Most Appropriate Diagnostic Study
B. Ultrasound (Doppler ultrasound) of the kidney is the most appropriate initial study to confirm renovascular hypertension in this obese patient with uncontrolled HTN and a right-sided flank bruit. 1
Rationale for Doppler Ultrasound as First-Line
The American College of Radiology explicitly recommends Doppler ultrasound as the initial screening modality for renovascular hypertension because it 1:
- Can be performed regardless of renal function level
- Involves no radiation exposure
- Requires no contrast material (particularly important given obesity and potential renal dysfunction)
- Assesses renal artery stenosis, kidney size asymmetry, and resistive indices
The presence of a right-sided flank bruit is a key clinical finding that significantly increases the likelihood of renal artery stenosis, making this patient an ideal candidate for renovascular hypertension screening 1, 2. The bruit was strongly associated with renal artery stenosis in prospective studies (P < 0.0005) 2.
Diagnostic Algorithm Following Initial Ultrasound
If the Doppler ultrasound is positive or equivocal, the next step depends on renal function 1:
- CT angiography if normal renal function exists (provides definitive anatomic assessment)
- MR angiography if renal dysfunction is present but eGFR >30 mL/min
- Conventional angiography is reserved only when intervention is planned, as it remains the gold standard for anatomic definition but is invasive
Why Other Options Are Less Appropriate
CT of kidney (Option A) would be a reasonable second-line study after ultrasound if renal function is normal, but it is not the initial screening test of choice 1.
Intravenous pyelogram (Option C) is outdated and has been replaced by more sensitive modalities. Historical guidelines from 1993 noted that simple radionuclide scintirenography offered sensitivity and specificity not different from intravenous urography, but ACE inhibitor-enhanced studies have since superseded both 3.
Plain radiographs of the abdomen (Option D) provide no useful information for diagnosing renovascular hypertension and would be inappropriate 1.
Clinical Context Supporting This Diagnosis
This patient's presentation is classic for renovascular hypertension 1:
- Uncontrolled hypertension despite no current treatment (suggesting severe disease)
- Obesity (associated with resistant hypertension and secondary causes)
- Right-sided flank bruit (highly specific finding)
- Young enough presentation to warrant secondary cause investigation
Renovascular hypertension accounts for 0.5-5% of all hypertensive patients, with prevalence increasing to 25% in those with severe hypertension 1. The flank bruit suggests a vascular etiology that requires investigation, even in obese patients 1.
Important Caveat
While a bruit is highly associated with renal artery stenosis, rare cases exist where the audible bruit arises from an artery not contributing to hypertension, while the stenotic artery causing hypertension remains silent 4. This underscores the importance of comprehensive bilateral imaging with Doppler ultrasound rather than relying solely on the side of the bruit.