What is the most appropriate study to confirm the diagnosis in an obese patient with uncontrolled hypertension (HTN) and a right-sided flank bruit, with no current medications or supplements?

Most Appropriate Diagnostic Study for Renovascular Hypertension

Doppler ultrasound of the kidneys (Answer B) is the most appropriate initial study to confirm renovascular hypertension in this obese patient with uncontrolled hypertension and a right-sided flank bruit.

Clinical Presentation Analysis

This patient presents with classic features suggesting renovascular hypertension as a secondary cause:

• Uncontrolled hypertension without current treatment 1
• Right-sided flank bruit on physical examination—a key clinical finding that significantly increases the likelihood of renal artery stenosis 1
• Obesity, which is associated with hypertension but the presence of a bruit suggests a secondary cause beyond obesity-related mechanisms 2, 3

The abdominal/flank bruit is specifically identified as a clinical feature associated with increased likelihood of renovascular hypertension 1. This physical finding, combined with severe hypertension, warrants investigation for renal artery stenosis 1.

Why Doppler Ultrasound is the Best Initial Study

Ultrasound with Doppler is the most appropriate first-line imaging modality for several compelling reasons:

• Can be performed regardless of renal function level, unlike contrast-enhanced studies 1
• No radiation exposure (RRL designation: B, meaning 0 effective dose) 1
• No contrast material required, avoiding risks of contrast-induced nephropathy or nephrogenic systemic fibrosis 1
• Cost-effective screening tool for renal artery stenosis 1
• Obesity is not an absolute contraindication, though it may reduce image quality 1

The ACR Appropriateness Criteria specifically recognize ultrasound as an acceptable modality for evaluating renovascular hypertension, particularly when contrast-enhanced studies are contraindicated or as an initial screening tool 1.

Why Other Options Are Less Appropriate

CT of Kidney (Option A)

• Requires iodinated contrast for CT angiography to visualize renal arteries adequately 1
• Radiation exposure (RRL ☢☢☢☢: 10-30 mSv effective dose) 1
• Risk of contrast-induced nephropathy, particularly if underlying renal dysfunction exists 1
• While CT angiography is highly effective for diagnosing renal artery stenosis, it should not be the first-line study when ultrasound can provide initial screening 1

Intravenous Pyelogram (Option C)

• Historically used but no longer recommended as a screening test for renal artery stenosis 1
• Inferior sensitivity and specificity compared to modern imaging modalities 1
• Requires contrast administration with associated risks 1
• This modality is "of historical note" and has been replaced by more effective imaging techniques 1

Plain Radiographs of Abdomen (Option D)

• Cannot visualize renal arteries or assess for stenosis 1
• No role in diagnosing renovascular hypertension 1
• May show kidney size discrepancies but provides no information about vascular anatomy 1

Diagnostic Algorithm for Renovascular Hypertension

Step 1: Initial Screening with Doppler Ultrasound 1

• Assess for renal artery stenosis
• Evaluate kidney size asymmetry
• Measure resistive indices

Step 2: If Ultrasound is Positive or Equivocal 1

• Proceed to CT angiography (if normal renal function) or MR angiography (if renal dysfunction but eGFR >30 mL/min) for definitive anatomic assessment
• Both modalities are highly effective for confirming renal artery stenosis 1

Step 3: Consider Conventional Angiography 1

• Reserved for cases where intervention is planned
• Remains the gold standard for anatomic definition but is invasive 1

Critical Clinical Considerations

Secondary Hypertension Screening

• Renovascular hypertension is the most common type of secondary hypertension, accounting for 0.5-5% of all hypertensive patients 1
• Prevalence increases to 25% in elderly dialysis patients and those with severe hypertension 1
• 20-40% of patients with malignant hypertension have secondary causes, making screening essential 4

Obesity-Specific Considerations

• While obesity is independently associated with hypertension through multiple mechanisms (insulin resistance, sodium retention, sympathetic activation, RAAS activation) 2, 3, the presence of a flank bruit suggests a vascular etiology that requires investigation 1
• Obesity may reduce ultrasound image quality, but this does not preclude its use as the initial screening modality 1

Common Pitfalls to Avoid

• Do not skip imaging based on obesity alone—the flank bruit is a specific finding that warrants investigation 1
• Do not proceed directly to CT angiography without considering ultrasound first, especially when renal function is unknown 1
• Do not use intravenous pyelography—this is an outdated modality with poor diagnostic accuracy 1
• Do not assume all hypertension in obesity is primary—secondary causes must be excluded when clinical features suggest them 5