RVT Cerebrovascular Anatomy and Disease 3 — Questions and Answers
Question 1: When using the NASCET criteria to measure ICA stenosis, the denominator (reference vessel) is the:
- Common carotid artery diameter
- Bulb diameter at its widest point
- Distal ICA beyond the stenosis and bulb (Correct answer)
- External carotid artery diameter
Correct answer: Distal ICA beyond the stenosis and bulb
NASCET measures stenosis as (1 - stenotic lumen / distal normal ICA lumen) × 100%, using the distal ICA as the reference.
Question 2: A 'string sign' seen on duplex ultrasound of the ICA most likely represents:
- Near-total occlusion with a thin residual lumen (Correct answer)
- Normal low-flow state in a fasting patient
- Arteriovenous fistula
- Carotid body tumor compressing the vessel
Correct answer: Near-total occlusion with a thin residual lumen
The string sign describes a thin trickle of flow through a near-totally occluded ICA, distinguishing it from complete occlusion.
Question 3: Which Doppler waveform characteristic differentiates the external carotid artery from the internal carotid artery?
- ECA has low-resistance continuous diastolic flow; ICA has none
- ECA has high-resistance pulsatile flow with little or no diastolic flow; ICA has continuous low-resistance flow (Correct answer)
- ECA shows bidirectional flow; ICA shows monodirectional flow
- ECA has higher peak systolic velocity than ICA in all individuals
Correct answer: ECA has high-resistance pulsatile flow with little or no diastolic flow; ICA has continuous low-resistance flow
The ECA supplies high-resistance muscle and skin beds, producing a pulsatile waveform with minimal diastole, while the ICA supplies the low-resistance brain with continuous diastolic flow.
Question 4: A patient presents with transient monocular blindness (amaurosis fugax). Which artery is the most likely source of the embolic event?
- Vertebral artery
- Internal carotid artery ipsilateral to the affected eye (Correct answer)
- Basilar artery
- Posterior cerebral artery
Correct answer: Internal carotid artery ipsilateral to the affected eye
Amaurosis fugax is caused by emboli from the ipsilateral ICA traveling into the ophthalmic artery and its branch, the central retinal artery.
Question 5: The vertebral arteries typically originate from which vessels?
- Common carotid arteries
- Subclavian arteries (Correct answer)
- Brachiocephalic trunk bilaterally
- Aortic arch directly
Correct answer: Subclavian arteries
The vertebral arteries arise from the subclavian arteries bilaterally and ascend through the transverse foramina of C6 to C1.
Question 6: During transcranial Doppler (TCD) monitoring, a high-intensity transient signal (HITS) most likely represents:
- Venous air embolism from deep breathing
- Circulating microemboli (gaseous or particulate) (Correct answer)
- Artifact from patient movement
- Normal turbulent flow at the MCA bifurcation
Correct answer: Circulating microemboli (gaseous or particulate)
HITS detected during TCD monitoring represent microemboli (air or solid particles) passing through the insonated vessel and are a marker of embolic risk.
Question 7: Which condition is most associated with spontaneous carotid artery dissection in young patients without atherosclerotic risk factors?
- Hypertensive emergency
- Fibromuscular dysplasia (Correct answer)
- Diabetes mellitus type 2
- Hyperlipidemia
Correct answer: Fibromuscular dysplasia
FMD weakens the arterial wall media, predisposing young patients to spontaneous dissection of the ICA or vertebral artery.
RVT Cerebrovascular Anatomy and Disease 3
When using the NASCET criteria to measure ICA stenosis, the denominator (reference vessel) is the: