Anatomic Basis of Hydrocephalus Flashcards
what is the foramen of monroe?
where is it located?
- the conduit between the lateral ventricles and 3rd ventricle
- insertion onto lateral ventricle divides the anterior horn from the body
- located in the frontal lobe
what is the atrium?
where is it located?
- the junction between the superior lateral ventricle (anterior horn, body and posterior horn) and the inferior lateral ventricle (inferior horn)
- its insertion on the superior lateral ventricle divides in the anterior horn and the body
the anterior horn of the ventricle is
- located in what lobe
- defined by what boundaries
- frontal lobe
- all of the temporal lobe rostral to the insertion of the foramen of monro
the body of the lateral ventricle is
- located in what lobe
- defined by what boundaries
- located in?
- defined as the lateral ventricle
- caudal to the foramen of monroe
- rostral to the atrium
the posterior lobe is
- located where
- defined by what boundaries
- in the occipital lobe
- defined as the lateral ventricle caudal to the atrium
the inferior horn of the lateral venticle is
- located where?
- defined by what boundaries?
- in the temporal lobe
- extends anteroinferioly from the atrium
describe the continuity of the lateral ventricles to one another
they are separated medially by the septum pellucidum (& have no direct connections), except briefly at the foramen of monroe / interventricular foramen
into what does the foramen of monroe empty?
the midline of the third ventricle
what is the most rostral midline ventricle?
the third ventricle
the 3rd ventricle are
- made of what components?
- bordered rostrally by?
- bordered caudally by?
- bordered medially by?
- components:
- inferior expansion - in the hypothalamus
- caudal extension - travels thru midbrain (between tectum & tegmentum) -> the pons -> dilates into 4th ventricle
- bordered:
- rostrally - by the anterior commissure
- posteriorly - by the posterior commisure
- medially - by the lateral walls of the thalami in the middle of the ventricle
the cerebral aqueduct
- travels how?
- forms what?
- in between the midbrain (separating tectum and tegmentum)
- expands into the 4th ventricle
what borders the 4th ventricle is bordered by
- ventrally?
- dorsally?
- superiorly?
- inferiorly?
- ventrally: caudal (superior) pons + rostral (superior) medulla
- dorsally: ventral surface of the cerebellum
- superiorly:dilation of cerebral aqueduct
- inferiorly: the central canal
what is the obex?
where is it located?
- triangular termination fo the 4th ventricle
- in line with the rotral medulla
what is the fastigium?
where is it located?
- the widest portion of the 4th aqueduct
- in line with the caudal end of pons
what are the aperatures of the brainstem?
where are they located?
what is their role?
- perforations of the 4th ventricle
- role: connects ventricular CSF to subarachnoid CSF
- locations:
- lateral aperature: just caudal to the end of the fastigium
- medial aperature: just rostral to the end of the obex
median aperature
- other name
- definition
- role
- location
- name: foramen of magendie
- definition: perforation of the 4th ventricle
- role: connects ventricular CSF to subarachnoid CSF
- location: just above to the end of the obex (termination of 4th ventricle in line with rostral medulla)
lateral aperature
- other name
- definition
- location
- role
- other name: foramen of luschka
- definition: perforation of the 4th ventricle
- connects ventricular CSF to subarachnoid CSF
- locations: just caudal to the fastigium (widest section of 4th ventricle, in line with caudal pons)
list & describe the layers that comprise the blood brain barrier
-
endothelial cells:
- NON-FENESTRATED
- connected by tight junctions
-
basement membrane:
- CONTINUOUS
- EMBEDDED WITH PERICYTES
- perivascular tube feet of astrocytes
how does fluid move across the blood brain barrier?
- there is minimal movement of fluid fom capillaries into blood
- this is due to the tight nature of the barrier, largely from
- non-fenestrated endothelium w/ tight junctions
- continuous basement membrane
what attaches to the outer basement membrane forming the blood brain barrier?
pericytes
the choroid plexus
- is derived from?
- is located where?
- has what role?
- derived from: pia mater & ependymal cells
- located: ventricles
- role: primary site of secretion of cerebrospinal fluid (CSF) from blood -> ventricles
in what direction does fluid move across the barrier surrounding the choroid plexus? why?
from blood (choroid plexus) -> CSF
higher hydrostatic pressure of blood
list & describe the layers that form the choroid plexus
- endothelial cells:
- FENESTRATED
- line with tight junctions
- basement membrane
- DISCONTINUOUS
- embedded within stroma: CT + immune cells
- epithelial cells (derived from ependymal cells)
- simple cuboidal
- have microvilli
- connected w/ zonula occludens & desmosomes
the ependyma
- has what role?
- is located where?
- location: lines the ventricles & surface of central canal
- role: provides a barrier against transfer between CSF and neural tissue
list & describe the layers that form the ependyma
list and describe the layers that form the ependyma
- epithelium:
- simple columnar
- have microvilli
- connected by zonula occludens & desmosomes
- made of epyndmal cells + tanycytes:
- ependymal cells: ciliated
- tanycytes: send projections in neural tissue vasculature
- basement membrane
- perivascular tube feet of astrocytes
what are tanycytes?
where are they found?
what is their role?
- definition: a type of epithelial cell
- location: found in the empyndema epithelium lining ventricles & central canal
- role: extend small cellular processes through the basement membrane to vessels in the surrounding nueural tissue, to perform limited absorption / secretion of CSF
the choroid plexus form what unique shape?
why is this important?
the form into villi
this allows for maximal surface area for CSF secetion
compare & constrast the endothelial cells of the
- BBB
- choroid plexus
- empendyma
- BBB: non-fenestrated w/ tight junctions
- choroid plexus: fenestrated w/ tight junctions
- ependyma: n/a
compare & contrast the basememt membranes of the
- BBB
- choroid plexus
- ependymal cells
- BBB:
- continuous
- contain pericytes
- lind with perivascular tube feet of astrocytes
- choroid plexus:
- discontinuous
- embedded in loose CT stroma
- ependymal cells
- pierced with tanycyte processes
- lined with perivascular tube feet of astrocytes
compare and contrast the epithelial linings of the
- BBB
- choroid plexus
- ependyma
- BBB - n/a
- choroid plexus & ependyma
- both:
- columnar with microvilli
- have demosomes & tight junctions
- derived from ependymal cells
- ependyma: ependymal cells (ciliated) + tanycytes (have foot processes)
- both:
where is the subarachnoid space?
between the pia mater and arachnoid mater
what determines the “depth” of the subarachnoid space?
why is this significant?
- the length of the fine trabeculae that connect the
- deep surface of subarabhnoid mater
- superficial surface of the pia mater
- this length throughout most of CNS is small - except at cisterns: deep subarachnoid spaces containing large amounts of CSF
what are the cisterns of the CNS?
where are they each located?
- chiasmatic cistern: surround the optic chiasms
- interpeduncular cistern: between cerebral peduncles + ventral space
- pontine cistern: around inferior pontine sulcus
-
cisterna magna (cerebellomedullary) cistern:
- posterior (dorsal) medulla
- inferior surface of cerebellum + inferior surface of occipital bone
-
quadrageminal (superior) cistern:
- immediately posterior (dorsal) to tectum + pineal gland
- along superior / inferior surfaces of tentorium cerebelli
-
lumbar cistern:
- inferior to L2 (conus medullaris)
- superior to S2 (end of dura mater)
once the CSF reaches the 4th ventricles, it can go to which major locations?
- through cantral canal of spinal cord -> pool in lumbar cistern.
- through the lateral aperature (just below fastigium) to the
- ventral surface
- superior sagittal sinus
- through the median aperature (just below opex)
- cisterna magna: dorsal medulla + inf cerebellum / occipital bone
- quadrigeminal cistern: dorsal to tectum & pineal gland + superior & inferior surface of tectorium cerebelli
- superior sagittal sinus
where is the pontine (pontomedullary cistern located?
around the inferior pontine sulcus
the cisterna magna
- has what other name?
- is formed by what borders?
- receives CSF how?
- cerebellomedullary cisterna
- borders:
- dorsal medulla
- inferior cerebellum
- inner occipital bone
- receives CSF from: median aperature
the quadrigminal cistern
- has what other name?
- is formed by what borders?
- receives CSF how?
- superior cistern
- borders
- superior tetorium cerebelli
- dorsal pineal gland
- dorsal tectum
- superior cerebellum / inferior tentorium cerebelli
- receives CSF via: cisterna magna
how does CSF get from the 4th ventricle to the superior sagittal sinus?
- two major routes:
- lateral aperature -> ventral space -> superior sagittal sinus
- median aperature -> cistern manga -> quadrigeminal cistern -> superior cistern
the lumbar cistern
- what significance?
- has what borders?
- receives CSF how?
- significance: contains the caunda equina
- borders:
- L2 - conus medullaris
- S2 - end of dura mater
- receives CSF via the central canal
arachnoid granules
- definition
- location
- makeup
- role
- definition: evaginations of arachnoid mater that protrude into dura matter
- location: in between the periosteal & meningeal dural layers speciifcally, which is where the _superior sagittal sinu_s courses
- makeup: only of thin arachnoid membrane
- role: delivers CSF from the cisterns into the superior sagittal sinus: i.e., major site of CNS absorption in the blood
how does CSF move across the CSF-blood barrier seen at the arachnoid granulations?
why?
- blood moves into the sagittal sinus
- pressure of the CSF > pressure of venous blood
how much does the adult brain weigh?
how does the presence of CSF change this?
1300 g
with CSF, the “effective” weight comes down to 45 g
what are the major sites of CSF production?
- choroid plexus
- pia matter arterioles
- deep to ependymal
how do changes in arterial and venous pressure alter CSF volume?
- arteries (choroid plexus): site of CSF secretion
- increased BP: increaes volume (increased secretion)
- decreased BP: decreased volume (decreased secretion)
- venous (sagittal venous sinus): site of CSF secretion
- increased BP: increases volume (less absorption)
- decreased BP: decreases volume (more absorption)
how does hypoventilation affect CSF volume?
why?
increases CSF volume
decreases peripheral vasculature resistance
what is the monro - killie hypothesis?
- that the skull is an elastic chamber filled with 3 compartments, and an increase in pressure / volume of one compartment results in a compensatory decrease in another
- blood
- brain
- CSF
the brain can accomodate for what changes of in intracanial volume up to what point? how?
increases beyond this point value result in what?
- can accomodate for changes up to 100 ml, via:
- decerasing CSF production (minor)
- shifting more CSF into the spinal cord -> lumbar cistern (major)
- beyond 100 mL will result in one of three alterations:
- brain compression: decreased ventricles
- midline shift: brain out of line with falx cerebri
- herniation: midline shift + herniation of cerebellum thru foramen magnum
what is hydrocephalus?
how does it generally present?
how is it treated?
- a marked increase in the volume of the ventricles
- generally, comes at the expense of the rest of the brain
- tx: inserting a catheter in the lateral ventricles
how does hydrocephalus present in newborns specifically?
- compensetory decrease in brain volumes (like with adults), +
- expansion of calvarial diameter
- expansion of the frontaneles
what are the two major classifications of hydrocephalus and what defines them?
- based on whether or not the CSF can leave the 4th ventricle into subarachnoid space
- communicating hydrocephalus: CSF can exit 4th ventricle
- non-communicating hydrocephalus CSF cannot exit 4th ventricle
what are the two major types of communicating hydrocephalus?
CSF movement from ventricle-subarachnoid space unimpeded
- choroid plexus tumor: increase in CSF output
- dural scarring / hematoma: decreased in CSF absorption
what are the two major types of non-communicating hydrocephalus?
movement of CSF from 4th ventricle to subarachoid space impeded
- aqueductal stenosis - congenital, tumor
- 4th ventricle blockage - m/c cerebellar tumor
normal pressure hydrocephaly
- demographics
- presentation
- findigns
- treatment
- demographics: 60 yr +
- presentation:
- gait impairment
- cognitive decline
- urinary incontinence
- findings: increased volume yet normal pressure
- imaging: ventricular increase + brain decrease
- lumbar spinal tap: normal CSF pressure
- treatment: nothing great; spinal tap = short term gait improvement
