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E2298. Renal Transplant: Imaging Evaluation of the Main Complications During the Graft's Lifespan
Authors
  1. Jacqueline Franco; Universidad Autonoma De San Luis Potosi
  2. Daniel Sandoval; Universidad Autonoma De San Luis Potosi
  3. Alberto Gudiño; Universidad Autonoma De San Luis Potosi
  4. Carlos Romero Alaffita; Universidad Autonoma De San Luis Potosi
Background
According to the Global Observatory on Donation and Transplantation, kidneys are most frequent transplanted organs. In 2017 there was 90,306 kidney transplants all over the world, approximately 17% of kidneys transplanted fail in a period of 3 years. Renal transplant complications can be classified as early, intermediate, and late, depending on the time frame in which they occur. Surveillance imaging are routinely performed during the first 1–2 years after transplant for detection of acute rejection and chronic allograft nephropathy, which may be clinically occult.

Educational Goals / Teaching Points
To establish the epidemiology of kidney transplantation / Determine the most common renal transplant disorders by their time of presentation and physiopathology / Illustrate the main imaging findings in different pathologies of renal transplant, and the main principal differences between them.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Ultrasound findings of parenchymal abnormalities may be subtle, frequently changes in morphology are due to obstruction, main alterations are hydronephrosis and changes in the cortex-medulla relationship. There are four main types of perinephric fluid collections: hematoma, urinoma, abscess, and lymphocel. Imaging features at may overlap; however, differentiation can often be achieved with use of color Doppler US (CDUS), CT and renal scintigraphy in conjunction with ancillary clinical information. Thrombosis of transplanted renal vein: may occur immediately CDUS shows “reverse” diastolic flow and no flow in the renal vein. Stenosis of transplanted renal vein: may be the result of external compression or fibrosis, is seen as 3–4-fold increase in the PSV between the stenotic and prestenotic segments. Stenosis of arterial transplanted renal artery: CDUS shows mosaic pattern at the anastomosis and an increase in peak systolic velocity, the spectral analysis shows “tardus-parvus” waveform. Arteriovenous fistulas and pseudoaneurysm are mainly biopsy complications, fistulas appear as focal areas with color mosaic pattern, spectral analysis may show increased systodiastolic flow in the area of interest with resistive and pulsatility indexes that are often normal or lower and pulsatile acceleration is present, pseudoaneurysms appear as small cystlike anechoic areas containing finely hyperechoic material representing internal thrombi, CDUS reveals turbulence and ‘‘to-and-fro’’ flow. Rejection: renography shows decreased perfusion, diminished uptake and delayed excretion, US demonstrates enlargement and a complete loss of corticomedullary differentiation with end-diastolic flow absent and spectral waveform with reverse flow. Acute tubular necrosis: renal scintigraphy curve demonstrates delayed time to peak activity, US shows a collecting system thickening and effacement of sinus echo complex, spectral waveform has a brisk systolic upstroke and low end-diastolic flow.

Conclusion
CDUS is the primary tool for routine surveillance and initial diagnostic imaging for allograft dysfunction. Improvements in surveillance imaging decreased incidence of graft failure and death within first 5 years after transplant.