Colour-coded duplex sonography in the diagnostic assessment of vascular complications after kidney transplantation in children

Depiction of transplant renal vascular anatomy and complications: unenhanced MR angiography by using spatial labeling with multiple inversion pulses

PURPOSE

To evaluate the ability to depict anatomy and complications of renal vascular transplant with unenhanced magnetic resonance (MR) angiography with spatial labeling with multiple inversion pulses (SLEEK) and to compare the results with color Doppler (CD) ultrasonography (US), digital subtraction angiography (DSA), and intraoperative findings.

MATERIALS AND METHODS

This study was approved by the institutional review board, and written informed consent was received before examination. Seventy-five patients who underwent renal transplantation were examined with unenhanced MR angiography with SLEEK and CD US. DSA was performed in 15 patients. Surgery was performed in eight patients. The ability of SLEEK to show transplant renal vascular anatomy and complications was evaluated by two experienced radiologists who compared the results with CD US, DSA, and intraoperative findings.

RESULTS

Patients successfully underwent SLEEK MR angiography. Transplant renal vascular anatomy was assessed in 87 arteries and 78 veins. Renal vascular complications from transplantation were diagnosed in 23 patients, which included 14 with arterial stenosis, three with arterial kinking, two with arteriovenous fistulas, two with venous stenosis, one with pseudoaneurysms, and one with fibromuscular dysplasia. Three patients had two renal transplants and nine patients had nine accessory renal arteries. More accessory renal arteries were detected with SLEEK than with CD US. Correlation was excellent between the stenosis degree with SLEEK and DSA (r = 0.96; P < .05). For those with significant artery stenosis (>50% narrowing) proved with DSA (n = 7) or surgery (n = 3), positive predictive value was 91% (10 of 11).

CONCLUSION

Unenhanced MR angiography with SLEEK preliminarily proved to be a reliable diagnostic method for depiction of anatomy and complications of renal vascular transplant. It may be used for evaluation of patients with renal transplant, and in particular for those with renal insufficiency.

Interventional therapy of vascular complications following renal transplantation

Renal transplantation is accepted as the preferred treatment for most cases of end-stage renal disease. Postoperative vascular complications include stenosis or thrombosis of the transplant renal artery or arteriovenous fistulas after biopsy. Impaired arterial perfusion of the transplant may be the leading cause for graft dysfunction or refractory hypertension. Therefore, non-invasive imaging modalities are required to detect and locate vascular complications with high accuracy. Doppler ultrasound is suited as a screening method for the detection of impaired graft perfusion. Magnetic resonance imaging (MRI) is used for an accurate diagnosis of vascular complications and to support decision for appropriate surgical or interventional treatment. Minimal invasive techniques like percutaneous transluminal angioplasty and stent placement have evolved as safe procedures with a high technical success rate reducing substantial morbidity. They can be considered as an alternative to surgical treatment of transplant renal artery stenosis (TRAS). Embolization of severe arteriovenous fistulas is the method of choice if the feeding artery can be occluded through a microcatheter. In selected cases, even catheter-guided fibrinolytic treatment of arterial thrombosis might be considered, if instantaneous surgery is considered a high-risk procedure. This article reviews the imaging features of common vascular complications after renal transplantation with focus on MRI. In addition, interventional radiological techniques are described for the treatment of TRAS, acute thrombotic occlusion, and arteriovenous fistulas.

Evaluation of severe transplant renal artery stenosis with Doppler sonography

PURPOSE

To evaluate and determine Doppler criteria for predicting a severe transplant renal artery stenosis (80%-99% diameter reduction) and to compare the Doppler findings in patients with end-to-end and end-to-side anastomosis.

METHODS

We performed Doppler sonography on 16 consecutive patients with transplant renal artery stenosis (TRAS) confirmed by digital subtraction arteriography (DSA). Fourteen patients had end-to-end anastomosis, and 2 had end-to-side anastomosis. Eleven patients were re-evaluated with color Doppler sonography within 4 days after intervention. Seven Doppler parameters, including the peak systolic velocity (PSV) in the renal, iliac and interlobar artery, Pre-PSV ratio (the ratio of the PSV in the renal artery to that in the iliac artery), Post-PSV ratio (the ratio of the PSV in the renal artery to that in the interlobar arteries, acceleration time and resistance index, were measured. In the patients with severe TRAS the measurements of these parameters were compared before and after successful intervention.

RESULTS

In the 16 patients with a single transplanted kidney, arteriography demonstrated 14 main renal arteries with severe stenosis, and 3 renal arteries with moderate stenosis. When using the cutoff values of Post-PSV ratio >13, renal artery PSV >4 m/sec, acceleration time >0.06 second, and resistance index <0.5 for the detection of all 14 severe stenoses, the sensitivities were 100%, 71%, 93%, and 50%, respectively. For assessing all 14 severe stenoses and 12 severe stenoses of end-to-end anastomosis, the cutoff value of Pre-PSV ratio >5 had sensitivities of 86% and 100%, respectively. Pre-PSV ratios in severe stenoses of end-to-end anastomosis (range, 5.1-11.5) were significantly greater than those recorded in severe stenoses of end-to-side anastomosis (range, 2.8-3.1). Statistically significant differences before and after successful intervention were found for all 7 Doppler parameters in the 7 patients with severe stenosis.

CONCLUSIONS

An 80%-99% diameter reduction of the renal artery can be diagnosed based on a Post-PSV ratio >13 for patients with either end-to-end or end-to-side anastomosis. A Pre-PSV ratio >5 for patients with end-to-end anastomosis and acceleration time >0.06 second are helpful in the diagnosis of severe TRAS.

Renal biopsy in high-risk patients with medical diseases of the kidney

The number of high-risk patients undergoing renal biopsy is likely to increase in the near future because of the increased use of anticoagulants for such conditions as atrial fibrillation, combined liver and kidney disease caused by hepatitis C, and the aging of the population. Nephrologists need to become increasingly familiar with evaluating such patients through both specialized management of percutaneous kidney biopsy and alternate methods of renal biopsy, which primarily consist of open (surgical) biopsy, transjugular (transvenous) biopsy, and laparoscopic biopsy. The indications, complications, and general approach to such patients are discussed. This is a US government work. There are no restrictions on its use.