RVT Cerebrovascular Anatomy and Disease 2 — Questions and Answers
Question 1: Which vessel is most commonly responsible for a watershed infarct between the MCA and ACA territories?
- Internal carotid artery stenosis (Correct answer)
- Vertebral artery occlusion
- Posterior communicating artery aneurysm
- Basilar artery thrombosis
Correct answer: Internal carotid artery stenosis
Severe ICA stenosis reduces perfusion pressure, making the border-zone watershed region between MCA and ACA territories vulnerable to ischemia.
Question 2: On duplex ultrasound, a post-stenotic flow pattern distal to a high-grade ICA stenosis is characterized by:
- High-resistance monophasic waveform
- Tardus-parvus waveform with delayed systolic upstroke (Correct answer)
- Reversed diastolic flow
- Normal triphasic waveform
Correct answer: Tardus-parvus waveform with delayed systolic upstroke
Tardus-parvus (slow-rising, rounded systolic peak with reduced amplitude) waveform is the classic post-stenotic pattern seen distal to significant stenosis.
Question 3: The carotid siphon refers to the S-shaped segment of the internal carotid artery located in the:
- Neck at the carotid bifurcation
- Cavernous sinus within the skull base (Correct answer)
- Petrous temporal bone
- Parapharyngeal space
Correct answer: Cavernous sinus within the skull base
The carotid siphon is the S-shaped intracranial portion of the ICA that courses through the cavernous sinus.
Question 4: A patient with subclavian steal syndrome will demonstrate which finding on vertebral artery duplex?
- Antegrade high-velocity flow throughout systole and diastole
- Complete reversal of flow direction throughout the cardiac cycle (Correct answer)
- Monophasic low-resistance antegrade flow
- Absence of Doppler signal bilaterally
Correct answer: Complete reversal of flow direction throughout the cardiac cycle
Complete subclavian steal causes full reversal of vertebral artery flow as blood is 'stolen' retrograde to supply the ischemic subclavian artery territory.
Question 5: The normal intima-media thickness (IMT) of the common carotid artery in adults under 50 years is generally accepted as less than:
- 0.5 mm
- 0.9 mm (Correct answer)
- 1.2 mm
- 1.5 mm
Correct answer: 0.9 mm
An IMT of less than 0.9 mm is generally considered normal in adults, while values ≥1.0 mm suggest subclinical atherosclerosis.
Question 6: Which collateral pathway opens when the ipsilateral ICA is occluded and the contralateral ICA is patent?
- Anterior communicating artery (Correct answer)
- Posterior communicating artery
- Ophthalmic artery retrograde flow
- Basilar artery-to-MCA anastomosis
Correct answer: Anterior communicating artery
The anterior communicating artery connects the two ACAs, allowing contralateral ICA flow to supply the ipsilateral hemisphere via the ACoA.
Question 7: Fibromuscular dysplasia (FMD) of the internal carotid artery most commonly affects which segment?
- Proximal ICA just above the bifurcation
- Mid-cervical ICA (C1-C2 level) (Correct answer)
- Cavernous ICA siphon
- Petrous ICA
Correct answer: Mid-cervical ICA (C1-C2 level)
FMD most commonly affects the mid-cervical segment of the ICA at the C1-C2 vertebral level, producing the classic 'string of beads' appearance.
RVT Cerebrovascular Anatomy and Disease 2
Which vessel is most commonly responsible for a watershed infarct between the MCA and ACA territories?