Diagnostic Ultrasound - Abdomen and Pelvis

Transplant Renal Artery Stenosis
TERMINOLOGY
Abbreviations
• Transplant renal artery stenosis (TRAS)
Definitions
• Narrowing of the transplant renal artery (TRA)
IMAGING
General Features
• Best diagnostic clue
○ Focal elevation of peak systolic velocity (PSV) with poststenotic
turbulence
• Location
○ Most commonly at arterial anastomosis
○ Can occur anywhere along transplant artery or there may
be diffuse involvement
○ In iliac artery proximal to renal artery graft (pseudo
TRAS)
• Surgical anatomy
○ End of graft artery-to-side of external iliac artery most
common
– Performed in living donor and cadaveric grafts
○ Patch of donor aorta along with single or multiple renal
arteries anastomosed with recipient external iliac artery
– Cadaveric graft only
○ End of graft artery-to-end of internal iliac artery or
branch uncommon
– Living donor or cadaveric graft
Ultrasonographic Findings
• Grayscale ultrasound
○ Appearance usually normal
• Color Doppler
○ Color aliasing at area of stenosis
○ Soft tissue vibration adjacent to stenosis
• Spectral Doppler
○ Direct criteria: Elevated PSV in stenotic area > 250-300
cm/sec
– Wide range of PSV in normal graft arteries: 60-200
cm/sec
○ Renal artery to iliac PSV ratio > 1.8-3.5
○ Sensitivity 87-94%, specificity 86-100 for > 50% stenosis
○ Moderate to severe post-stenotic turbulence
○ Indirect criteria: tardus parvus intrarenal waveforms =
slow systolic upstroke and decreased peak velocity
– Quantified by acceleration index, acceleration time,
and resistive index (RI)
□ Prolonged systolic acceleration time > 0.1 s and
decreased acceleration index < 3 m/s²
□ Low RI < 0.5
– Acceleration index and acceleration time less specific
than PSV of main renal artery and should not be used
as signs of TRAS in isolation
– Note that sensitivity and specificity depend on specific
Doppler criteria
○ More proximal stenosis such as common iliac or external
iliac stenosis may cause tardus parvus in main renal artery
and intrarenal arteries
• Ideal screening modality
• Contrast-enhanced US
○ Fast and noninvasive evaluation of graft perfusion
○ Time for contrast arrival and rate of inflow correlate with
degree of stenosis
○ Use is not limited by renal function
Nuclear Medicine Findings
• Isotope renography: Lower sensitivity (75%( and specificity
(67%) for TRAS
• Prolonged tracer transit using MAG3
CT Findings
• CTA
○ Comprehensive vascular evaluation including iliac
arteries and aorta
○ 3-dimensional images with high spatial resolution, can be
rotated for optimal angle
○ Accurate, noninvasive
○ Limited by nephrotoxicity, streak artifact from metal
MR Findings
• MRA
○ Comprehensive vascular evaluation
○ 3-dimensional images which can be manipulated for
optimal angle
○ High sensitivity (67-100%) and high specificity (75-100%)
○ No radiation or nephrotoxic iodinated contrast agents
– However, limited by risk of nephrogenic systemic
fibrosis when renal function is abnormal
○ Artifacts from surgical clips and metal prostheses may
lead to overestimate of stenosis or nondiagnostic study
• Nonenhanced MRA techniques increasing in diagnostic
value and accuracy
○ For patients with abnormal glomerular filtration rate in
whom gadolinium based contrast agents are best
avoided
Angiographic Findings
• Catheter angiography is gold standard but is invasive with
potential complications
• Confirms stenosis (> 50% stenosis on angiography
considered significant)
• Pull back pressure gradient across stenosis > 10-20 mmHg
suggests significant stenosis
• Carbon dioxide angiography useful to limit amount of
iodinated contrast
• Endovascular intervention can be performed
Imaging Recommendations
• Best imaging tool
○ Color, power, spectral Doppler US is screening modality
for TRAS
• Protocol advice
○ Careful attention to Doppler angle to ensure accurate
PSV measurements
○ Optimization of pulse repetition frequency and gain is
essential
DIFFERENTIAL DIAGNOSIS
Abrupt Renal Artery Curves and Kinks
• Curves and kinks can elevate peak velocity without stenosis
Diagnoses: Kidney Transplant
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