ANA 303 Ventricular System Flashcards
What is the ventricular system?
a network of interconnected cavities and openings that produce and circulate CSF
What are the ventricles of the brain?
Left lateral ventricle
Right lateral ventricle
3rd ventricle
4th ventricle
Formamina connecting the ventricles and what they connect
- Interventricular foramina (Monro): lateral ventricles -> third ventricle
- Cerebral aqueduct (Sylvius): third ventricle -> fourth ventricle
- Median aperture (Magendie): fourth ventricle -> subarachnoid space
- Right & left lateral aperture (Luschka): fourth ventricle -> subarachnoid space
All ventricles embryologically originate from the________
Neural canal, forming early in the development of the neural tube.
The neural canal dilates within the prosencephalon, leading to the formation of the lateral ventricles and third ventricle.
The cavity of the mesencephalon forms the cerebral aqueduct. The dilation of the neural canal within the rhombencephalon forms the fourth ventricle
The forebrain/ prosencephalon forms the_________
telencephalon - lateral ventricle
diencephalon - 3rd ventricle
The midbrain/ mesencephalon forms the_________
cerebral aqueduct
The hindbrain/ rhombencephalon forms the_________
4th ventricle
The 4th ventricle continues with what?
Continues with the central canal of the spinal cord
The central canal of the spinal cord is lined by
Low columnar or cuboidal ependymal cells
Discuss the lateral ventricles
Found in the forebrain
Largest ventricle
Each communicates with the 3rd through interventricular foramen (MONRO)
Has different parts – a central body and 3 horns (corni)
The horns names arise from their positions in the different lobes
Describe the central part of the lateral ventricles
Roof: Under the surface of the corpus callosum
Floor: from lateral to medial side
- Body of caudate nucleus
- Stria terminalis & thalamostriate vein
- Upper surface of the thalamus (lateral part)
- Choroid plexus
- Upper surface of body of fornix
Medial wall:
-Septum pellucidum
Describe the horns of the lateral ventricles
THE ANTERIOR HORN is triangular and is situated in front of the IVF (Monro) and extends into the frontal lobe
THE POSTERIOR HORN lies behind the corpus callosum and extends into the occipital lobe. May be absent
THE INFERIOR HORN: largest of them all, and extends into the temporal lobe
What are the communications of the 4th ventricle
Communications
1. With the 3rd vent. Through?
Cerebral aqueduct.
- Inferiorly?
With the central canal of the medulla & spinal cord - Dorsally?
With median apperture (FORAMEN OF MAGENDI) - Laterally?
Aperture (FORAMEN OF LUSCHKA) communicates with subarachnoid space
Describe the 3rd ventricle
It’s a cavity in the diencephalon; a median between the 2 thalami
It is in the midline between the right and left ventricles
Anteriorly: hypothalamic structures – pineal, suprapineal,infundibular, and optic recess
Posteriorly: pineal recess and suprapineal recess
Roof: Ependymal cells
Floor: Hypothalamic structures - Optic chiasma, Tubercinerium, Pituitary stalk, Mamillary bodies, Posterior perforated substance and tegmentum
Describe the 4th ventricle
The last and lowest part of the ventricular system
Exists in the hindbrain
Diamond shaped when viewed superiorly and tent shaped when viewed laterally.
Situated b/w pons and medulla in front, and cerebellum behind.
Boundaries of the 4th ventricle
Inferolateral: gracile and cuneate tubercles, inferior cerebellar peduncle
Superolateral: superior cerebellar peduncle
Lateral recess
Roof and floor of the 4th ventricle
Roof
Upper Part: formed by superior cerebellar peduncle and superior medullary velum
Lower part: formed by inferior medullary velum and choroid plexus of 4th ventricle
Floor
Clinical Correlates of the ventricles
- Any obstruction in the system causes a dilatation superior to it
- Dilatation of both lateral ventricles - obstruction at 3rd ventricle
- Unilateral dilatation of the lateral ventricles - obstruction at IVF
- Disturbance of whole VS obstruction at F.Magendi and F. Luschka
Functions of choroid plexus
- Filters plasma from blood to create CSF
- Blood/CSF barrier
- Filter waste/ foreign substances from CSF
- Active ion transport in/out of CSF
Choroid Plexus Facts
- Typically 30CC of CSF is made per hour
- Approx 100-160CC CSF present in adult at one time
- CSF turns over about 3.7 times a day
What is CSF?
An ultrafiltrate of plasma that surrounds the brain and spinal cord
It is the fluid circulating in the ventricular system
Describe the cirulation of CSF
- CSF is produced by the choroid plexus of each ventricle
- CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord
- CSF flows through the subarachnoid space
- CSF is absorbed into the dural venous sinuese via the arachnoid villi
Functions of CSF
Buyancy
Protection
Excretion of waste products
Role in neurogenesis
Describe the role of CSF in neurogenesis
- CSF may contain growth factors and signalling molecules that promote the growth and survival of new brain cells
- CSF also helps maintain a healthy microenvironment for neurogenesis by regulating the pH, oxygen and glucose levels in the brain
- The mechanical movement of CSF through the brain can help stimulate the growth and proliferation of new neurons
Describe arachnoid granulations
Aracnoid granulations are like the workers at the end of the CSF production line, ensuring everything gets cleaned up and recycled efficiently
What is hydrocephalus and its occurs due to?
Hydrocephalus is a condition in which there is an abnormal accumulation of CSF in the brain due to a disturbance of flow or absorption, leading to an increase in the volume occupied by CSF in the CNS, causing increased intracranial pressure.
Hydrocephalus is characterised by head enlargement in infants.
The narrow space of the 3rd V. easily gets blocked by tumours leading to increased intracranial pressure in adults and hydrocephalus in children.
It can be due to to:
Excess production
Impaird reabsorption into bloodstream
Blockage in the ventricular system that causes CSF to accumulate
Symptoms of hydrocephalus
- Headache
- Blurred or double vision.
- Eye movements that are not usual.
- Enlargement of a toddler’s head.
- Sleepiness or sluggishness.
- Nausea or vomiting.
- Trouble with balance.
- Poor coordination.
Types of hydrocephalus
Communicating
Non-communicating/ obstructive
What is communicating hydrocephalus and the types?
Communicating (Non-obstructive) Hydrocephalus – Abnormal collection of CSF in the absence of any flow obstruction in the ventricles. Common causes usually involve the functional impairment of the arachnoid granulations, such as fibrosis of the subarachnoid space following a haemorrhage.
Types
Communicating without obstruction of CSF absorption
Normal pressure hydrocephalus, overproduction of CSF
Communicating with obstruction of CSF absorption
Subarachnoid hemorrhage (SAH)
Meningitis (bacterial and aseptic)
Leptomeningeal carcinomatosis
What is non-communicating hydrocephalus and what is its most common site of occurence?
(more common)
Non-communicating (Obstructive) Hydrocephalus – Abnormal collection of CSF, with flow obstructed within the ventricular system.
Obstruction at F. monro, aqueduct of sylvius or 4th ventricular outlet
What is chiari malformation?
In Arnold-Chiari malformation, the medulla and the tonsils of the cerebellum herniate through the foramen magnum and come to lie in the vertebral canal.
Apertures in the roof of the fourth ventricle are blocked (F.Magendi adn F. Luschka), leading to obstruction to flow of CSF and internal hydrocephalus.
Cranial nerves arising from the medulla are stretched. This is a congenital anomaly. It is often associated with syringomyelia.
Symptoms:
Dizziness
Balance problems
muscle weakness
numbness amd tingling in arms or legs
How does chiari malformation impair the venricular system?
-The herniation of the cerebellum into the spinal canal can cause a narrowing of the formen magnum, which can put pressure on the brainstem and block the flow of CSF
-This pressure can lead to a backup of CSF and in some cases, it can even cause a small tear in the dura mater, leading to a CSF leak
-CM is a fairly common cause of spontaneous CSF leaks, even without any trauma to the head or spine
What is Spina Bifida? Types
Nonfusion of the neural tube can be associated
with nonclosure or incomplete closure of the vertebral canal (spina bifida), leading to an opening in the spinal column, typically in the lower back. As a result of nonfusion of the neural tube neural tissue, such as the spinal cord and meninges, may lie outside the cranial cavity or vertebral canal.
Types include:
Myelomeningocele (most common and most dangerous)
Meningocele
Spina Bifida Occulta
Spina bifida occulta – the mildest form, is characterised by an incomplete closure of the vertebrae, without protrusion of the spinal cord. Most people with this form of spina bifida are unaware of having it, and its discovery is often incidental.
Meningocele (meningeal cyst) – where the meninges protrude between the vertebrae posteriorly, but the spinal cord is undamaged.
Myelomeningocele – the most severe form, where a portion of the spinal cord remains unfused and protrudes posteriorly through an opening in the vertebral canal, in a sac formed by the meninges. This is associated with severe disability
The opeining lesion in the spinla column causes CSF leakage which causes abnormalities in the shape and size of ventricles causing conditions such as chiarimalformation II or hydrocephalus
- The amount of CSF produced is lower than normal, which can cause a build up of CSF within the brain
- Flow of CSF can be impaired as SB acts as a ‘road block’for CSF
- These can lead to buildup of fluid, whichcan put pressure on the brain leading to hydrocephalus
Cause; inadequeste intake of folate/folic acid during pregnancy
symptoms:
1. weakness or total paralysis of the legs.
2. bowel incontinence and urinary incontinence.
3. loss of skin sensation in the legs and around the bottom – the child is unable to feel hot or cold, which can lead to accidental injury
What is a lumbar puncture?
Lumbar puncture is performed to obtain samples of cerebrospinal fluid (CSF) for various diagnostic and therapeutic purposes.
In this procedure, a needle is introduced into the subarachnoid space through the interval between the third and fourth lumbar vertebrae.
With the patient lying on his or her side, with the vertebral column well-flexed, the space between adjoining laminae in the lumbar region is increased to a maximum.
Taking full aseptic precautions, the lumbar puncture needle is inserted into the vertebral canal above or below the third lumbar spine.
An imaginary line joining the highest points on the iliac crests passes over the fourth lumbar spine and this is taken as a landmark to insert the spinal needle
What position is a lumbar puncture orchestrated in adult and children?
Therefore, a needle for lumbar puncture is
usually inserted between the third and fourth lumbar vertebrae (L3–L4) in the adult patient.
In children, the caudal end of the spinal cord is usually located at the third lumbar vertebra (L3). Therefore, the needle for lumbar puncture is inserted at the L4–L5 level in children (Fig. 3.2A).
How much CSF is withdrawn in a lumbar puncture?
Typically 5 to 15 mL of the CSF is removed during the lumbar puncture to perform the
cell count, protein analysis, and microbiological studies.
Treatment of Hydrocephalus
Occasionally, shunting procedures allowing
the CSF to drain into the peritoneal cavity or the bloodstream are helpful if performed early in the course of this
condition.
Ventriculoperitoneal shunt
Discuss a subclavian steal
Caused by retrogade blood flow in the vertebral artery due to proximal stenosis (narrowing) and or occlusion of the subclavian artery (due to atherosclerosis). This flow reversal is known as subclavian steal
The arm may be supplied by blood flowing in the retrogade direction down the vertebral artery at the expense of the vertebrobasilar circulation possibly depriving blood flow to the brain.
Signs and symptoms
syncope: fainting
presyncope: sensation that one is about to faint
neurologic deficits
severe memory problems
pins and needles in arms
