Topography and Relations of the Ventricular System
The ventricular system consists of 4 ventricles with an aqueduct connecting the 3rd and 4th ventricles. Cerebrospinal fluid (CSF) flows through the ventricles before entering the subarachnoid space of the brain and spinal cord from the 4th ventricle:
- Lateral ventricles:
- Contained in the frontal and parietal lobes
- Extends from the interventricular foramen of Monro to the splenium of the corpus callosum
- Anterior horn: in the frontal lobe
- Posterior horn: curves posteromedially into the occipital lobe
- Inferior horn:
- Largest compartment of the lateral ventricle
- Extends forward into the temporal lobe
- 3rd ventricle:
- A midline, slit-like cavity
- Derived from the primitive forebrain vesicle
- Cerebral aqueduct (of Sylvius):
- Small tube extending throughout the dorsal quarter of the midbrain
- Surrounded by periaqueductal gray
- Connects the 3rd and 4th ventricles
- 4th ventricle:
- Between the brainstem and the cerebellum
- The foramen of Luschka (lateral aperture) and the foramen of Magendie (median aperture) allow newly produced CSF to enter the subarachnoid space.
- Circumventricular organs:
- Structures characterized by extensive, highly permeable capillaries
- Surround the 3rd and 4th ventricles
- Regions do not typically contain a blood-brain barrier, which allows for communication between the peripheral blood and the CSF.
Choroid Plexus and Cerebrospinal Fluid
- Vascular pia mater in all ventricles
- Roof of the temporal horns of the lateral ventricles
- Floor of the body of the lateral ventricles
- Foramen of Monro
- Roof of the 3rd ventricle
- Medullary of the 4th ventricle, extending through the foramen of Luschka
- Actively secretes CSF in the lateral, 3rd, and 4th ventricles
- Clear, colorless liquid containing a small amount of protein
- Provides buoyancy and protection for the brain
- Regulates chemical concentration of neurotransmitters and metabolic waste
Subarachnoid Space and Circulation of Cerebrospinal Fluid
- Between the arachnoid and the pia mater
- Contains CSF, larger arteries and veins, and intracranial and intervertebral portions of the cranial and spinal nerves
Circulation of cerebrospinal fluid
- After production in the ventricles, CSF flows into the subarachnoid space.
- CSF flows freely within the subarachnoid space of the brain and spinal cord.
- CSF is reabsorbed by arachnoid granulations into the venous circulation.
- Hydrocephalus: a potentially life-threatening condition caused by the excess accumulation of CSF within the ventricular system. The clinical presentation is nonspecific and may include headache, behavioral changes, developmental delays, or nausea and vomiting. Diagnosis is confirmed with neuroimaging (ultrasound, head CT, or MRI) showing ventriculomegaly. Treatment is placement of a CSF shunt.
- Normal pressure hydrocephalus (NPH): enlargement of the ventricles without detectable elevations in intracranial pressure. Normal pressure hydrocephalus occurs most commonly in adults > 60 years of age. Symptoms include a triad of urinary incontinence, ataxia, and cognitive dysfunction and may be remembered by the mnemonic “wet, wobbly, and wacky.”
- Chronic microvascular ischemic disease: chronic atherosclerotic disease typically resulting in hypoperfusion to symmetric areas of the cerebral cortex and causing cerebral atrophy or other brain malformations. Unlike hydrocephalus, the intracranial pressure is not elevated.
- Chiari malformations (CM): a group of disorders defined by structural deficits in the brain and spinal cord leading to limited space in the posterior fossa and forcing cerebellar structures to protrude through the foramen magnum. Type II Chiari malformations are seen in combination with herniation of the cerebellar vermis, the brainstem, and the 4th ventricle into the foramen magnum. An association exists with myelomeningocele and multiple brain anomalies, including hydrocephalus and syringomyelia.
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