Anatomy and topography of cavities
The ventricular system consists of several compartments located in different parts of the brain. Key structural elements:
- Lateral ventricles (ventriculi laterales). They are located deep within the cerebral hemispheres. Their structure comprises anterior horn (cornu anterius), which extends into the frontal lobe, inferior horn (cornu inferius), descending into the temporal lobe, and posterior horn (cornu posterius), directed into the occipital lobe. The region where the central part transitions into the posterior and inferior horns forms a dilatation known as the collateral trigone (trigonum collaterale). Important anatomical landmarks include corpus callosum (corpus callosum), which forms the roof of the anterior horn and central part, and fornix (fornix).
- Third ventricle (ventriculus tertius). This is an unpaired slit-like cavity wedged between the two halves of the diencephalon. It features characteristic recesses: anteriorly, above the optic chiasm, is the optic recess (recessus opticus); inferiorly, toward the pituitary gland, extends the infundibular recess (recessus infundibuli); and in the posterosuperior part lies the suprapineal recess (recessus suprapinealis). The pineal gland (corpus pineale) is adjacent to the posterior wall of the cavity.
- Fourth ventricle (ventriculus quartus). This is the cavity of the rhombencephalon, extending from the pons to the medulla oblongata.
Pathways of cerebrospinal fluid circulation
Cerebrospinal fluid (CSF) is produced primarily in the lateral ventricles, as well as in the third and fourth ventricles. Its outflow follows a strictly defined route:
- From the lateral ventricles, CSF flows into the cavity of the third ventricle via the paired interventricular foramina (also known as the foramina of Monro).
- From the third ventricle, the fluid flows through the midbrain via a narrow channel — the cerebral aqueduct (aqueductus cerebri, or aqueduct of Sylvius).
- Through the cerebral aqueduct, CSF enters the fourth ventricle.
- From the fourth ventricle, the fluid exits into the subarachnoid space through special apertures in the roof: the unpaired median aperture (apertura mediana, foramen of Magendie) and the paired lateral apertures (apertura lateralis, foramina of Luschka).
Properties of CSF and the blood-brain barrier
Normally, cerebrospinal fluid is completely transparent and colorless. It is important to understand that it is not a simple ultrafiltrate of blood plasma, but is actively produced by the choroid plexuses. The cell count is minimal: no more than 4 cells per 1 µL are found (up to 85% of these are lymphocytes). Protein levels are low, and glucose accounts for 50–60% of its blood concentration.
Between the blood of the plexus capillaries and the CSF lies the blood-brain barrier (BBB). Its histological structure includes vascular endothelium, basement membrane, and plexus epithelium. The BBB has selective permeability:
- Freely permeable to: water, oxygen (O₂), and carbon dioxide (CO₂).
- Relatively impermeable to: various electrolytes.
- Strictly impermeable to: blood cells.
CSF changes in CNS infections and tumors
Analysis of CSF obtained via lumbar puncture is of paramount diagnostic importance.
| Parameter | Normal | Purulent meningitis | Tuberculous meningitis |
|---|---|---|---|
| Appearance | Clear | Turbid | Yellowish (xanthochromic) |
| Pandy's test | Negative | Strongly positive (+++) | Strongly positive (+++) |
| Cells (per 1 µL) | ≤ 4 (lymphocytes) | Several thousand (neutrophils) | Up to 1500 (mononuclear cells) |
| Lactate (mmol/L) | < 2,1 | > 3,5 | — |
In viral meningitis, the CSF remains clear, Pandy's test is positive (+), thousands of mononuclear cells (including activated B-lymphocytes) are detected, and the lactate level is usually < 3.5 mmol/L.
In brain abscess, the fluid may become turbid, containing mononuclear cells or neutrophils; glucose levels drop, and localized IgA synthesis may be detected. In herpes simplex encephalitis, the CSF is colorless; mononuclear pleocytosis or a normal cell count is possible, but IgG, IgM, and IgA levels increase, and herpes simplex virus is detected by PCR.
Briefly: answers to topical questions
What anatomical structures form the walls of the third ventricle?
The third ventricle is an unpaired slit-like cavity of the diencephalon located between its two halves. Sources indicate that the pineal gland (corpus pineale) is adjacent to its posterior wall. The third ventricle features the optic recess (recessus opticus), infundibular recess (recessus infundibuli), and suprapineal recess (recessus suprapinealis).
What structures bound the anterior horn of the lateral ventricle?
The walls of the anterior horn of the lateral ventricle are formed by:
- Corpus callosum (corpus callosum) — forms the roof of the anterior horn.
- Head of the caudate nucleus (caput nuclei caudati) — forms the lateral wall of the anterior horn.
The anterior horn (cornu anterius) projects into the frontal lobe.
What anatomical formations form the floor of the fourth ventricle (rhomboid fossa)?
The floor of the fourth ventricle, or rhomboid fossa, is formed by the structures of the posterior surface of the pons and medulla oblongata. It features:
- Medial eminences (eminentiae mediales), located on both sides of the median sulcus.
- Facial colliculus (colliculus facialis) in the posterior part of the superior triangle.
- Sulcus limitans (sulcus limitans), laterally bounding the medial eminences.
- Locus coeruleus (locus coeruleus) in the upper parts of the sulcus limitans.
- Superior and inferior foveae (fovea rostralis and fovea caudalis), located along the sulcus limitans.
- Medullary striae, dividing the floor of the fourth ventricle into rostral and caudal parts.
- In the caudal part — the vagal trigone, hypoglossal trigone, and vestibular area.
On the sides, the rhomboid fossa is bordered by the superior and inferior cerebellar peduncles.
Class and exam questions
How does cerebrospinal fluid get from the lateral ventricles to the third ventricle?
Communication between these cavities occurs via the interventricular foramina, traditionally called the foramina of Monro.
What are the foramina of Magendie and Luschka?
These are the apertures in the roof of the fourth ventricle through which cerebrospinal fluid flows into the subarachnoid space. The foramen of Magendie is the unpaired median aperture, and the foramina of Luschka are the paired lateral apertures.
Is cerebrospinal fluid pressure equal to intracranial pressure?
No, the cerebrospinal fluid pressure (which is 70–120 mm H₂O in the supine position) does not correspond to the general intracranial pressure.
Does the albumin quotient depend on age?
Yes, this parameter varies normally: in children under 15 years old it is < 5, in adults under 40 years old it is < 7, and in individuals over 40 years old it is < 8.
What else to study on this topic
- The mechanism of active cerebrospinal fluid secretion by choroid plexus cells.
- Histological structure of the choroid plexus epithelium and blood-brain barrier capillaries.
- Biochemical criteria (lactate and albumin quotient) in the differential diagnosis of meningitis.
- Specific diagnosis of herpes encephalitis (role of PCR and immunoglobulin synthesis).
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