developmental paths from one another – the more rostral portion becomes the telencephalon, while the more caudal portion becomes the diencephalon.[2] The telencephalon gradually expands laterally to a much greater extent than it does dorsally or ventrally, and its connection to the remainder of the neural tube reduces to the interventricula foramina. The diencephalon expands more evenly, but caudally of the diencephalon the canal remains narrow. The third ventricle is the space formed by the expanding canal of the diencephalon.
The hypothalamic region of the ventricle develops from the ventral portion of the neural tube, while the thalamic region develops from the dorsal portion; the wall of the tube thickens and becomes the hypothalamus and thalamus respectively. The hypothalamic area of the ventricle begins to distend ventrally during the 5th week of development, creating the infundibulum and posterior pituitary; an outgrowth from the stomodeum (the future mouth) gradually extends towards it, to form the anterior pituitary.
The optic recess is noticeable by the end of the 6th week, by which time a bend is distinguishable in the dorsal portion of the ventricle border. Rostral of the bend, the medial dorsal portion of the ventrical begins to flatten, and become secretory (i.e. choroid plexus), forming the roof of the ventricle. Caudal of the bend, the ventricle border forms the epithalamus, and begins to distend towards the parietal bone (in lower vertebrates, it distends more specifically to the parietal eye); the border of the distention forms the pineal gland.
Clinical significance[edit]
The floor of the third ventricle is formed by hypothalamic structures and this can be opened surgically between the mamillary bodies and the pituitary gland in a procedure called an endoscopic third ventriculostomy. An endoscopic third ventriculostomy can be performed in order to release extra fluid caused by hydrocephalus.
Several studies have found evidence of ventricular enlargement to be associated with major depression, particularly enlargement of the third ventricle.[3] These observations are interpreted as indicating a loss of neural tissue in brain regions adjacent to the enlarged ventricle, leading to suggestions that cytokines and related mediators of neurodegeneration may play a role in giving rise to the disease.[4][5][6]
A chordoid glioma is a rare tumour that can arise in the third ventricle.[7]
Third ventricle
Coronal section of lateral and third ventricles.
Drawing of a cast of the ventricular cavities, viewed from above.
Third ventricle
