Imaging of Renal Transplant Complications throughout the Life of the Allograft: Comprehensive Multimodality Review

Abstract

The kidney is the most commonly transplanted solid organ. Advances in surgical techniques, immunosuppression regimens, surveillance imaging, and histopathologic diagnosis of rejection have allowed prolonged graft survival times. However, the demand for kidneys continues to outgrow the available supply, and there are efforts to increase use of donor kidneys with moderate-or highrisk profiles. This highlights the importance of evaluating the renal transplant patient in the context of both donor and recipient risk factors. Radiologists play an integral role within the multidisciplinary team in care of the transplant patient at every stage of the transplant process. In the immediate postoperative period, duplex US is the modality of choice for evaluating the renal allograft. It is useful for establishing a baseline examination for comparison at future surveillance imaging. In the setting of allograft dysfunction, advanced imaging techniques including MRI or contrastenhanced US may be useful for providing a more specific diagnosis and excluding nonrejection causes of renal dysfunction. When a pathologic diagnosis is deemed necessary to guide therapy, USguided biopsy is a relatively low-risk, safe procedure. The range of complications of renal transplantation can be organized temporally in relation to the time since surgery and/or according to disease categories, including immunologic (rejection), surgical or iatrogenic, vascular, urinary, infectious, and neoplastic complications. The unique heterotopic location of the renal allograft in the iliac fossa predisposes it to a specific set of complications. As imaging features of infection or malignancy may be nonspecific, awareness of the patient's risk profile and time since transplantation can be used to assign the probability of a certain diagnosis and thus guide more specific diagnostic workup. It is critical to understand variations in vascular anatomy, surgical technique, and independent donor and recipient risk factors to make an accurate diagnosis and initiate appropriate treatment. ©

Contrast‐Enhanced Ultrasound for the Evaluation of Renal Transplants

“…Additionally, the risk of scarring to the renal allograft and resultant impairment of renal function must be considered. Thus, the threshold for imaging should be lower 41 …”

Role for contrast-enhanced ultrasound in assessing complications after kidney transplant

“…Similar to grayscale US, the image quality of CEUS can be impaired by patient-related factors, such as presence of bowel gas, large body habitus, or limited cooperation and physical obstacles in the early postoperative period (wounds or surgical bandage). It should be pointed out that those factors are of less impact on image quality than in other body districts, since the renal graft is usually placed extraperitoneally into the right or left iliac fossa[ 4 ], i.e ., in a superficial and fixed position making the graft easily accessible by US waves.…”

“…Ultrasound (US) with color Doppler analysis has become the preferred imaging tool to evaluate the graft status within the first 24 h after KT[ 3 ]. Together with serial biopsies of the allograft parenchyma, this technique plays also a pivotal role in post-KT surveillance, aiming to diagnose post-surgical complications, acute rejection, or chronic allograft nephropathy[ 3 , 4 ]. On the other hand, color Doppler US is characterized by a low specificity, with Doppler-derived measures, such as the resistance index (RI), not directly reflecting the status of microcirculation[ 5 ].…”

“…In subspecialized centers, this technique is used to assess the graft status after KT due to its portability, safety profile of US contrast agents (UCAs), rapidity of execution, and diagnostic accuracy. Indeed, CEUS allows the evaluation of both macro- and micro-circulation, as well as perirenal collections or parenchymal abnormalities such as those related to rejection, acute tubular necrosis (ATN), impaired perfusion, and focal lesions[ 4 ]. CEUS candidates as the ideal first-line examination to screen for post-KT complications and to refer positive patients to prompt intervention.…”

Role of Mri Corticomedullary Differentiation in the Assessment of Renal Post Transplantation Complications

“…(1) Medical functional complications after renal transplantation include acute rejection(AR), acute tubular necrosis (ATN), cyclosporine toxicity(CsT) and chronic graft rejection(CGR). (2) Various modalities are used for evaluation of the transplanted kidney, ultrasound, Doppler, Radioisotope imaging and MRI. Ultrasound is mainly used for assessment of morphological changes, Doppler for vascular changes, Radioisotope for functional changes, while MRI can be used as one stop imaging technique for assessment of all complications of the transplanted kidney (3).…”