B7.056 Prework: Brain Environs Flashcards
major skull hole
foramen magnum- location of medullary, spinal cord junction
skull fossae and the part of the brain within them
anterior fossa- inferior frontal lobe
middle fossa- inferior temporal lobes
posterior fossa- brainstem and cerebellum
layers of meninges
skull dura -outer leaflet adherent to periosteum of skull -inner leaflet forms tentorium and falx arachnoid pia -adherent to surface of brain -follows penetrating arteries to form perivascular space brain
meningeal spaces
epidural (between skull and dura)
subdural (between dura and arachnoid)
subarachnoid (between arachnoid and pain, contains CSF)
what are the tentorium and falx cerebri
sheets made of the inner leaflet of dura
falx
divides L and R hemispheres from top of brain to level of corpus callosum
tentorium
divides supra and infratentorial conpartments
components of supratentorial compartment
cerebral hemispheres
components of infratentorial compartment
cerebellum and brainstem
within posterior fossa
composition of normal CSF
125 ml clear, colorless pressure: 70-180 mm H2O 0-5 WBCs protein < 45 mg% glucose 50-75 mg%
function of CSF
shock absorber
provides some nutrients
removes some waste
structure of the ventricles
4 total
- 1 and 2 are lateral, C shaped and have an anterior, posterior, and inferior horn
- 1 and 2 connect with 3 via interventricular foramen
- 3 connects to 4 via cerebral aqueduct
extra-axial CSF spaces
contiguous with subarachnoid space over cerebral convexity
called cisterns
how is CSF produced
choroid plexus- specialized ependymal cells that produce an ultrafiltrate of plasma
located in ventricles
electrolyte comp similar to plasma
500 ml/ day produces
CSF circulation path
produces in ventricles
access to extra-axial space via median aperture (foramen of Magendie) and lateral apertures (foramen of Luschka) at medulla
percolate through subarachnoid space over cerebral convexities to arachnoid granulations
what causes CSF to flow
Pv»_space; Psas
created gradient to drive flow
absorption of CSF
via arachnoid granulations within major sinuses (sagittal and transverse)
one way bulk transport of CSF to venous system
sagittal sinus
along top of falx
transverse sinuses
at intersection of tentorium and skull
major vessels of venous drainage
sagittal sinus
straight (rectus sinus)
transverse sinus
internal jugular
meningeal lymphatics
located parallel to the dural sinuses and meningeal arteries
drain immune cells, small molecules, and excess fluid from the CNS into the deep cervical lymph nodes
blood brain barrier
tight junctions of brain capillaries endothelial cells limit transfer of molecules (esp ionized molecules)
blood CSF barrier
tight junctions of choroid endothelial cells limit transfer of molecules
significance of circumventricular organs
locations where BBB is interrupted
major circumventricular organs
pineal > melatonin release
neurohypophysis/median eminence > pituitary hormone release
area postrema > chemotactic trigger zone
4 types of herniation syndromes
- sub falcine
- central
- uncal
- tonsillar
sub falcine herniation
brain pushed under falx
ACA and RAS live here and are vulnerable
central herniation
compresses midbrain
sympathetic and parasympathetic fibers affected as visualized by pupils being midrange and nonreactive
uncal herniation
lateral mass puts pressure on CN III exit from midbrain
unilateral, dilated, nonreactive pupil
tonsillar herniation
life ending
compresses medulla
breathing and heart function impaired
broad classes of causes of meningitis
inflammation of the meninges
- infection
- neoplastic
- chemical
- autoimmune
symptoms and signs of meningitis
headache photophobia, sonophobia nausea nuchal rigidity encephalopathy cranial neuropathies ischemic stokes
acute bacterial meningitis CSF
100-5000 WBC (usually PMNs)
100-1000 protein
glucose < 40
chronic, aseptic meningitis CSF
10-300 WBC (usually lymphocytes)
protein 50-100
normal or reduced glucose
common causes of bacterial meningitis
listeria
h. flu
Neisseria
strep pneumo
ttx for bacterial meningitis
ampicillin
ceftriaxone
non communicating hydrocephalus
obstruction to flow intra-axial
4th ventricle not enlarged
communicating hydrocephalus
obstruction to flow extra-axial
4th ventricle enlarged
syndrome of hydrocephalus
gait problems
incontinence
cognitive issues
due to selective vulnerability of leg fibers, micturition center, and cingulum memory fibers near lateral ventricles
diagnosis of hydrocephalus
triad: gait problems, incontinence, cognitive problems supportive imaging lumbar puncture -opening pressure -meningitis?
normal pressure hydrocephalus
very chronic, communicating hydrocephalus
hydrocephalus ex vacuo
enlarged ventricles secondary to atrophy
no derangement in CSF flow
cortical sulci also enlarged
pseudotumor cerebri
idiopathic intracranial hypertension
etiologies of pseudotumor cerebri
poor absorption of CSF
rarely overproduction of CSF (choroid plexus papilloma)
venous sinus thrombosis
factors associated with pseudotumor cerebri
obesity
tetracycline
vit A
symptoms and signs of pseudotumor cerebri
slowly developing headache episodic blurred vision, vision loss double vision papilledema normal head imaging
treatment of pseudotumor cerebri
Diamox (decrease CSF production)
optic nerve fenestration
CSF shunt
indication / contraindication of LP in increased ICP
contraindicated with focal mass lesions (increased P in once compartment compared to another)
not contraindicated in patients with diffuse processes
head imaging needed to exclude mass lesion
causes of intracranial hypotension
post traumatic spontaneous -encephalocele -tarlov cyst -idiopathic
symptoms and signs of intracranial hypotension
orthostatic headaches
low opening pressure
treatment of intracranial hypotension
repair leak
blood patch
