Neuroscience 4: Ventricular System of the Brain
What are the 4 ventricles of the brain?
2 lateral ventricles, 3rd ventricle, & 4th ventricle
What is the rate of CSF production?
20-25 mL/hr or 500 mL/day
How much CSF is in the ventricles?
25 mL
What does an outline of the third ventricle reveal?
4 protrusions, called recesses
How many parts is each lateral ventricle divided into?
5
What are the 5 parts each lateral ventricle is divided into?
Anterior (or frontal) horn in the frontal lobe. Body in the frontal & parietal lobes. Posterior (occipital) horn projecting backward into the occipital lobe. Inferior (or temporal) horn curving down and forward into the temporal lobe. Atrium, or tigone, the region where the body and posterior and inferior horns meet.
What are the lateral ventricles?
C-shaped & course through all the lobes of the cerebral hemispheres in which they reside
What is the choroid plexus the course of?
CSF
What happens when CSF continues to be produced even if the path of its circulation is blocked?
CSF pressure rises, and ultimately the ventricles expand at the expense of the surrounding brain, creating hydrocephalus
What is the human brain suspended in?
CSF; partially floats in the skull cavity
What are some reasons for defects in reabsorption of CSF?
Congenital absence of arachnoid villi. Obstruction of the superior sagittal sinus - venous pressure increases and prevents CSF movement.
What can hydrocephalus result from?
Excess production of CSF. Blockage of CSF circulation. Deficiency in CSF reabsorption. Ex vacuo.
What increases in pseudo tumor cerebri?
ICP
What does the CSF function as?
a buffer to absorb stress transferred through the rigid skull (among many other things)
What do patients with pseudo tumor cerebri present with?
a headache, visual disturbances such as diplopia and sixth cranial nerve (abducens) palsy
What is the third ventricle?
a midline slit in the diencephalon
What is the fourth ventricle shaped like?
a tent, the peak protruding into the cerebellum
Where do the largest arachnoid granulations lie?
along the superior sagittal sinus
What is the choroid plexus formed by?
an evagination of the ependymal layer of cells containing arterioles, capillaries and venules
What happens in 50% of cases of normal pressure hydrocephalus?
an idiopathic intermittent increase in ICP occurs
What is the cause of both types of hydrocephalus?
an obstruction in the path of CSF circulation
How much CSF is within and around the brain and spinal cord?
approximately 150-200mL
What are arachnoid granulations (or arachnoid villi)?
are small protrusions of the arachnoid through the dura mater
Where does the third ventricle end anteriorly?
at the lamina terminalis (the adult remnant of the rostral end of the neural tube)
What happens to the lateral point of the floor of the fourth ventricle?
becomes a narrow tuber that proceeds anteriorly and curves around the brainstem
Where is the fourth ventricle situated?
between the cerebellum, and the pons and rostral medulla
Where is the 4th ventricle located?
between the pons and the medulla, and the cerebellum
What is the rate of production of CSF relatively independent of?
blood pressure and intra-ventricular pressure
Where is the CSF produced predominantly?
brain ventricles
How does the choroid plexus generate CSF?
by filtering blood
What so processes leading to the obstruction of the aqueduct do?
can block free circulation of CSF
What is the lateral border of the lateral ventricles?
caudate nucleus
What are the strands of highly convoluted and vascular membranous material that all 4 ventricles contain called?
choroid plexus
What is the presentation of normal pressure hydrocephalus?
classic triad of bladder incontinence, dementia, and ataxia (wet, wacky, wobbly)
What is the diagnosis of normal pressure hydrocephalus?
clinical signs, with CT/MRI showing ventriculomegaly
What are the 2 types of hydrocephalus?
communicating & non-communicating
What is the upper border of the lateral ventricles?
corpus callosum
How is the ependymal layer specialized in the choroid plexus?
cuboidal, secretory epithelium - choroid epithelium
What does normal pressure hydrocephalus result from?
decreased reabsorption of CSF at the arachnoid granulations
What age group do you see normal pressure hydrocephalus?
elderly
What is the median aperture?
foramen of Magendie
What are the 2 lateral apertures?
foramina of Luschka
Where does the CSF circulate unidirectionally?
from the ventricles to the subarachnoid space to the venous sinuses of the brain (epidural)
Where does the CSF circulate constantly?
from the ventricles to the surface of the brain and drains in the venous sinuses of the skull
What happens in hydrocephalus?
greater than normal production of CSF or defects in reabsorption of CSF
What are the symptoms of increased intracranial pressure?
headache, nausea/vomiting, papilledema (except in normal pressure hydrocephalus), changes in consciousness (from sleepiness to coma), brain herniation (uncle and/or cerebellar tonsils, resulting in life-threatening brain stem compression
What does the pathology due to disruption of CSF circulation cause?
hydrocephalus
Where is the 2 lateral ventricles located?
in each hemisphere
Where is there a band of choroid plexus?
in each lateral ventricle
Where does the optic recess lie inferiorly?
in front of the optic chasm at the base of the lamina terminalis
Where does the interventricular foramen lay?
in the anterior part of each wall of the third ventricle
Where is the central canal?
in the caudal medulla and spinal cord; usually not patent over much of its extent
Where is the 3rd ventricle located?
in the midbrain
Where does the tail of the caudate nucleus lie?
in the roof of the inferior horn
What is the portion of the roof of the fourth ventricle caudal to the peak?
inferior medullary velum
What crosses the (3rd) ventricle in most human brains?
interthalamic adhesion
What are the 3 communications between the ventricles?
interventricular foramina (of Monro) - communication between the lateral the third ventricle; the cerebral aqueduct (aqueduct of Sylvius); Foramina of Lushka and Magendie
Where do the arachnoid granulations protrude?
into the venous sinuses of the brain and allow CSF to exit the sub-arachnoid space and enter the blood stream
What happens to the pineal recess superiorly?
invades the stalk of the pineal gland
What happens to the choroid plexus with age?
it becomes calcified and the gloms can often be seem in x-ray studies
Where does the suprarenal recess lie?
just anterior to this stalk
What is the tubular prolongation of the fourth ventricle?
lateral recess of the fourth ventricle aka the foramen of Luschka
What is the route of CSF circulation?
lateral ventricles --> 3rd ventricle --> 4th ventricle --> subarachnoid space --> venous sinuses (cisterns)
Some CSF goes into the subarachnoid space around the spinal cord and then does what?
makes its way caudally to the lumbar cistern
What is the lateral wall of the third ventricle?
medial surface of the thalamus and hypothalamus, and part of the hypothalamus forms its floor
What are the remaining causes of normal pressure hydrocephalus?
meningitis, subarachnoid hemorrhage, and atherosclerosis.
What does the hippocampus form in regards to the borders of the lateral ventricles?
most of the floor and medial wall of the inferior horn
What does the body of the caudate nucleus form?
most of the lateral wall of the body of the ventricle
What are all 4 ventricles interconnected through?
narrow pipe-like openings
What happens to the third ventricle at the posterior end of the mammillary bodies?
narrows fairly abruptly to become the cerebral aqueduct (aqueduct of Sylvius)
What is psuedotumor cerebri associated with?
obesity, oral contraceptives
Is there an identified cause for psuedotumor cerebri?
often not
What do arachnoid granulations act as?
one-way valves
What do people with normal pressure hydrocephalus not have?
papilledema and headaches
What does the fenestrated endothelium in the choroid capillary allow?
plasma/fluid through but blocks cells
What disorder is 8-10 times more common in women?
psuedotumor cerebri
Describe the floor of the fourth ventricle.
relatively flat, and it narrows rostrally into the aqueduct and caudally into the central canal
What is the floor of the fourth ventricle sometimes referred to as?
rhomboid foss
What is the medial border of the lateral ventricles?
septum pellucidum
On the inner surface of cranial bones what are produced by arachnoid granulations?
small pits called granular fovea
What is the portion of the roof of the fourth ventricle rostral to the peak?
superior medullary velum
What does the menu of the corpus callous curve down to form?
the anterior wall of the anterior horn
What does the 3rd ventricle communicate with the 4th ventricle through?
the cerebral canal (the aqueduct of Sylvius)
What does the thalamus form in regards to the borders of the lateral ventricles?
the floor of the body of the ventricle posteriorly
What do the lateral ventricles communicate with each other and with the 3rd ventricle through?
the inter ventricular foramen (of Monroe)
What does the head of the caudate nucleus form?
the lateral wall of the anterior horn
What does the septum pellucidum form?
the medial wall of the body and anterior horn
Where does the CSF in the subarachnoid space not penetrate through?
the pia mater of the brain
What does the body of the corpus callosum form?
the roof of these parts of the ventricle
What does the fourth ventricle communicate with?
the subarachnoid cisterns
What do the 3 apertures in the 4th ventricle do?
the ventricular system communicates freely with subarachnoid space
Describe the roof of the third ventricle.
thin, membranous roof containing choroid plexus
How is most of the CSF returned to the venous system?
through arachnoid villi that penetrate the dural sleeves accompanying spinal nerve roots
From the 4t ventricle, where does the CSF move?
through its foramina up and over the cerebral hemispheres, through the arachnoid villi and into the superior sagittal sinus
Where does the choroid plexus of each lateral ventricle grow?
through the inter ventricular foramen forming part of its posterior wall
What can the cause the blockage of CSF in hydrocephalus?
tumors of the choroid plexus (papillomas)
What are the 4 cavities in the brain called?
ventricles
What are smaller arachnoid granulations called?
villi
Where is the choroid plexus call the glomus?
where it is enlarged in the region of the atrium
Do patients with psuedotumor cerebri have papilledema?
yes
