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| Third ventricle | |
|---|---|
 Third ventricle shown in red | |
 Blue –lateral ventricles Cyan –interventricular foramina (Monro) Yellow – third ventricle Red –cerebral aqueduct (Sylvius) Purple –fourth ventricle Green – continuous with thecentral canal (apertures to subarachnoid space are not visible) | |
| Details | |
| Identifiers | |
| Latin | ventriculus tertius cerebri |
| MeSH | D020542 |
| NeuroNames | 446 |
| NeuroLex ID | birnlex_714 |
| TA98 | A14.1.08.410 |
| TA2 | 5769 |
| FMA | 78454 |
| Anatomical terms of neuroanatomy | |
Thethird ventricle is one of the four connectedcerebral ventricles of theventricular system within themammalian brain. It is a slit-like cavity formed in thediencephalon between the twothalami, in the midline between the right and leftlateral ventricles, and is filled withcerebrospinal fluid (CSF).[1]
Running through the third ventricle is theinterthalamic adhesion, which contains thalamicneurons andfibers that may connect the two thalami.
The third ventricle is a narrow, laterally flattened, vaguely rectangular region, filled withcerebrospinal fluid, and lined byependyma. It is connected at the superior anterior corner to thelateral ventricles, by theinterventricular foramina, and becomes thecerebral aqueduct (aqueduct of Sylvius) at the posterior caudal corner. Since the interventricular foramina are on the lateral edge, the corner of the third ventricle itself forms a bulb, known as theanterior recess (it is also known as thebulb of the ventricle). The roof of the ventricle compriseschoroid plexus, forming the inferior central portion of thetela choroidea; immediately above the superior central portion of the tela choroidea is thefornix.
The lateral side of the ventricle is marked by asulcus – thehypothalamic sulcus – from the inferior side of the interventricular foramina to the anterior side of the cerebral aqueduct. The lateral border posterior/superior of the sulcus constitutes thethalamus, while anterior/inferior of the sulcus it constitutes thehypothalamus. Theinterthalamic adhesion usually tunnels through the thalamic portion of the ventricle, joining together the left and right halves of the thalamus, although it is sometimes absent, or split into more than one tunnel through the ventricle; it is currently unknown whether any nerve fibres pass between the left and right thalamus via the adhesion (it has more resemblance to aherniation than acommissure).
The posterior border of the ventricle primarily constitutes theepithalamus. The superior part of the posterior border constitutes thehabenular commissure, while more centrally it thepineal gland, which regulates sleep and reacts to light levels. Caudal of the pineal gland is theposterior commissure; nerve fibres reach the posterior commissure from the adjacent midbrain, but their onward connection is currently uncertain. The commissures create concavity to the shape of the posterior ventricle border, causing thesuprapineal recess above the habenular, and the deeper pineal recess between the habenular and posterior commissures; the recesses being so-named due to the pineal recess being bordered by the pineal gland.
The anterior wall of the ventricle forms thelamina terminalis, within which thevascular organ monitors and regulates theosmotic concentration of the blood; the cerebrum lies beyond the lamina, and causes it to have a slightly concave shape. Theoptic recess – marks the inferior end of the lamina terminalis, with theoptic chiasm forming the immediately adjacent floor.
The portion of the floor immediately posterior of the optic chiasm distends inferiorly, and slightly anteriorly, to form a funnel (theinfundibulum); the recess leading to the funnel is known as theinfundibular recess. The border of the funnel is thetuber cinereum, which constitutes a bundle of nerve fibres from the hypothalamus. The funnel ends in theposterior lobe of thepituitary gland, which is thus neurally connected to the hypothalamus via the tuber cinereum. Avenous sinus (thecircular sinus) surrounds the superior portion of the tuber cinereum; thecircular sinus is in fact simply a portion of the two lateralcavernous sinuses, joined together by a posterior and anteriorintercavernous sinus.
Themammillary bodies form the floor posterior of the tuber cinereum, acting as the link between the fornix and the hypothalamus. Posterior of the mamillary bodies, the ventricle becomes the opening of the cerebral aqueduct, the inferior borders becoming thecrus cerebri (sometimes historically called thecerebral peduncle) of themidbrain.
The third ventricle, like other parts of the ventricular system of the brain, develops from theneural canal of theneural tube. Specifically, it originates from the most rostral portion of the neural tube which initially expands to become theprosencephalon. 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 thetelencephalon, while the more caudal portion becomes thediencephalon.[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 thestomodeum (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 theparietal eye); the border of the distention forms the pineal gland.
The floor of the third ventricle is formed by hypothalamic structures and this can be openedsurgically between themamillary bodies and thepituitary gland in a procedure called anendoscopic third ventriculostomy. An endoscopic third ventriculostomy can be performed in order to release extra fluid caused byhydrocephalus.
Several studies have found evidence of ventricular enlargement to be associated with majordepression, 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 thatcytokines and related mediators ofneurodegeneration may play a role in giving rise to the disease.[4][5][6]
Achordoid glioma is a rare tumour that can arise in the third ventricle.[7]
