CH 4 Cranial Vascular: Anatomy and Physiology Flashcards
Vascular structure of the brain includes:
Carotid arteries, vertebral arteries, the circle of willis and the venous sinuses.
80% of blood supply from the carotid artery.
20% from vertebral artery.
cerebral arterial blood supply is predominantly directed to the basal ganglia at the early stages of development and then to the white matter later.
Internal carotid arteries (ICA) course along each side of the neck, bifurcate to form
the anterior (ACA) and middle cerebral arteries (MCA) at the medial end of the sylvian fissure.
The anterior cerebral arteries supply:
the medial cortex, the medial portions of the frontal lobes and the superior medial parietal lobes.
ACA is seen curving around the corpus callosum.
Pericallosal artery
is the terminal end of the ACA and arches around the genue of the corpus callosum and runs along the longitudinal fissure anterior to posterior.
Heubner’s artery
important branch of the ACA supplies the anteriomedial part of the head of the caudate nucleus.
*main nutrient vessel of the caudate
ACA and pericallosal arteries best seen
in mid-sagittal plane through the anterior fontanelle.
*power doppler is best for evaluating the ACA because it provides a more accurate image.
Direction of flow in anterior cerebral artery (ACA) when performing TCD
is away from transducer
TCD is done in children when
child with sickle cell
Middle cerebral arteries
largest and most terminal branches of the ICA and the longest branch which helps form the circle of willis. the MCA supply the majority of the cerebrum.
MCA runs
laterally in the sylvian fissure as a continuation of the intracranial ICA and carries 80% of blood flow to the cerebral hemispheres. supplies a major part of the basal ganglia and its branches and lateral surface of the cerebral hemispheres.
MCA visualized
*the one intracranial vessel that can be evaluated most accurately
is seen at the level of the cerebral peduncles running anteriolaterally toward the lateral edge of the orbits.
MCA branches
tree-like small branches that bring blood to entire lateral aspect of each cerebral hemisphere, including the areas of speech (brocas area)
*small branches M3 branches “stroke arteries” because damage to them can cause major disabilities including paralysis.
Transtemporal position for TCD
best approach to image MCA
window is parallel to MCA and the blood flow is seen flowing towards the transducer.
Medial and lateral branches of the MCA supply
the basal ganglia and thalamus and are very thin, thus more prone to hemorrhage.
Posterior cerebral arteries supply
the occipital lobe of the brain and inferior aspects of the temporal lobes, the midbrain and thalami
Anterior communicating artery (AcomA) and Posterior communicating artery (PcomA) arise from
ICA
Anterior communicating artery (AcomA)
joins the anterior cerebral arteries (aca) which are branches of the ICA of each hemisphere
Posterior communicating artery (PcomA)
joins the MCA’s to the posterior cerebral arteries, which are part of the basilar artery system. Runs from the posterior cerebral arteries(PCA) to ICA
ECA
supply face, high resistance
ICA
supply the brain along with the verts, which help to form the circle of willis. low resistance.
Circle of willis
brains own collateral pathway and decrease blood pressure in brain. Important role in the pressure equilibrium of the cerebral vasculature.
Circle of willis formed by
blood carried by 2 ICA’s and basilar system come together and redistributed by the ACA, MCA, and PCA, with 2 AcomA and 2 PcomA.
formed by the anterior comm. artery, 2 anterior cerebral arteries, 2 ICA’s, 2 posterior comm arteries and 2 posterior cerebral arteries.
Basilar and MCA supply the brain…
they are not considered part of the circle of willis
Vertebral arteries
enter through the foramen magnum into the brain. just inferior to pons they join to become the basilar artery
Basilar artery
give off to R and L posterior cerebral arteries at superior level of the pons.
It can be seen pulsating in the notch of the cerebral peduncles.
Chorodial arteries
arise from the basilar and ICA
*supply the choroid plexes.
damage to these arteries can affect the CSF production
cerebral bloodflow autoregulation
brainstem better at autoregulation
pressures ranging from 50mmHg - 160 mmHg
- the cerebral cortex suffers at low pressures.
- the cerebral vasculature dilates when oxygen content is reduced, but this is limited.
Venous drainage of brain
superficial and deep drainage through veins and venous sinuses.
veins in brain have thin walls and no valves.
cerebral veins
superficial and deep.
superficial lie on surface and drain into SSS and deep veins drain internal structures of the brain into the straight sinus.
Superior cerebral veins
drain the superior, lateral and medial surfaces of the brain and open into the SSS
Middle cerebral vein
runs along the lateral cerebral fissure and is *connected with the SSS and transverse sinus
Internal cerebral vein formed:
from choroid vein and terminal or thalmostriate vein.
Terminal vein runs..
between thalmus and caudate nucleus.
Choroid vein runs…
along the choroid plexus and receives blood from the corpus callosum.
Internal cerebral veins
are paired and fuse posterior to pineal gland to form the great cerebral vein (vein of galen) and then course posterior to empty into the straight sinus.
Great cerebral vein (vein of Galen) runs
superiorly and joins the inferior sagittal sinus to form the straight sinus.
Venous thrombosis of the internal cerebral vein
thought to be due to trauma, may be a cause of thalamic edema.
Dural venous sinuses
are superficial and large, composed of dura mater, and responsible for deep drainage of the brain.
blood is drained into the internal jugular vein via dural sinuses.
The most prominent sinus?
Superior sagittal sinus
Main sinuses of brain:
Superior sagittal sinus (SSS) Inferior sagittal sinus straight sinus (vein of galen) transverse sinus (R&L) occipital sinus
Superior sagittal sinus (SSS)
seen within the falx and exhibits low amplitude cardiac pulsations.
High amplitude saw-tooth pattern is abnormal and indicative of cardiac abnormalities
arachnoid granulations dump into SSS
too much pressure with scanning may compress SSS
Superior sagittal sinus (SSS) thrombosis should be considered in neonates with:
severe dehydration, sepsis, ECMO
Paired Transverse sinuses
large in size.
the R trv sinus is a continuation of the SSS and
L is a continuation of the straight sinus.
Inferior sagittal sinus
difficult to see, superimposed in the pericallosal artery
Joins the vein of galen to form the straight sinus.
Straight sinus
junction of the falx cerebri and the tentorium cerebelli.
Internal cerebral veins are paired and fuse to form the great cerebral vein (vein of galen) then joins the inferior sagittal sinus to form the straight sinus.
watershed areas
area of brain at the end of vascular distribution, distant from the circle of willis, where cerebral arteries meet and form anastamoses.
-tertiary brain area located peripheral to primary distribution area for the anterior, posterior, and middle cerebral arteries; it derives blood via the branches of all 3 cortical arteries (ant,post, mid)
because of the extreme ends, they are particularly vulnerable to ischemia and infarction in those who have circulation problems.
2 major areas of the brain that can be affected by an asphyxia event ant the resultant hypoxia/ischemia are:
cortical “watershed” areas, and the deep structures; the basal ganglia “germinal matrix”
Resistive Index (RI)
systolic velocity - diastolic velocity / systolic velocity
Pulsatility index (PI)
systolic velocity - diastolic velocity / mean velocity
time average mean velocity (TAMV)
average of the mean blood flow over a period of time
*mean blood flow velocity is the most informative predictor of cerebral blood flow.
Infants with hydrocephalus, doppler studdies of the ACA and MCA
with and without pressure on the fontanelle and a change in RI is a good predictor for the need for shunt placement.
compression of anterior fontanelle when examining the ACA results in little or no change in normal child. With hydrocephalus, compression of the fontanelle increases the intracranial pressure resulting in an increase in arterial pulsatility.
Increased vasoliatation
decreases cerebrovascular resistance
increased vasoconstriction
increases cerebrovascular resistance which decreases cerebral blood flow
increase in intracranial pressure results in
decrease in diastolic flow in the intracranial vessels. resitive indices correlate well with rising intracranial pressure.
stable ventriculomegaly should have _______ pulsatility (PI) and resistive indices (RI)
NORMAL pulsatility and resistive indices; an elevated RI may imply the need for shunt.
ventriculomegaly - normal intracranial pressure
hydocephalus- increased intracranial pressure
ECMO
exhibit an absence of intracranial arterial pulsation altogether due to being placed on non-pulsatile cardiopulmonary bypass after ligation of the R common carotid artery and jugular vein. venous drainage is also affected which puts the infant at higher risk of infarctions while being treated.
severe hypocarbia
lower than normal carbon dioxide levels in the blood, induced by hyperventilation can result in ischemia and PVL in preterm infants
changes in arterial carbon dioxide (CO2)
tension result in changes in cerebral blood flow.
with extreme elevations of CO2, a decrease in the cardiovascular resistance occurs along with transmural pressure in the capillaries of the brain and can lead to SEH.
Asphyxia results in
injury of cerebral autoregulation producing an increase in diastolic blood flow and a decrease in cerebrovascular resistance.
Cerebral edema
swelling after hypoxic- ischemic events, vessels compressed, and increased cerebrovascular resistance, with dampening of the diastolic blood flow.
TCD findings consistent with vasospasm following a sucharachnoid hemorrhage include
- greatly increased mean velocities in the cerebral arteries.
another finding in child with brain atrophy would be a low RI - asymmetric pulsations in the brain are the first indication of ischemia and potential unilateral cerebral infarction.
Increased RI seen in
intracranial bleeds, PVL, brain edema, subdural hematoma, hydrocephalus
Decreased RI seen in
asphyxia (decreased acutely), ECMO, AVM, brain atrophy, term infants
TCD in infants/children for:
AVM, hydrocephalus, subdural fluid, asphyxia, cerebral edema, brain death, and to asses for stroke prediction in sickle cell anemia.
4 natural cranial windows
transtemporal
transorbital
transforaminal
submandibular
transtemporal window
MCA, ACA, PCA, anterior and posterior communication arteries, and terminal portion of the ICA.
communicating arteries are only seen by TCD whern they are collateral routes.
MCA - towards transducer
MCA/ACA bifucation- bi directional; MCA towards, ACA away from transducer
PCA- circles around and shows flow towards
transorbital window
evaluate the ophthalmic artery and the 3 segments of the carotid siphon; parasellar genu and supraclinoid
transforaminal window
evaluate the intracranial portions of the basilar and verterbral arteries. direction from this window is away
submandibular window
evaluate extradural portion of the ICA. direction from this window is away.
relative flow velocities in the intracranial arteries :
MCA > ACA > PCA = BA = VA
most common AV malformation
vein of Galen aneurysm
Vein of Galen malformation
vascular irregularity characterized by a fistula between the cerebral arteries and the vein of Galen.
2 types of vein of galen aneurysm
- chorodial AVM - consist of multiple abnormal vessels in the midbrain with drainage into a dilated vein of Galen and the straight sinus.
- Infundibular AVM - one or more arterial feeders draining directly into the vein of Galen.
Vein of Galen malformation sono
cystic structure with arterial and venous flow within it is seen posterior to the foramen of Monro and superior to the 3rd vent.
Sub-axial fluid
CFD to determine between
subarachnoid vs subdural.
- subarachnoid space- lifts cortical vessels, vessels float
- subdural space- fluid pushes vessels towards brain surface, vessels compressed
Sickle cell anemia
hereditary, abnormal hemogloin in RBC. sickles or half-moon shaped, “stuck” in vessels, die sooner than healthy RBC causing anemia.
high velocities due to luminal narrowing. cerebral infarction due to vessel occlusion.
major complication- brain disease, “silent” strokes
TCD for Sickle cell anemia
screening tool to evaluate risk of stroke.
doppler MCA, ICA, ACA for an increase in mean flow velocity in children between 2-16 years.
TCD sickle cell anemia Mean flow velocities
- greater than 200 cm per second in the MCA, distal ICA, or ACA/MCA bifur ar indicative for high risk of stroke.
- drs treat pediatric patients with and increased flow velocity in the MCA with transfusions.
Factors influencing cerebral blood flow (CBF)
Age: CBF decreases with age
Hematocrit: decreased hematocrit= increased CBF
CO2: increased CO2 = increased CBF
Oxygen: hypoxia results in incresed CBF
Hypoglycemia: increases CBF = to get more glucose to the brain
Fever: CBF increases 10% for every increase in degree of the normal temperature
normal brain RI
.6-.8
HIE (hypoxic ischemis encephalopathy) RI
decreases RI = poor neuro outcome
brain edema due to HIE: RI
low TI initially
increased edema = increased RI
diastole may be reversed
