In renal artery stenosis assessment, which Doppler parameter measured at the renal hilum is the most reliable indirect sign of hemodynamically significant stenosis?
- A Peak systolic velocity (PSV) >180 cm/s at the stenosis
- B Tardus-parvus waveform with acceleration time >70 ms and acceleration index <3 m/s² ✓
- C Resistive index (RI) <0.5 in the main renal artery
- D Renal-aortic ratio >3.5
Correct answer: B. Tardus-parvus waveform with acceleration time >70 ms and acceleration index <3 m/s²
Explanation
The 'tardus-parvus' waveform (slow rise time, small amplitude) of segmental or interlobar arteries distal to a significant renal artery stenosis is the most reliable indirect Doppler sign. Acceleration time >70 ms and systolic acceleration index <3 m/s² indicate damping of the waveform due to high-grade proximal stenosis. Direct Doppler criteria (PSV >180-200 cm/s, renal-aortic ratio >3.5) assess the stenosis itself but are technically limited by body habitus and bowel gas. RI <0.5 is not a standard criterion for renal artery stenosis.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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