Doppler Ultrasound of the Renal Arteries
In an obese patient with uncontrolled hypertension and a right-sided flank bruit, Doppler ultrasound of the renal arteries is the most appropriate initial study to confirm renovascular hypertension. 1, 2
Clinical Rationale
The presence of a right-sided flank bruit is a key clinical finding that significantly increases the likelihood of renal artery stenosis, making renovascular hypertension the leading diagnostic consideration in this patient. 1 This physical examination finding, combined with uncontrolled hypertension in an obese patient not on medications, creates a classic presentation requiring vascular investigation. 1, 2
Why Doppler Ultrasound First
The American College of Radiology specifically recommends Doppler ultrasound as the initial screening modality for renovascular hypertension for several critical reasons: 1
- Can be performed regardless of renal function level (no contrast-related nephrotoxicity risk) 1
- No radiation exposure 1
- No requirement for contrast material 1
- Non-invasive and readily available 1
The diagnostic algorithm for renovascular hypertension involves initial screening with Doppler ultrasound to assess for renal artery stenosis, evaluate kidney size asymmetry, and measure resistive indices. 1
Subsequent Imaging if Needed
If ultrasound is positive or equivocal, proceed to CT angiography (assuming normal renal function) or MR angiography (if renal dysfunction but eGFR >30 mL/min) for definitive anatomic assessment. 1, 3 Conventional angiography is reserved for cases where intervention is planned and remains the gold standard for anatomic definition but is invasive. 1
Important Clinical Context
Renovascular hypertension is the most common type of secondary hypertension, accounting for 0.5-5% of all hypertensive patients. 1 The presence of a flank bruit suggests a vascular etiology that requires investigation, even in obese patients. 1 While obesity itself is a major risk factor for hypertension development and is associated with treatment failure 4, the flank bruit in this case points specifically toward a renovascular cause rather than obesity-related essential hypertension.
Critical Pitfall to Avoid
While CT angiography and MR angiography provide excellent anatomic detail, research shows they are not reproducible or sensitive enough to rule out renal artery stenosis as initial screening tools, with combined sensitivity of only 64% for CTA and 62% for MRA. 5 This supports the guideline recommendation to start with Doppler ultrasound as a screening test before proceeding to more advanced imaging. 1