Gadolinium-enhanced three-dimensional magnetic resonance angiography versus conventional digital subtraction angiography: which modality is superior in evaluating living kidney donors?1

3.0Tesla magnetic resonance angiography (MRA) for comprehensive renal evaluation of living renal donors: pilot study with computerized tomography angiography (CTA) comparison

PURPOSE

Most living related donor (LRD) kidneys are harvested laparoscopically. Renal vascular anatomy helps determine donor suitability for laparoscopic nephrectomy. Computed tomography angiography (CTA) is the current gold standard for preoperative imaging; magnetic resonance angiography (MRA) offers advantages including lack of ionizing radiation and lower incidence of contrast reactions. We evaluated 3.0T MRA for assessing renal anatomy of LRDs.

MATERIALS AND METHODS

Thirty consecutive LRDs underwent CTA followed by 3.0T MRA. Data points included number and branching of vessels, incidental findings, and urothelial opacification. Studies were individually evaluated by three readers blinded to patient data. Studies were reevaluated in consensus with discrepancies revealed, and final consensus results were labeled "truth".

RESULTS

Compared with consensus "truth", both computed tomography (CT) and magnetic resonance imaging were highly accurate for assessment of arterial and venous anatomy, although CT was superior for detection of late venous confluence as well as detection of renal stones. Both modalities were comparable in opacification of lower ureters and bladder; MRA underperformed CTA for opacification of upper urinary tracts.

CONCLUSIONS

3.0T MRA enabled excellent detection of comprehensive renal anatomy compared to CTA in LRDs.

Urologic considerations and complications in kidney transplant recipients

Urologic considerations during the kidney transplantation process, starting with initial recipient evaluation and continuing through the post-transplant, long-term follow-up, are critical for minimizing urologic complications and improving graft survival. Appropriate, targeted, preoperative urologic evaluation of the recipient allows for an optimized urinary tract to accept the graft, whereas post-transplant urologic follow-up and monitoring decrease the risk of graft lost secondary to a urologic cause, particularly in patients with a urologic reason for their kidney failure and in those patients with concomitant urologic diagnoses. Urologic complications comprise the second most common adverse post-transplant event, occurring in 2.5% to 14% of patients and are associated with high morbidity, graft loss, and mortality. Early and late urologic complications, including hematuria, hematoma, lymphocele, urine leak, ureteral stricture, nephrolithiasis, and vesicoureteral reflux, and their causes and treatment options are explored. A multidisciplinary team approach to kidney transplantation, including transplant surgery, urology, and nephrology, optimizes outcomes and graft survival. Although the current role of the urologist in kidney transplantation varies greatly by institution, appropriate consultation, participation, and monitoring in select patients is essential.

Urological involvement in renal transplantation

Historically, urologists were the primary surgeons in renal transplantation. Specialization and increased complexity of the field of transplantation, coupled with a de-emphasis of vascular surgical training in urology, has created a situation where many renal transplants are carried out by surgeons with a general surgery background. Because of its genitourinary nature, however, urological input in renal transplantation is still vital. For living donors, a urologist should be involved to help evaluate and prepare certain patients for eventual donation. This could involve both medical and surgical intervention. Additionally, urologists who carry out living donor nephrectomy maintain a sense of ownership in the renal transplant process and provide a unique opportunity to the trainees of that particular program. For renal transplant recipients, preoperative evaluation of voiding dysfunction and other genitourinary anomalies might be necessary before the transplant. Also, occasional surgical intervention to prepare a patient for renal transplant might be necessary, such as in a patient with a small renal mass that is detected by a screening pretransplant ultrasound. Intraoperatively, for patients with complex urological reconstructions that might be related to the etiology of the renal failure (urinary diversion, bladder augmentation), a urologist who is familiar with the anatomy should be available. Postoperatively, urological evaluation and intervention might be necessary for patients who had a pre-existing urological condition or who might have developed something de novo after the transplant. Although renal transplant programs could consult an on-call urologist for particular issues on an as-needed basis, having a urologist, who has repeated exposure to the particular issues and procedures that are involved with renal transplantation, and who is part of a dedicated multidisciplinary renal transplant team, provides optimal quality of care to these complex patients.

Assessment of live kidney donors by magnetic resonance angiography: reliability and impact on outcomes

BACKGROUND

Kidney allograft retrieval from live donors requires accurate determination of kidney anatomy prior to surgery, particularly the arterial supply. Traditionally, conventional angiography has been used to obtain this information. Magnetic resonance angiography (MRA) offers a non-invasive, cost-effective alternative, but has been considered to be less accurate. Despite this criticism, many centers have moved to MRA screening of potential kidney donors. The objective of this study is to evaluate our experience of the reliability of MRA in determining the arterial anatomy of living kidney donors as compared to the intra-operative findings.

METHODS

We performed a retrospective review of gadolinium-enhanced, ultra-fast, three-dimensional, spoiled gradient-echo MRA in live kidney donors in the Southern Alberta Transplant Program and compared these results with the intra-operative findings during nephrectomy, as the gold standard.

RESULTS

Of the 66 patients, an accessory renal artery was found intra-operatively in eight cases; two of which were erroneously diagnosed as normal by MRA. The negative predictive value for MRA was 0.97, false-negative rate was 0.25, and sensitivity was 0.75. No patient experienced side-effects from the MRA procedure. No donor needed conversion to open nephrectomy because of an undetected accessory renal artery. One allograft with an accessory renal artery developed thrombosis of the lower pole of the kidney despite arterial reconstruction. Kidney function in the recipient of this allograft was excellent and there was no urinary leak.

CONCLUSION

In our hands, MRA determined the vascular anatomy of potential kidney donors with an acceptable negative predictive value of 97%.

Laparoscopic Live Donor Nephrectomy: Single Center Experience

AIMS

The aim of this study was a retrospective assessment of the safety of laparoscopic live donor nephrectomy (LLDN) and the outcome of these renal transplantations.

METHODS

From November 2001 to October 2006, we performed 30 LLDN (all left nephrectomies) after excluding any renal vascular anomalies in the donor. All laparoscopic procedures were performed by a team consisting of an expert laparoscopic surgeon and a transplant surgeon. The donor mean age was 48.9 +/- 7.6 years (range 22 to 69), 33% of the donors were men and their mean Body Mass Index was 24.7 +/- 3.8 kg/m(2). The recipients were a 32 +/- 14 years old (range 6 to 64), with 66% of them men, and their mean time on dialysis, 33 +/- 49 months (range 0 to 120).

RESULTS

After a mean follow-up of 39 +/- 14 months, all donors and recipients are alive. The mean operative time was 272 +/- 41 min (range 225-360) and the mean warm ischemia time, 161 +/- 35 seconds (range 107 to 240). Surgical complications in the donors were one incisional hernia and two cases of pneumonia. The donor's mean hospital stay was 5.3 +/- 1.7 days (range 3 to 12) and their mean serum creatinine at discharge was 111 +/- 21 micromol/L. There was one surgical complication-a hematoma-among the recipients, and all transplants functioned immediately except for one case.

CONCLUSIONS

LLDN was confirmed to be safe and effective, with no negative impact on transplants success. Expertise in laparoscopic surgery is needed to minimize the side effects for the transplant donor and for the recipient.

Can magnetic resonance angiogram be a reliable alternative for donor evaluation for laparoscopic nephrectomy?

BACKGROUND

While hand-assisted laparoscopic donor nephrectomy (HLDN) is less invasive, which can encourage kidney donation, it requires more exact information about the renal vascular anatomy because of its limited visual field during nephrectomy. MRA is also an attractive choice because of its minimal invasiveness; further, it is an outpatient-based procedure, it uses non-nephrotoxic contrast material and it has no radiation. The aim of our study was to evaluate the effectiveness of gadolinium enhanced three-dimensional MRA (GdE-3D MRA) in a group of potential live donors who were candidates for HLDN.

METHODS

From September 2002 to December 2004, 40 potential live renal donors were evaluated prospectively with GdE-3D MRA, and this imaging modality was performed before the gold standard, the intra-arterial digital subtraction angiogram (IA-DSA), was carried out. All the images were reviewed in a blinded manner by the attending vascular radiologist. The MRA findings were compared with the DSA findings and the surgical findings as the reference methods. We evaluated the accuracy of MRA for imaging the renal architectures, and especially for imaging the renal accessory arteries and the early branching arteries that are important determinants for selection of the donor kidney.

RESULTS

Both the MRA and DSA images showed consistent findings with the surgical findings in 92.5% of the 40 donors. There were no discrepant cases in depicting the main renal artery. MRA showed 100% specificity for imaging both the renal accessory arteries and the early branching arteries, when compared with the surgical findings. The kappa values for the MRA and DSA for the accessory arteries were all 0.66 compared with the intraoperative findings. MRA also depicted one huge renal cyst in one donor and many small renal cysts in the other donors that could not be imaged by DSA. There were no adverse events during the MRA procedure. None of the findings missed by MRA resulted in deleterious consequences at laparoscopic nephrectomy for the donor and graft.

CONCLUSIONS

Our limited experience with GdE-3D MRA for imaging the renal structures in kidney donor evaluation for HLDN has been quite satisfactory.

Magnetic resonance angiography of chest and abdomen at 3 T

During the past decade, contrast-enhanced magnetic resonance angiography (CE-MRA) has been proven to be a powerful tool to visualize the thoracoabdominal vasculature and, consequently, has become a widely accepted noninvasive imaging modality. With the more recent introduction of high-field whole-body magnetic resonance scanners, a further improvement of diagnostic accuracy can be expected. General considerations for performing high-resolution CE-MRA at higher field strength include the benefits of higher signal-to-noise ratio and an improved contrast between vascular and background tissues. Although there are many positive attributes for performing CE-MRA at 3 T, there are also some tradeoffs, such as static magnetic field inhomogeneity and increase in specific absorption rate. This review describes the main technical innovations of advanced CE-MRA techniques at 3 T, illustrated by characteristic cases.

High-resolution magnetic resonance angiography of the renal arteries using parallel imaging acquisition techniques at 3.0 T: initial experience

OBJECTIVE

The purpose of this prospective study was to investigate the feasibility of high-resolution magnetic resonance angiography (MRA) of the kidneys at 3.0 T using parallel data acquisition.

MATERIAL AND METHODS

Contrast-enhanced MRA of the renal arteries (RA) was performed in 12 volunteers and 12 consecutive patients (mean age 47.1 +/- 16.3 years) on a 3.0 T MR scanner. For CEMRA, a high-resolution 3-dimensional GRE FLASH sequence was implemented. Images were assessed subjectively on a 0 to 5 scoring scale by 2 reviewers. Quantitative evaluation was done by measuring the contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR).

RESULTS

Diagnostic image quality was acquired in all individuals. In total, 62 RA were found, consisting of 48 main and 14 accessory RA. Overall visibility score for main RA was 4.82 +/- 0.38. RA were identified up to the third-order branches in 88%. In 3 of 12 patients, a hemodynamic relevant stenosis was found and proven by conventional angiogram.

CONCLUSION

CEMRA at 3.0 T is advantageous in terms of better SNR and T1 weighting; therefore, measurement time can be reduced and spatial resolution can be increased without corruption of signal yield. Consequently, high-field MRA may be preferred for the evaluation of renal vascular anatomy in potential kidney donors or for the detection of renal artery stenosis.

Urologische Betreuung von Patienten vor und nach Nierentransplantation

Patients with end-stage renal disease awaiting kidney transplantation require regular urological evaluation. The urologist's main task is early diagnosis and treatment of genitourinary malignancies and evaluation of the lower urinary tract. Furthermore, urologists are often confronted with the question of whether or not to perform pretransplant urological surgery, i.e., native nephrectomy for polycystic kidney disease. Urological care after kidney transplantation involves diagnosis and treatment of ureteral complications, malignancies, lower urinary tract symptoms, and last but not least erectile dysfunction, which has a prevalence of 20-50% among kidney transplant recipients. For the evaluation and follow-up of the living kidney donor, international guidelines have been developed in recent years to also help the urologist to perform a correct evaluation and follow-up of the kidney donor.

Evaluation of MR-angiography for pre-operative assessment of living kidney donors

INTRODUCTION

Pre-operative magnetic resonance tomography (MR) and MR-angiography (MRA) have rendered favorable results for the assessment of renal anatomy preceding living-related kidney transplantation. However, limited value of MRA in the detection of accessory renal vasculature is reported.

METHODS

We compared the results of pre-operative contrast-medium-enhanced MRA of the last 30 consecutively performed nephrectomies in living kidney donors with the intraoperative findings of vascular, parenchymal, and ureteral anatomy.

RESULTS

Pre-operative MRA diagnosed a solitary renal artery in 24 cases (80%) and a normal venous, ureteral and parenchymal anatomy in all cases. Intraoperatively, the surgeon confirmed the normal pre-operative MRA findings of ureter and parenchyma. Yet, in 6 out of 30 patients (20%) vascular architecture differed from the pre-operative imaging: four of them, who had a radiologically regular anatomy, were found to have accessory vessels upon surgical preparation. In the fifth patient, MRA revealed an accessory lower polar artery, which was confirmed during surgery. An undiagnosed third arterial vessel, located behind the renal vein, led to an aortic bleeding. In the sixth case, the adrenal gland artery was misinterpreted as an accessory superior polar artery of the kidney in MRA. Additionally, a radiologically undetected inferior polar artery was dissected during nephrectomy and led to partial hypoperfusion of the graft. Subsequent retrospective reevaluation of the MRA by experienced radiologists was unable to identify the intraoperative anatomical discrepancies. Hence, sensitivity of MRA was 60% (6 out of 10 cases) for accessory renal vessel detection and 80% (24 out of 30 cases) for overall sensitivity in determining renal vessel number.

DISCUSSION

MRA is a reliable method for the non-invasive investigation of living kidney donors and provides valuable information required by the surgeon. But, as the technique misses small diameter vessels, it cannot be recommended as sole diagnostic tool in unclear cases.

Pre-donation assessment of kidneys by magnetic resonance angiography and venography: accuracy and impact on outcomes

Reports on the accuracy of magnetic resonance angiography (MRA) and magnetic resonance venography (MRV) in evaluating living donor renovasculature employ few patients or omit the consequences of inaccurate scans. We retrospectively compared intraoperative findings to MRA/MRV scans in 146 donor-recipient pairs. For detecting accessory arteries and early branching, MRA sensitivity was 57.6%, specificity 96.5%, false positive rate 3.5%, false negative rate 42.4%, positive predictive value 82.6%, negative predictive value 88.6% and overall accuracy 87.7%. By excluding clinically inconsequential accessory arteries, MRA sensitivity rose to 73.1%, specificity to 96.7% and overall accuracy to 92.5%. For MRVs, sensitivity was 56.2%, specificity 99%, false positive rate 1%, false negative rate 43.8%, positive predictive value 90%, negative predictive value 94.8% and accuracy 94.5%. Inaccurate scans were associated with prolonged donor and recipient operations and more frequently reconstructed arteries, but did not affect clinical outcomes. Because most missed accessory arteries are inconsequential, MRA is a useful, less invasive method for defining donor renovascular anatomy.

Renal MR angiography

The high accuracy of renal MR angiography makes it well suited for diagnosing renal vascular disease. A comprehensive examination includes three-dimensional gadolinium MR angiography to assess lumenal anatomy and functional techniques to assess the hemodynamic significance of any stenosis identified. Postprocessing is critical to provide reformations, maximum intensity projections, and optional volume-rendered images to display arteries in an angiographic format for optimal demonstration of any vascular lesions. It is important to review source images to avoid missing pathologic findings. As MR imaging continues to develop, the renal MR angiography examination will likely expand to include extensive functional information about creatinine clearance, flow, and response to pharmacologic agents as well as spectroscopy, diffusion, perfusion, phase contrast, and other techniques.