Nuclear Medicine in the Evaluation of the Renal Transplant

There is also a related post on the use of ultrasound in evaluation of renal transplants.

Immediate (first week) complications:

• Acute tubular necrosis (ATN): More common in cadaveric transplants. There is preserved or only mildly reduced perfusion with increased T_max and T_1/2. Dynamic imaging reveals marked parenchymal retention. Nice images can be found at RiT Radiology.
• Accelerated acute rejection: Presents within a few days to a few weeks following transplantation.
• Renal vein thrombosis: Decreased or absent perfusion with increased T_max and T_1/2. In complete thrombosis, there is a reniform photopenic area outlined by background activity.
• Renal artery thrombosis: Decreased or absent perfusion with increased T_max and T_1/2. In complete thrombosis, there is a reniform photopenic area outlined by background activity.

Early (1-4 weeks) complications:

• Acute rejection: There is decreased perfusion and increased T_max and T_1/2. These findings may be similar to those of acute tubular necrosis. The time course of disease appearance can help differentiate the two. In addition, acute rejection will show decrease in function on serial radionuclide imaging studies, highlighting the importance of obtaining a baseline study.
• Urine leak or fistula: May see excreted radiotracer adjacent to transplanted kidney.
• Ureteral obstruction: Findings are similar to those of ureteral obstruction in native kidneys.

Late (> 4 weeks) complications:

• Drug toxicity: Acute cyclosporine toxicity resembles mild acute rejection or acute tubular necrosis, with normal or decreased perfusion and with parenchymal retention.
• Renal artery stenosis: Most common vascular complication of transplantation. Findings are similar to those of chronic rejection, with decreased perfusion, normal parenchymal transit, and absent or minimal cortical retention. Post-captopril images will show findings seen in renovascular hypertension: decreased activity with DTPA and increased parenchymal retention with MAG-3.
• Recurrence of native renal disease:
• Lymphocele: Most are asymptomatic and do not require therapy, but some can exert mass effect and impair renal function. A large photopenic region may be seen exerting mass effect on the transplanted kidney.
• Chronic rejection: Thin cortex and mild hydronephrosis with diminished uptake of tracer and normal parenchymal transit. Early chronic rejection may have absent or minimal cortical retention, but there may be parenchymal retention of radiotracer with advanced chronic rejection.

References

• Brown ED, Chen MY, Wolfman NT, Ott DJ, Watson NE Jr. Complications of renal transplantation: evaluation with US and radionuclide imaging. Radiographics. 2000 May-Jun;20(3):607-22.
• Mettler FA and Guiberteau MJ. Chapter 10. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. pp 314-318.