Doppler ultrasound of a renal artery reveals a resistive index (RI) of 0.85 and a delayed systolic upstroke (parvus-tardus waveform). What is the most likely diagnosis?
- A Renal artery stenosis, proximal to the area sampled ✓
- B Renal vein thrombosis
- C Acute renal parenchymal disease
- D Normal variant high-resistance waveform
Correct answer: A. Renal artery stenosis, proximal to the area sampled
Explanation
The parvus-tardus waveform (low velocity, slow rise — parvus = small amplitude, tardus = delayed systolic peak) on Doppler ultrasound is the indirect Doppler sign of significant proximal renal artery stenosis. It results from damping of the arterial pulse wave distal to a tight stenosis. An acceleration time >70 ms and acceleration index <300 cm/s² support the diagnosis. Renal vein thrombosis increases RI with absent or reversed diastolic flow. Acute parenchymal disease elevates RI uniformly without the parvus-tardus pattern. Normal RI is 0.5–0.7.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.