DMST 293 (Vasc 2) - Intracranial Arteries

What is the most frequent use of TCD and TCDI?

Vasospasms

What is the cavernous ICA? What is it aka?

Parasellar portion (Prox Seg)

Genu portion (the bend)

Supraclinoid portion (distal Seg)

Aka carotid siphon

Where is the cervical ICA?

Carotid bifurcation to the carotid canal of the petrous portion of the temporal bone

Where is the petrous ICA?

Runs through the petrous portion of the temporal bone (not seen on U/S) it is right before the parasellar segment

Which arteries in the CoW carries the most blood flow?

MCA (80%)

Do CoW velocities increase or decrease with age?

Decrease

What is the most common pitfall of TCD?

Misidentification of vessels (non-imaging)

What is the difference between TCD and TDCI?

TCD: non-imaging

TCDI: duplex imaging

What is the assumed angle of insonation in TCD?

0 degrees

T/F: under normal circumstances there is detectable flow in every part of the CoW

False, undetectable in communicating arteries

What CoW vessel has the highest and lowest velocity?

Highest: MCA

Lowest: PCA

What velocity should the MCA not exceed?

Should be < 90cm/s

From a transtemporal approach, what vessel do you hit at a depth of 3-6cm with flow towards the probe?

MCA

From a transtemporal approach, what vessel do you hit at a depth of 5.5-6.5cm with bidirectional flow?

MCA/ACA

From a transtemporal approach, what vessel do you hit at a depth of 6-8cm with flow away from the probe?

ACA (A1)

From a transtemporal approach, what vessel do you hit at a depth of 6-7cm with flow towards the probe?

PCA (P1)

From a transtemporal approach, what vessel do you hit at a depth of 5.5-6.5cm with flow towards the probe?

TICA

How is a transorbital scan done?

Eye closed, probe medial, power reduced

From a transorbital approach, what vessel do you hit at a depth of 4-6cm with flow towards the probe?

OA

From a transorbital approach, what vessel do you hit at a depth of 5.5-8cm?

Carotid siphon

From a transorbital approach, what vessel of the siphon flows away from the probe?

Supraclinoid

From a transorbital approach, what vessel of the siphon has bidirectional flow?

Genu

From a transorbital approach, what vessel of the siphon flows towards the probe?

Parasellar

What is the sub-occipital window?

At the foramen magnum

From a suboccipital approach, what vessel is at a depth of 6-9cm and flow is away from the probe?

Vertebral

From a suboccipital approach, what vessel is at a depth of 8-12cm and flow is away from the probe?

Basilar

What is the first major branch of the ICA?

The ophthalmic artery

Which vessel divides P1/P2 of the PCA?

The PCoA

Which vessel divides A1/A2 of the ACA?

The ACoA

Where do the vertebral arteries arise from?

The subclavian arteries

Where do the vertebral arteries enter the skull?

At the foramen magnum

What anastomoses to create the basilar artery?

The vertebral arteries

What are the max depth and velocity of scanning from the submandibular window?

8cm, 30cm/s

What are the fastest to slowest velocity CoW arteries?

MCA, ACA, PCA, basilar, vertebral, communicating arteries

In what direction does the MCA course?

Laterally towards the temporal bone with lots of branches

In what direction do the A1 and A2 segments course?

A1: medically (to midbrain)

A2: anteriorly (to anterior brain)

How long is the basilar artery?

3cm

What does the basilar artery bifurcate into?

The two PCAs

What window would you use to scan the cavernous ICA and ophthalmic artery?

The transorbital window

What window would you use to scan the MCA/PCA/ACA?

The transtemporal window

What window would you use to scan the vertebral and basilar arteries?

The suboccipital window

If scanning from a transtemporal window and using an anterior angle, what vessels could you sample from?

MCA, ACA, ACoA

If scanning from a transtemporal window and using a posterior angle, what vessels could you sample from?

PCA, PCoA, Basilar

What is meant by the mean velocity?

The mean of the peak velocities over time

What is the Lindegaard Ratio?

Used in Transcrainal Doppler to assess if vasospasms are present in the anterior circulation

What is the sviri ratio?

Used to determine vasospasms in the posterior circulation

Collateralization is direct evidence of what?

Carotid artery disease

What are the 4 types of collateralizations that can occur within the CoW?

Crossover

External to internal

Posterior to anterior

Leptomeningeal (LMC)

Vertebrobasilar

What are some indications that crossover collateralization is occurring?

Retrograde flow in the ipsilateral ACA, increase velocities in the contralateral ACA

What must be present for a crossover collateralization to occur?

A patent ACoA

What are some indications that external to internal collateralization is occurring?

Retrograde flow within the ipsilateral ophthalmic artery (from flow from the ECA)

What are some indications that posterior to anterior collateralization is occurring?

Increased flow in the ipsilateral PCA (exceeds the MCA)

What are some indications that leptomeningeal collateralization is occurring?

Become active (usually inactive)

High velocities in the ACA and PCA

What are some indications that vertebrobasilar collateralization is occurring?

Basilar artery flow reduced or to and fro

What types of conditions can cause narrowing of the cerebral arteries?

Thromboembolic & atherosclerotic disease

Non-inflammatory conditions (eg FMD, dissection, moyamoya disease, radiation induced vasculopathy)

What are inflammatory conditions resulting in intracranial stenosis/occlusion?

Temporal arteritis

Meningitis

Toxin-related vasculitis

Sickle cell disease

What mean velocity indicates stenosis of the MCA?

100 or 120 cm/s

What mean velocity indicates stenosis of the ICA?

90 cm/s

What mean velocity indicates stenosis of the ACA?

> 90 cm/s

What mean velocity indicates stenosis of the PCA?

> 80 cm/s

What mean velocity indicates stenosis of the basilar and vertebral arteries?

110 cm/s

What causes intracerebral aneurysms?

Weakening of the structural proteins within the media

What is the most common site for intracranial aneurysms?

ACoA

Where do subarachnoid hemorrhages (SAH) occur?

Between the arachnoid and pia mater layers of the cerebrum

What usually precedes intracranial vasospasms?

SAH (sub arachnoid hemorrhage)

Between the arachnoid and pia mater layers

What are the symptoms of vasospasms?

Mild: asymptomatic

Severe: reduced blood perfusion, symptomatic ischemic deficit, confusion, decreased consciousness, stroke

How are vasospasms treated?

Oral nimodipine and induced hypertension

Ballon angioplasty

If the MCA velocity is >120cm/s, what is indicated?

Reaction to a documented SAH

If the MCA velocity is increasing by >20cm/s per day, what does this mean?

Poor prognosis

If the MCA velocity is >200cm/s, what is indicated?

Critical reduction in cerebral blood flow

What are the sounds of snap, chirp of moan indicative of on TCD?

Emboli

If >50HITS/MES over a 10 min period is heard on TCD, what is indicated?

Increased risk of stroke

When would a peripheral thromboembolus be able to make it to the brain?

With a PFO

What's a bubble test?

Checking for a PFO

Patient is injected with micro air bubbles, if the FO is closed, bubbles go to the lungs. If the FO is open, bubbles cause HITS in the MCA

What is a cerebral autoregulation (functional reserve testing/vasomotor reactivity test)?

Patients breathes different concentrations of O2 and CO2 (or hold their breath)

MCA is monitored, peripheral vascular beds should dilate in response to the hypoxia and the MCA flow should increase

What does it mean if there is no change in the peripheral beds with the cerebral autoregulation test?

The beds are already maximally dilated