Anatomical Basis of Hydrocephalus Flashcards
Everything rostral to the foramen of Monro in the lateral ventricle is considered…
This is considered to be in which lobe of the brain?
Anterior (frontal) horn
frontal lobe
What is everything caudal to the foramen of monro but rostral to the atrium is considered what?
body of lateral ventricle
Everything caudal to the atrium of the lateral ventricle is considered the … and is in the … lobe of the brain
posterior (occipital) horn
occipital lobe
How are the lateral ventricles connected?
there is no direct connection between the two lateral ventricles
only continuity is via the Foramen of Monro (interventricular foramen) which opens into the midline third ventricle
What part of the lateral ventricle is smaller than the superior portion and does not extend as far rostrally?
inferior (temporal) horn
What is the most rostral midline ventricle?
third ventricle
Inferiorly, the third ventricle expands into what area?
hypothalamic region
What are the rostral and caudal borders (partially) of the third ventricle?
rostrally - anterior commissure
caudally - posterior commissure
As the third ventricle narrows dramatically in a caudal direction to become the Cerebral Aqueduct, where will the aqueduct course?
between the tectum and tegmentum of the midbrain and a portion of teh pons
The lateral walls of the third ventricle abut what structure?
medial surfaces of paired thalamuses
What is the central merging of two thalamuses called?
massa intermedia or thalamic adhesion
What structures does the midline fourth ventricle separate?
the caudal portion of the pons and rostral portion of the medulla from the ventral surface of the cerebellum
When the cerebral aqueduct dilates, this area becomes the fourth ventricle; it reaches maximum size at what point? What is this area called?
near the caudal end of the pons
fastigium
Where does the fourth ventricle terminate?
in the rostral portion of the medulla as the triangular Obex
What forms the lateral and superior borders of the fourth ventricle?
cerebellar peduncles
The caudal tip of the Obex is continuous with what structure?
central canal of the spinal cord
Just rostral to the obex, the roof of the fourth centricle is perforated forming what? Where does this lead?
Median Aperature (Foramen of Magendie)
leading into subarachnoid space
On the caudal end of the fastigium, the lateral wall of the fourth ventricle evaginates to form what? Where does this lead to?
Lateral Aperatures (Foramen of Luschka)
leading to subarachnoid space
What are the three major components that allow the functionality of the BBB?
- coupled, nonfenestrated endothelial cells (tight junctions)
- continuous basement membrane (with pericytes)
- astrocytes with their tube feet on the outside of the basement membrane
What is the primary site for secretion and chemical modification of CSF?
choroid plexus
Where is the choroid plexus?
mostly in lateral ventricles
some in dorsal 3v
some in fastigium of 4v
The choroid plexus is a specialized derivative of…
What are these structures sources of?
pia matter (vasculature source) and ependymal cells (lining epithelium)
What are the three layers of the choroid plexus and what is within each?
- fenestrated endothelial cells= capillaries
- stroma layer= discontinuous basment membrane around the capillaries, loose CT, immune cells
- simple cuboidal epithelium = derived from ependymal cells
the fenestrated endothelial cells of the choroid plexus that form the capillaries promote what?
movement out of the capillary
To increase surface area, the choroid plexus forms… and the epithelial cells have…
The epithelial cells have what kind of junctions to each other?
highly folded villi
microvilli
zona occludens and desmosomes
What cells are the biological filters for the production of CSF?
epithelial cells of the choriod plexus
What are the two cells of the ependyma?
Ependymal cells
Tanycytes
What is unique to true ependymal cells?
has both microvilli and cilia
What creates the barrier between CSF and neural tissue?
ependyma
What is the role of the tanycyte within the ependyma?
performs limited absorption and secretion of the CSF
they extend small cellular process through the basement membrane and make direct contact with the surrounding capillary
Perivascular tube feet of astrocytes appear to have specialized clefts that allow fluid and some material out of the periarterial space and into the interstitial tissue of the brain. These clefts can also function as a conduit for flow of interstitial fluid and waste out of the interstitial space and into the perivenous space. This is considered what system?
Glymphatic system
How is the activity level or flow rate of the glymphatic system regulated? When is it most active?
regulated by the activity level of the astrocytes
most active when the surrounding neural tissue is least active (sleeping)
The ‘depth’ of subarachnoid space is determined by the length of trabeculae deep to the arachnoid matter and superficial to pia matter. It is relatively small in most places except for these areas…
- Cisterns
- chiasmatic cistern
- interpeduncluar cistern
- pontine (pontomedullary) cistern
- cisterna magna (cerebellomedullary cistern)
- quadrageminal (superior) cistern
- lumbar cistern
Which is the largest of the CSF cisterns? Where is it?
cisterna magna
triangle between dorsal surface of medulla, inferior surface of cerebellum, inner surface of the occipital bone
The quadrageminal cistern surrounds what?
pineal gland
What cistern surrounds the cuada equina?
lumbar cistern
After the CSF leaves the fourth ventricle through either the lateral or median aperatures and heads toward subarachnoid area, where does it ultimately go?
lateral - along ventral surface of the brain to superior sagittal sinus
median - enter cisterna magna, then quadrigeminal cistern then along the superior surface of the tentorium cerebelli to approach the superior sagittal sinus
As CSF approaches the superior sagittal sinus, it can flow through evaginations of teh arachnoid matter through the deep (meningeal) layer of the Dura Matter. What are these evaginations called?
Arachnoid Granulations
Where are most of the arachnoid granulations?
mostly around the superior sagittal sinus which is between the periosteal and meningeal layers of teh dura matter
How does CSF get into blood?
in granulations, CSF is separated from the venous blood only by thin arachnoid membrane; pressure in CSF is greater than that of the venous pressure so CSF just flows into the blood
By submerging the brain in CSF, what is the effective weight of the brain?
45g
What is the volume of the subarachnoid space and ventricles?
What volume of CSF is produced daily?
Entire volume of CSF then, can be cycled how many times a day?
150 ml
500 ml
3-4x a day cycling
Rate of CSF cycling depends on what?
- vascular system
- vasodilation increases CSF release
- elevated venous pressure decreases CSF absorption
What is this hypothesis called:
Since the total volume is fixed, any increase in pressure or volume in one of the three contents of the skull must be compensated for by a decrease in one of the other two.
Monro-Kellie Hypothesis
Ultimately, CSF volume is dependent on what?
hydrostatic pressure
hypoventilation increases CSF volume (by decreasing peripheral arteriole resistance)
increased venous pressure reduces CSF absorption thereby increasing CSF volume
What is the normal range of ICP? What is the danger zone line?
7-15 mmHg is normal
>25 mmHg is a danger zone
CSF control of ICP can only cover what pressure change, roughly?
2 mmHg
The CSF system can typically accomodate how much of a volume increase?
100 ml
What are the two MCC of increased volume in the skull?
tumors and hematomas
What are three responses the brain may have to increased volume?
- compression of the brain
- less ventricles
- decrease CSF production
- pool in lumbar cistern
- midline shift
- herniation
- falx cerebri L/R
- cerebellum through foramen magnum
What are the MCC of non-communicating hydrocephalus?
- aqueductal stenosis (congenital or tumor)
- blockage of 4th ventricle (tumor in cerebellum)
MCC of Communicating hydrocephalus
- tumor within choroid plexus - dramatic increase CSF outflow
- disruption of CSF resorption - hematoma or dural scarring post-meningitis
60 yo with difficulty walking, cognitive impairment, and urinary incontinence
ventricular volumes increased
normal pressure hydrocephalus
How would you treat pressure related hydrocephalus?
inserting catheter/shunt into one of the lateral ventricles
