Neurovascular Specialist (NVS): Carotid and Vertebral Duplex Interpretation
Core concepts
NVS questions blend anatomy, hemodynamics, and clinical correlation. Master the carotid bifurcation: common carotid divides into internal (low resistance, no branches in the neck) and external (higher resistance, branches). Know how to identify the ICA versus ECA by waveform, branch anatomy, and response to tapping the superficial temporal artery. Understand plaque characterization - echogenicity, surface regularity, ulceration - and how stenosis is graded by peak systolic velocity, end-diastolic velocity, and the ICA/CCA ratio. Be comfortable with vertebral flow, subclavian steal physiology, and the meaning of a damped or tardus-parvus waveform downstream of a severe lesion. Correlate findings with symptoms: amaurosis fugax, hemispheric TIA, and the difference between symptomatic and asymptomatic disease.
Traps
High-velocity questions often hinge on distinguishing near-occlusion (string sign) from critical stenosis: in near-occlusion velocities may fall because flow is minimal, so a low velocity does not exclude severe disease. Another trap is mislabeling the ECA as ICA when the waveform looks low resistance from collateral supply. Also watch for questions that ask about the contralateral side or about a tandem lesion.
Rule of thumb
A peak systolic velocity above about 125 cm/s with an ICA/CCA ratio above 2 supports a hemodynamically significant stenosis; rising end-diastolic velocity and spectral broadening track severity. When velocity is unexpectedly low but the waveform is damped distally, suspect near-occlusion and confirm with imaging.
Worked example
A patient with transient right-hand weakness has left ICA PSV 240 cm/s, EDV 110 cm/s, ratio 4.2, and plaque with an irregular surface. Interpretation: severe symptomatic stenosis with an unstable plaque - a high-risk combination that warrants urgent vascular evaluation, not watchful waiting.