IS Case 85: Transplant Renal Artery Stenosis
Imaging Sciences URMC
Publication Date: 2009-05-20
Doppler waveforms of the transplant renal artery show elevated peak systolic velocity (PSV) at the anastomosis > 600 cm/s (Fig. 1). Comparison with the corresponding iliac artery shows a much lower velocity of about 200 cm/s (Fig. 2). Axial GRE centered at the RLQ renal allograft shows significant stenosis at the arterial anastomosis (Fig. 3). A coronal MIP from contrast-enhanced MRA again shows a high-grade stenosis (Fig. 4). Digital subtraction angiography shows the corresponding stenosis, similar in appearance to the MRA (Fig. 5).
Transplant renal artery stenosis (TRAS) is a treatable cause of post-transplant hypertension and allograft dysfunction. It typically occurs several months to a few years after transplantation. Stenoses occurring early are usually related to trauma of the donor or recipient vessels, whereas stenoses occurring late are often the result of athersclerotic disease. TRAS usually occurs at or near the surgical anastomosis, however it may occasionally occur in multiple different sites or the whole artery. The differential diagnosis from a clinical standpoint includes chronic graft rejection, hypertension maintained by the native kidneys, segmental infarction or thrombosed graft polar arteries.
In addition to laboratory tests, non-invasive imaging procedures including scintigraphy, ultrasound, and MRA/CTA are helpful in the evaluation of TRAS. Scintigraphy has been replaced by color Doppler sonography due to better sensitivity and specificity. Peak systolic velocity (PSV) and resistive index (RI) are used in the assessment of TRAS. RI is calculated by (S-D)/S where S and D are systolic and diastolic velocities, respectively. Evaluation of the RI is most useful in the post-stenotic vessels. A hemodynamically significant stenosis is considered if the PSV > 180 cm/s and RI > 0.5. Also if the PSV is significantly elevated compared the the prestenotic or iliac artery, then this is considered hemodynamically significant. MRA/CTA both have excellent sensitivity and specificity. However in patients with worsening renal function, the risk/benefit ration must be consider regarding the use of Gadolinium, however MR techniques are available without the use of Gadolinium. CTA suffers from potential nephrotoxicity and involves ionizing radiation. Conventional angiography is considered the gold standard for evaluation of TRAS and allows for therapeutic intervention.
Treatment of TRAS consists of conservative measures or angioplasty and stenting. If renal function is stable and Doppler parameters exclude a hemodynamically significant stenosis, treatment with an ACE inhibitor can be used to control blood pressure as long as serum creatinine and potassium are followed. Angiography with angioplasty and stenting should be considered for uncontrollable BP, worsening renal function or progression of stenosis by non-invasive procedures. In this case a 5 mm balloon angioplasty was performed, with normalization of the patient's renal function.
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