Renal transplantation is the most commonly performed solid organ transplant procedure. Monitoring renal transplants with ultrasound is a critical component in the management of transplant patients both in the immediate aftermath of surgery and longitudinally. Many complications are detectable via ultrasound evaluation with relative prevalence dependent on the time since surgery. It is critical for the practicing radiologist to recognize these complications to help guide appropriate treatment. Fundamental understanding of the procedure, including various surgical techniques is of great importance. In this article, the sonographic findings of the most common postoperative and long-term complications of renal transplantation are reviewed. As complications are highly related to surgical technique, the most common surgical techniques are presented first. Comprehensive ultrasound evaluation of the allograft is discussed next, followed by extensive review of the ultrasound findings of common complications. Finally, select recent advances in ultrasound are presented with their current and potential applications to renal transplant evaluation.

Renal transplantation remains the treatment of choice in patients with end-stage renal disease as the 5-year survival rates for the graft in renal transplant patients range from 72% to 99%. Despite improvements in graft survival related to increased efficacy of immunosuppression drugs and improvements in surgical technique, various complications do occur. Ultrasound is the first-line imaging modality for the evaluation of renal transplants in the immediate postoperative period and for longitudinal follow-up. Various other imaging techniques serve as complementary examinations in specific clinical settings. Angiography remains the reference standard for arterial complications and is used for nonsurgical intervention, but noninvasive CT or MR angiography could be considered prior to an invasive procedure. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Ultrasound (US) plays a primary role in the assessment and diagnosis of renal and ureteral pathologies and their management. It is considered the first-line imaging modality for evaluation of urinary obstruction, nephrolithiasis, and urinary retention among other indications. US is also essential for evaluation of renal vasculature and assessment of renal transplantation. Contrast-enhanced US is an advanced application of US gaining its acceptance in evaluation of the renal masses.

Renal transplant is the first-line treatment of end-stage renal disease. The increasing number of transplants performed every year has led to a larger population of transplant patients. Complications may arise during the perioperative and postoperative periods, and imaging plays a key role in this scenario. Contrast-enhanced US (CEUS) is a safe tool that adds additional value to US. Contrast agents are usually administered intravenously, but urinary tract anatomy and complications such as stenosis or leak can be studied using intracavitary administration of contrast agents. Assessment of the graft and iliac vessels with CEUS is particularly helpful in identifying vascular and parenchymal complications, such as arterial or venous thrombosis and stenosis, acute tubular injury, or cortical necrosis, which can lead to graft loss. Furthermore, infectious and malignant graft involvement can be accurately studied with CEUS, which can help in detection of renal abscesses and in the differentiation between benign and malignant disease. CEUS is also useful in interventional procedures, helping to guide percutaneous aspiration of collections with better delimitation of the graft boundaries and to guide renal graft biopsies by avoiding avascular areas. Potential postprocedural vascular complications, such as pseudoaneurysm, arteriovenous fistula, or active bleeding, are identified with CEUS. In addition, newer quantification tools such as CEUS perfusion are promising, but further studies are needed to approve its use for clinical purposes. ©RSNA, 2024 Supplemental material is available for this article.

Page's kidney is a condition that occurs due to external renal compression, usually caused by a subcapsular haematoma, generating a renal compartmental syndrome with parenchymal damage and renal perfusion alteration. Classically associated with renal trauma, Page's kidney can also arise after invasive renal procedures, such as renal biopsies or percutaneous nephrostomies. Clinically, it can trigger hypertension due to activation of the renin-angiotensin system induced by hypoperfusion secondary to renal parenchymal compression and can also present with varying degrees of renal function impairment. Furthermore, severe acute renal failure may be found particularly in patients with solitary kidneys or renal transplants. We present two cases of Page's kidney after renal biopsy and their PoCUS ultrasound findings. We would like to highlight the reversed diastolic flow on Doppler ultrasound in this entity, a pattern we have found in all two cases.

Transplant renal vein thrombosis is a rare complication after kidney transplantation, which can seriously threaten graft survival. Though the measures like thrombolytic therapy or operative intervention could be taken to deal with this complication, allograft loss is the most common outcome. Thus, early finding as well as decisive intervention is crucial to saving the graft. Here we present a 46-year-old male patient who underwent kidney transplantation from a cadaveric donor who developed a transplant renal venous thrombosis induced by acute diarrhea more than 1 year after renal transplantation with an initial symptom of sudden anuria and pain in the graft area. Subsequently, serum creatinine levels increased to 810.0 μmol/L. Pelvic CT showed increased vascular density of the transplanted kidney, and contrast-enhanced ultrasound confirmed venous thrombosis. The patient was treated with heparin sodium alone and diuresis gradually resumed. After more than 1 year of follow-up, serum creatinine returned to the baseline level prior to thrombosis. Our case indicates that quick ancillary examination and treatment without hesitation would be indispensable in rescuing allografts with renal vein thrombus. Unfractionated heparin can be recommended as an effective treatment for mid-long-term renal transplantation patients with renal vein thrombosis.

Kidney grafts are the most common transplanted solid organ. To optimize graft survival, radiologists should be familiar with the anatomy and potential complications unique to transplanted kidneys. In addition to being able to recognize the imaging characteristics to diagnose etiologies of kidney graft dysfunction, an understanding of the pathophysiology is a key to narrowing the differential diagnosis. This article provides a summary of the most common complications based on broad categories of type of complication and posttransplant timing.

Reversal of arterial diastolic flow is commonly considered a sign of transplant renal vein thrombosis until proven otherwise, with the differential including acute rejection, acute tubular necrosis, and perirenal hematoma. We discuss a case of a patient who presented with decreased urine output on the second postoperative day following living unrelated kidney transplantation. Doppler ultrasound was performed and demonstrated reversal of diastolic flow in the transplant renal artery. Prompt surgical exploration revealed intraluminal blood clot obstructing the ureter. To our knowledge, this is the first reported case of reversed diastolic flow secondary to ureteral obstruction by an intraluminal blood clot.

Kidney transplantation (KT) is an effective treatment for end-stage renal disease. Despite their rate has reduced over time, post-transplant complications still represent a major clinical problem because of the associated risk of graft failure and loss. Thus, post-KT complications should be diagnosed and treated promptly. Imaging plays a pivotal role in this setting. Grayscale ultrasound (US) with color Doppler analysis is the first-line imaging modality for assessing complications, although many findings lack specificity. When performed by experienced operators, contrast-enhanced US (CEUS) has been advocated as a safe and fast tool to improve the accuracy of US. Also, when performing CEUS there is potentially no need for further imaging, such as contrast-enhanced computed tomography or magnetic resonance imaging, which are often contraindicated in recipients with impaired renal function. This technique is also portable to patients' bedside, thus having the potential of maximizing the cost-effectiveness of the whole diagnostic process. Finally, the use of blood-pool contrast agents allows translating information on graft microvasculature into time-intensity curves, and in turn quantitative perfusion indexes. Quantitative analysis is under evaluation as a tool to diagnose rejection or other causes of graft dysfunction. In this paper, we review and illustrate the indications to CEUS in the post-KT setting, as well as the main CEUS findings that can help establishing the diagnosis and planning the most adequate treatment.

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 high-risk 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 contrast-enhanced 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, US-guided 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.^©RSNA, 2019.

Vascular complications are a significant source of morbidity and mortality among renal transplant recipients. Imaging using ultrasound, CT, and MRI plays a key role in diagnosing such complications. This review focuses on the major vascular complications of renal grafts, which include transplant renal arterial and venous stenoses, arterial and venous thromboses, arteriovenous fistulas, and pseudoaneurysms. Etiology, diagnostic modalities useful for diagnosis, and imaging appearance will be presented.

Renal transplantation is the treatment of choice in patients with end-stage renal disease because the 5-year survival rates range from 72% to 99%. Although graft survival has improved secondary to the introduction of newer immunosuppression drugs and the advancements in surgical technique, various complications still occur. Ultrasound is the first-line imaging modality for the evaluation of renal transplants in the immediate postoperative period and for long-term follow-up. In addition to depicting many of the potential complications of renal transplantation, ultrasound can also guide therapeutic interventions. Nuclear medicine studies, CT, and MRI are often helpful as complementary examinations for specific indications. Angiography remains the reference standard for vascular complications and is utilized to guide nonsurgical intervention. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer-reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Torsion is an uncommon cause of impaired function in a renal transplant. We present a case of intraperitoneal transplant torsion secondary to adhesions to the left fallopian tube and ovary. Inability to confirm renal venous flow with Doppler misled to the erroneous sonographic diagnosis of renal vein thrombosis, although end diastolic flow was absent rather than reversed. The correct diagnosis was made with CT. The combination of abnormal orientation of the graft on ultrasonography, acutely impaired renal function, and abnormal Doppler study should have led to a diagnosis of transplant torsion. The case is also unusual in that the lead point was adnexal pathology. © 2017 Wiley Periodicals, Inc. J Clin Ultrasound 45:528-530, 2017.

The purpose of this study was to assess the sensitivity of ultrasound in evaluating peritransplant hematomas that require surgical evacuation in recipients of kidney transplants.

Thirty-four patients who underwent 37 hematoma evacuations underwent ultrasound examinations in the 24 hours before surgical evacuation. The operative reports were evaluated for presence and size of collection, presence of active bleeding at operation, and composition of the hematoma. The clinical findings leading to the ultrasound examination were recorded. Ultrasound examinations were evaluated in consensus by two board-certified and fellowship-trained abdominal radiologists for the presence, size, and echogenicity of the collection; subjective perfusion visualized with color and power Doppler ultrasound; velocities of the renal arteries; and arcuate artery resistive indexes.

Ten of the 37 imaged hematomas (27%) had either no or small (< 50 mL) fluid collections on ultrasound examination. With sonographic volumetry, the reported intraoperative volumes were underestimated by 46%. The mean arcuate artery resistive index was 0.82 in the superior pole, 0.81 in the mid pole, and 0.78 in the inferior pole of the kidney. A decrease in hemoglobin level was the most sensitive clinical finding for determining the presence of perigraft hematomas.

Our results suggest that gray-scale sonography alone appears to have limited sensitivity in detecting clinically significant peritransplant hematomas and that its use may result in overall underestimates of hematomas.

Ultrasonography is an excellent tool for evaluation of the renal transplant in the immediate postoperative period and for long-term follow-up. In this article, normal imaging findings and complications of renal transplantations are described. Disease processes are divided into vascular, perinephric, urologic and collecting system, and parenchymal abnormalities. Attention is paid to the time of occurrence of each complication, classic imaging findings, and potential pitfalls.

Kidney transplantation is the treatment of choice in end-stage renal disease, given the better quality of life of transplanted patients when compared with patients on maintenance dialysis. In spite of surgical improvements and new immunosuppressive regimens, parts of transplanted grafts still develop chronic dysfunction. Ultrasonography, both in B-mode and with Doppler ultrasound, is an important diagnostic tool in case of clinical conditions which might impair kidney function. Even though ultrasonography is considered fundamental in the diagnosis of vascular and surgical complications of the transplanted kidney, its role is not fully understood in case of parenchymal complications of the graft. The specificity of Doppler is low both in case of acute complications, such as acute tubular necrosis, drugs toxicity and acute rejection, and in case of chronic conditions, such as chronic allograft nephropathy. Single determinations of resistance indices present low diagnostic accuracy, which is higher in case of successive measurements performed during the follow-up of the graft. Modern techniques such as tissue pulsatility index, maximal fractional area and contrast-enhanced ultrasound increase ultrasonography diagnostic power in case of parenchymal complications of the transplanted kidney.

We will show the sonographic appearance of peritransplant venous collaterals in renal transplants with renal venous hypertension. Three cases of renal transplants with pericapsular vessels were identified at our institution. Two cases were related to renal vein thrombosis. The third case had pericapsular vessels secondary to venous hypertension from arterialization of the transplant renal vein by a preexisting right thigh arteriovenous graft. The development of high venous pressures in renal transplants leading to the collaterals' venous drainage has been rarely described. This finding should be recognized as a rare complication of renal transplants but does not necessarily lead to transplant failure.

To evaluate renal allograft vessels in the early period after kidney transplantation with three-dimensional (3D) contrast-enhanced MR angiography (3D CE MRA) using a parallel imaging technique.

Sixty-three consecutive patients were examined with 3D CE MRA and integrated SENSE technique (Sensitivity Encoding) 2 to 21 days after renal transplantation. MR angiography studies were analyzed for the presence of arterial stenosis. The degree of renal transplant artery stenosis was graded qualitatively as <50% = mild, 50-70% = moderate, 70-99% = severe, and occlusion. Four patients (6.3%) with moderate (n = 1) or severe (n = 3) arterial stenoses on CE MRA underwent selective intra-arterial digital subtraction angiography. In two patients, selective intravenous digital subtraction angiography (DSA) was performed.

Twenty-seven (42.9%) of the 63 patients had normal CE MR angiograms, 29 (46%) showed mild, 3 patients (4.8%) moderate, and 4 patients (6.3%) severe stenoses of the donor artery. In three patients, the severe stenosis of the graft artery was confirmed by surgery or intra-arterial DSA. One patient with suspicion of severe arterial stenosis on MRA had moderate vessel narrowing on DSA. Twelve months after kidney transplantation, serum creatinine levels were not significantly different in patients with mild and moderate stenoses from those without (P > 0.19) but significantly different from those with severe stenoses (P < 0.05).

The incidence of mild and moderate vessel narrowing at the arterial anastomosis is unexpectedly high in the early period after kidney transplantation and is most likely due to surgery-related tissue edema.