What is the most appropriate imaging modality for an elderly patient with hypertension and a right flank bruit (abnormal sound heard over the artery with a stethoscope)?

Imaging for Suspected Renovascular Hypertension in an Elderly Patient with Flank Bruit

The most appropriate initial imaging is kidney ultrasound with Duplex Doppler (Option A). 1

Rationale for This Recommendation

This elderly patient presents with classic clinical features suggesting renovascular hypertension: new-onset hypertension after age 50 and an abdominal/flank bruit. 1 These findings warrant investigation for renal artery stenosis (RAS), which in elderly patients is most commonly caused by atherosclerotic disease (90% of cases). 1

Why Duplex Doppler Ultrasound is Preferred

Duplex Doppler ultrasound is the optimal initial screening test because:

• No contrast requirement: Can be used regardless of renal function status, avoiding risks of contrast-induced nephropathy or nephrogenic systemic fibrosis 1
• Non-invasive and safe: No radiation exposure, making it ideal for initial screening 1
• High diagnostic accuracy: Sensitivity of 73-91% and specificity of 75-96% for detecting significant stenosis (>60%) when using peak systolic velocity (PSV) thresholds of 200 cm/s 1
• Cost-effective: Less expensive than CT or MRI for initial evaluation 1

Key Ultrasound Parameters

The two most important Doppler parameters are: 1

• Peak systolic velocity (PSV): Threshold of 200-300 cm/s indicates significant stenosis
• Renal artery to aortic ratio (RAR): Improves specificity by accounting for baseline hypertension

Why NOT CT or IV Pyelogram

CT angiography (Option B), while highly accurate (sensitivity 95-100%, specificity 92%), should be reserved for patients with normal renal function or when ultrasound is technically inadequate or inconclusive. 1 In this elderly patient with unknown baseline renal function, contrast exposure carries unnecessary risk. 1

IV pyelogram (Option C) is obsolete and no longer used as a screening test for renovascular hypertension. 1 This modality has been replaced by modern cross-sectional imaging techniques.

Clinical Algorithm

Step 1: Perform Duplex Doppler ultrasound as initial screening 1

Step 2: If ultrasound is:

• Positive or equivocal: Proceed to CT angiography (if eGFR >30 mL/min/1.73 m²) or MR angiography (if eGFR <30 mL/min/1.73 m²) for confirmation 1
• Negative with high clinical suspicion: Consider alternative imaging (CTA/MRA) 1
• Technically inadequate: Proceed directly to CTA or MRA based on renal function 1

Step 3: Reserve conventional angiography for intervention planning, not initial diagnosis 1

Important Caveats

Common pitfalls with ultrasound include: 1

• Operator dependence: Requires experienced sonographer
• Technical limitations: Obesity, bowel gas, or accessory renal arteries may limit visualization
• Velocity artifacts: May overestimate stenosis with contralateral disease or underestimate with critical stenosis

Before any contrast imaging, assess renal function with serum creatinine and eGFR calculation. 1 For patients with eGFR <30 mL/min/1.73 m², unenhanced MRA techniques should be considered to avoid nephrogenic systemic fibrosis risk. 1

The presence of a flank bruit increases the pretest probability of RAS significantly, making imaging investigation appropriate in this case. 1 However, the ultimate goal is identifying patients who will benefit from intervention (angioplasty or stenting), not just anatomic stenosis detection. 1