Extrarenal Factors Influencing Resistance Index in Stable Kidney Transplant Recipients

Shear wave elastography and Doppler ultrasound in kidney transplant recipients

Objective

To evaluate the association between shear wave elastography parameters and arterial resistance in kidney transplant recipients.

Materials and Methods

This was a prospective cross-sectional study involving consecutive adult kidney transplant recipients. All patients underwent color Doppler to evaluate the resistive index (RI) and ultrasound shear wave elastography for the quantification of renal allograft stiffness.

Results

We evaluated 55 patients, of whom 9 (16.4%) had an RI defined as abnormal (≥ 0.79) and 46 (83.6%) had an RI defined as normal (< 0.79). The mean age was higher in the abnormal RI group than in the normal RI group (68.0 ± 8.6 years vs. 42.6 ± 14.1 years; p < 0.001), as was the mean shear wave velocity (2.6 ± 0.4 m/s vs. 2.2 ± 0.4 m/s; p = 0.013). Multivariate analysis identified two independent predictors of arterial resistance: age (OR = 1.169; 95% CI: 1.056 to 1.294; p = 0.003) and shear wave velocity (OR = 17.1; 95% CI: 1.137 to 257.83; p = 0.040).

Conclusion

We observed an association between rigidity in the cortex of the transplanted kidney, as evaluated by shear wave elastography, and arterial resistance, as evaluated by color Doppler, in kidney transplant recipients.

Sonography of the renal allograft: Correlation between doppler sonographic resistance index (RI) and histopathology

INTRODUCTION

Allograft rejection (AR), chronic allograft injury (CAI) and acute tubular necrosis (ATN) can lead to renal allograft dysfunction after kidney transplantation. Interstitial fibrosis/tubular atrophy (Banff classification 2005) describes chronic allograft injury with no specific etiology, thus explaining the common final endpoint of various (immunologic and non immunologic) etiologies. The aim of this study was to evaluate correlations between the Doppler sonographic RI-values and histopathological changes of renal allografts biopsies during rejection, acute tubular necrosis and chronic allograft injury as well as the influence of donor and recipient features on the intrarenal RI-values.

METHODS

102 allograft biopsies and ultrasound reports of 69 patients with kidney transplantation performed at the hospital Klinikum rechts der Isar (Technische Universität München, Germany) between 2009 and 2013 were analyzed retrospectively (41 biopsies of living donors, 61 biopsies of deceased donors). Chronic allograft injury was described using the IFTA (interstitial fibrosis and tubular atrophy) or the ECAI score (extended chronic allograft injury score). The ECAI score was built out of the chronic histological lesions glomerulopathy, interstitial fibrosis, tubular atrophy and fibrous intimal thickening (cg + ci + ct + cv) of the BANFF scoring.

RESULTS

Intrarenal RI-values were significantly higher in patients with allograft rejection than without rejection (median 0,79 vs. 0,73; inter quartile range: 0,20 vs. 0,13; p = 0,018). The same was found for T-and non-T cell mediated rejection (median 0,78 vs. 0,73; inter quartile range 0,20 vs. 0,13; p = 0,039). There were no significant differences in the RI-values between the subtypes of T-cell mediated rejection (type IA-IIB). Furthermore, there were no significant differences of RI-values regarding antibody-mediated rejection (present vs. not present) or type of rejection (T-cell- vs. antibody mediated rejection). Patients with rejection and simultaneously chronic allograft injury showed significantly higher RI-values than patients with only chronic allograft injury. Analyses using the IFTA or the ECAI score showed comparable results (IFTA p = 0,043; Score p = 0,021). The intrarenal RI-value was neither able to detect chronic allograft injury nor to distinguish between acute tubular necrosis and rejection. The intrarenal RI-value showed a significant correlation with recipient age (p < 0,001) but not with donor features.

CONCLUSION

In summary, the intrarenal RI-value can indicate a rejection but gives no clear hint to acute tubular necrosis and cannot differentiate from it. Since patients with rejection can have normal RI-values, a biopsy should always be performed in case of suspected rejection. The intrarenal RI-value has no unambiguous validity to determine intrinsic values of the renal allograft, but should rather be understood and interpreted as a systemic parameter influenced by multiple factors.

Renal intraparenchymal resistive index: the ultrasonographic answer to many clinical questions

The use of renal resistive indices (RRIs) for the study of renal microcirculation has in the past been proposed for the identification of renal organ damage or even to specifically identify injury to some areas of the renal parenchyma. Nevertheless, according to the most recent evidences from literature this organ-based conception of RRIs has been proven to be partial and unable to explain the RRIs variations in clinical settings of sepsis or combined organ failure of primitively extrarenal origin or, more generally, the deep connection between RRIs and hemodynamic factors such as compliance and pulsatility of the large vessels. The aim of this review is to explain the physiopathological basis of RRIs determination and the most common interpretative errors in their analysis. Moreover, through a comprehensive vision of these Doppler indices, the traditional and emerging clinical application fields for RRIs are discussed.

Rejection evaluation after renal transplantation using MR diffusion tensor imaging

Background Renal allograft dysfunction monitoring is mainly performed using the serum creatinine (SC) level, Doppler ultrasound (US), or renal biopsy. Recently proposed diffusion-based magnetic resonance imaging (MRI) methods have been explored as new, non-invasive tools for assessing renal function after transplantation. Purpose To investigate the value of fractional anisotropy (FA) measurements in the evaluation of acute rejection cases after renal transplant. Material and Methods Doppler US and MRI diffusion tensor imaging (DTI) were performed in 21 patients with graft dysfunction requiring graft biopsy after renal transplantation and in 21 patients with normal graft function. The MR examinations were performed on a 1.5-T MRI using two b-values (0 and 800 s/mm²). FA values were measured from the cortex and medulla of the transplanted kidney at the upper, middle, and lower poles. Results Twenty-one transplant patients diagnosed with acute rejection (Group 1) were compared to the control group of 21 transplant patients with normal graft function (Group 2). The measured FA values of the medulla were 0.19 ± 0.02 and 0.22 ± 0.05 ( P = 0.017) for Groups 1 and 2, respectively. On the other hand, the measured FA values of the renal cortex were 0.18 ± 0.04 and 0.18 ± 0.04 ( P = 0.97) for Groups 1 and 2, respectively. Conclusion The good correlation between the renal medulla FA values and allograft function shows that MR DTI has potential for non-invasive functional assessment of transplanted kidneys. On the other hand, the renal cortex FA values had no correlation with the allograft function.

Is carotid sonography a useful tool for predicting functional capabilities in ischemic stroke patients following carotid artery stenting?

Carotid stenosis is a major cause of stroke and timely intervention with stenting manipulation can significantly reduce the risk of secondary stroke. The impact of stenting procedures on patient functional capabilities has not yet been explored. The primary aim of this study was to examine associations between periprocedural carotid sonography parameters and post-treatment functional capabilities in stroke patients.Sixty-seven patients who received carotid stenting at 1 angiography laboratory were included. Prestenting and poststenting carotid duplex data were recorded and resistance index (RI) differences at various carotid system locations were compared. The modified Rankin Scale (mRS) was used to assess functional capability. All of the studied parameters were analyzed by SPSS (version 16.0, SPSS Inc, Chicago, IL).Following stenting, mRS scores improved (n = 44) or remained stationary (n = 23). Net contralateral internal carotid artery (ICA) RI for patients with improved mRS was lower compared to that for patients with stationary mRS (median = 0.040 vs 0.11; P = 0.003). The contralateral common carotid artery RI before and after stenting differed significantly (P < 0.050) in both. The ipsilateral ICA RI differed (P < 0.050) only in patients with improved mRS. The difference in mean transit time, Barthel index, net ipsilateral ICA RI, net contralateral external carotid artery RI, postipsilateral common carotid artery RI, and postipsilateral ICA RI differed significantly between different baseline stroke severity groups (P < 0.050).Carotid artery stenting improved physical function in a proportion of ischemic stroke patients with carotid stenosis. Carotid ultrasound is a useful assessment tool to predict likely functional outcomes following carotid artery stenting.

Role of Extracranial Carotid Duplex and Computed Tomography Perfusion Scanning in Evaluating Perfusion Status of Pericarotid Stenting

Carotid stenting is an effective treatment of choice in terms of treating ischemic stroke patients with concomitant carotid stenosis. Though computed tomography perfusion scan has been recognized as a standard tool to monitor/follow up this group of patients, not everyone could endure due to underlying medical illness. In contrast, carotid duplex is a noninvasive assessment tool and could track patient clinical condition in real time. In this study we found that “resistance index” of the carotid ultrasound could detect flow changes before and after the stenting procedure, thus having great capacity to replace the role of computed tomography perfusion exam.

Initial kidney graft resistance index and the long-term cardiovascular mortality in transplanted patients: a paired grafts analysis

BACKGROUND

Cardiovascular complications remain the most frequent cause of death in kidney transplant recipients. We analysed the prognostic value of early measured resistance index (RI) in the aspect of long-term cardiovascular mortality. In order to eliminate potential donor-related confounders, we analysed the mortality of recipients, transplanted with organs procured from the same donor, in whom the initial RI values substantially differed.

METHODS

Doppler sonography was performed in 725 consecutive kidney graft recipients early after transplantation. We identified 133 pairs (266 patients) who received their kidney grafts from the same donor and their initial RI values differed by >0.1.

RESULTS

During 109 ± 37 months of follow-up after transplantation, 84 patients lost their graft and 29 died, 14 of them due to cardiovascular causes. Two groups of paired patients with higher RI and lower RI did not differ significantly with respect to their age, BMI, HLA mismatch and cold ischaemia time. There were more patients with diabetes in the higher RI group (14.3 versus 6.8%). Survival analysis revealed a higher mortality for cardiovascular (8.3 versus 2.3%, P = 0.02) and all causes (14.3 versus 7.5%, P = 0.06) among patients with higher initial RI values. In the Cox regression model, not including age, a higher RI value was a strong predictor of cardiovascular death (HR = 4.88), independent of previous cardiovascular episodes (HR = 6.78). Both these variables lost its significance as a predictors after inclusion of age in the regression model.

CONCLUSION

Increased intrarenal resistance index in the early posttransplant period may help to identify the recipients with increased cardiovascular risk.

Functional MRI detects perfusion impairment in renal allografts with delayed graft function

Delayed graft function (DGF) after kidney transplantation is not uncommon, and it is associated with long-term allograft impairment. Our aim was to compare renal perfusion changes measured with noninvasive functional MRI in patients early after kidney transplantation to renal function and allograft histology in biopsy samples. Forty-six patients underwent MRI 4–11 days after transplantation. Contrast-free MRI renal perfusion images were acquired using an arterial spin labeling technique. Renal function was assessed by estimated glomerular filtration rate (eGFR), and renal biopsies were performed when indicated within 5 days of MRI. Twenty-six of 46 patients had DGF. Of these, nine patients had acute rejection (including borderline), and eight had other changes (e.g., tubular injury or glomerulosclerosis). Renal perfusion was significantly lower in the DGF group compared with the group with good allograft function (231 ± 15 vs. 331 ± 15 ml·min−1·100 g−1, P < 0.001). Living donor allografts exhibited significantly higher perfusion values compared with deceased donor allografts ( P < 0.001). Renal perfusion significantly correlated with eGFR ( r = 0.64, P < 0.001), resistance index ( r = −0.57, P < 0.001), and cold ischemia time ( r = −0.48, P < 0.01). Furthermore, renal perfusion impairment early after transplantation predicted inferior renal outcome and graft loss. In conclusion, noninvasive functional MRI detects renal perfusion impairment early after kidney transplantation in patients with DGF.