Anatomy of the brain ventricles
The ventricular system consists of four main cavities that are sequentially connected to each other.
Lateral ventricles (Ventriculi laterales) Located within the cerebral hemispheres. Each of them has a complex shape and consists of several parts:
- Anterior (frontal) horn (Frontal horn);
- Body (Body);
- Trigone (Trigone) — the area where the body transitions into the posterior and inferior horns;
- Posterior (occipital) horn (Occipital horn);
- Inferior (temporal) horn (Temporal horn).
The lateral ventricles communicate with the third ventricle via the paired interventricular foramina of Monro (Foramen of Monro).
Third ventricle (Ventriculus tertius) A small slit-like cavity located along the midline. Its lateral wall and floor are formed by the hypothalamus (including structures such as the optic chiasm, pituitary stalk, tuber cinereum, and mammillary bodies). The third ventricle has characteristic outpouchings — recesses:
- Anterior: optic and infundibular recesses;
- Posterior: pineal and suprapineal recesses.
From the third ventricle, CSF flows into the fourth ventricle through a narrow channel — the cerebral aqueduct (aqueduct of Sylvius, Cerebral aqueduct of Sylvius).
Fourth ventricle (Ventriculus quartus) Has a rhombus-like shape. Its tented peak is called the fastigium (fastigium). From this cavity, the cerebrospinal fluid enters the subarachnoid space through three apertures:
- Paired lateral apertures — foramina of Luschka (Foramina of Luschka);
- Unpaired median aperture — foramen of Magendie (Foramen of Magendie).
Choroid plexuses and CSF circulation
Choroid plexus (Choroid plexus) is a specialized vascular membrane composed of pial and ependymal layers. This is where the bulk of CSF is produced. Plexuses are present in the lateral ventricles, from where they pass through the foramina of Monro into the third ventricle (forming its roof). In the fourth ventricle, the plexus extends into the lateral recesses and often protrudes outward through the foramina of Luschka.
Pathway of cerebrospinal fluid: Lateral ventricles → foramina of Monro → III ventricle → cerebral aqueduct → IV ventricle → foramina of Luschka and Magendie → subarachnoid space.
In the subarachnoid space at the base of the brain, CSF accumulates in expanded regions known as subarachnoid cisterns.
The question of CSF reabsorption (absorption) is actively studied today. The classical theory states that the fluid drains into the dural venous sinuses via arachnoid granulations. However, modern studies show that a significant portion of CSF is absorbed along the cranial nerve sheaths, through the cribriform plate into the lymphatic system, and directly into brain capillaries.
Glymphatic system of the brain
Recently, the glymphatic (glial lymphatic) system was described in humans. This is a clearance mechanism of brain tissue that operates as follows:
- CSF moves along pararterial spaces;
- Passes through specialized water channels (aquaporin-4);
- Via bulk flow, it literally "washes" the brain interstitial space, removing metabolic waste products;
- Drainage occurs into perivenous spaces.
Fun fact: the activity of this system increases manifold during sleep and anesthesia, which is one of the main reasons why healthy sleep is critically important for brain function.
Neuroimaging (CT and MRI)
When performing diagnostic imaging of the ventricular system, a number of characteristic features are noted:
- On sagittal T2-weighted MRI scans, the cerebral aqueduct normally shows a flow void (flow void) effect from moving CSF.
- MRI clearly visualizes the structures of the floor of the III ventricle (optic chiasm, pituitary stalk) and the hypothalamic sulcus boundary.
- On axial computed tomography (CT), choroid plexus villi protruding through the foramina of Luschka can often be seen. In adults, these structures frequently undergo physiological calcification, which is a normal imaging finding.
Briefly: answers to topical questions
What anatomical structures form the walls of the third ventricle?
The walls of the third ventricle are formed by the following structures:
- Lateral walls — by the massive gray matter of the thalami.
- Anterior wall — by the terminal plate (lamina terminalis).
- Floor is formed by hypothalamic structures: the optic chiasm, the pituitary infundibulum, the tuber cinereum, and the mammillary bodies.
- Roof is formed by the choroid plexus, which passes through the interventricular foramina into the third ventricle and forms its roof.
What structures form the floor of the fourth ventricle (rhomboid fossa)?
The floor of the fourth ventricle (rhomboid fossa) is located on the dorsal surface of the pons and medulla oblongata. It is bounded laterally by the superior and inferior cerebellar peduncles. The relief of the floor is formed by the following structures:
- Median sulcus and sulcus limitans.
- Medial eminences and facial colliculi (in the rostral part).
- Vestibular areas (in the lateral angles).
- Trigone of hypoglossal nerve and trigone of vagus nerve (in the caudal part).
- Striae medullares — dividing the rostral and caudal parts of the floor.
Class and exam questions
What structures connect the lateral ventricles to the third ventricle?
The lateral ventricles communicate with the third ventricle via the interventricular foramina of Monro (Foramen of Monro).
Through which apertures does CSF leave the ventricular system?
From the fourth ventricle, cerebrospinal fluid enters the subarachnoid space through two paired lateral apertures (of Luschka) and one median aperture (of Magendie).
What is the glymphatic system?
This is a CSF circulation system through paravascular spaces and aquaporin-4 channels that "washes" the brain tissue. Its activity is highest during sleep.
What else to study on this topic
- Topography and nuclei of the hypothalamus (preoptic, anterior, and posterior groups)
- Blood supply to the choroid plexuses of various ventricles
- Structure of the subarachnoid space and basal cisterns
- Anatomy of the dura mater, arachnoid mater, and pia mater
- Connection of the ventricular system with brainstem and cerebellar structures
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