Usefulness of the resistive index for the evaluation of transplanted kidneys

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.

High Resistive Index in Transplant Kidneys Is a Possible Predictor for Biopsy Complications

BACKGROUND

Transplant kidney biopsies are performed to determine a histological diagnosis for specific patient treatment. The aim of this study was to investigate if Resistive Index (RI) could be a predictor for biopsy complications.

METHODS

In this study, 220 consecutive transplant kidney biopsies (136 men and 84 women; median age, 55.5 years) were prospectively included. RI (median, 0.7) was measured by use of ultrasound. Histological diagnoses and biopsy complications were registered. Biopsy needles were either 16- or 18-gauge. Biopsies were performed by radiologists and were carried out as an outpatient procedure (70%) or an inpatient procedure (30%). Usually three passes per biopsy were performed.

RESULTS

The overall complication rate was 6.8%, divided into major (4.5%) and minor (2.3%) complications. An RI ≥0.8 predicts major (13.3% versus 3.2%; risk ratio [RR], 4.2; confidence interval [CI], 1.3-14.1; P = .03) and overall biopsy complications (16.7% versus 5.3%; RR, 3.2; CI, 1.2-8.6; P = .04) compared with RI <0.8. In the group <0.8, RI correlated with age (r_s = 0.28, P < .001) and systolic blood pressure (r_s = 0.18, P = .02). In the group ≥0.8, RI correlated with degree of interstitial fibrosis (r_s = 0.65, P = .006) and systolic blood pressure (r_s = 0.40, P = .03). The multiple regression analysis showed that in the group <0.8, the RI correlated only with age (P < .001), whereas in the group ≥0.8, RI correlated only with the degree of interstitial fibrosis (P = .003).

CONCLUSIONS

An RI ≥0.8 indicates greater risk for major and overall biopsy complications and should result in greater caution after biopsy.

The relationship between renal resistive index, arterial stiffness, and atherosclerotic burden: the link between macrocirculation and microcirculation

The renal resistive index (RRI) measured by Doppler sonography is a marker of microvascular status that can be generalized to the whole of the arterial tree. Its association with large-vessel dysfunction, such as arterial stiffness or the atherosclerotic burden, can help to establish physiopathological associations between macrocirculation and microcirculation. The authors conducted a cross-sectional study of hypertensive patients (n=202) and a healthy control group (n=16). Stiffness parameters, atherosclerotic burden, and determination of the RRI in both kidneys were performed. The average RRI was 0.69±0.08 and was significantly greater in patients with diabetes and chronic kidney disease. Renal resistive index positively correlated with age, creatinine, and albuminuria. Positive correlations were found with arterial stiffness parameters (pulse wave velocity, ambulatory arterial stiffness index, and 24-hour pulse pressure), as well as atherosclerotic burden and endothelial dysfunction measured as asymmetric dimethylarginine in serum. In the multivariate analysis, independent factors for increased RRI were age, renal function, 24-hour diastolic blood pressure, and arterial stiffness. The authors concluded that there is an independent association between renal hemodynamics and arterial stiffness. This, together with the atherosclerotic burden and endothelial dysfunction, suggests that there is a physiopathologic relationship between macrovascular and microvascular impairment.

Complications of renal transplantation: ultrasonographic evaluation

OBJECTIVE

The purpose of this presentation is to show the ultrasonographic findings of complications of renal transplantation.

METHODS

We reviewed the ultrasonographic findings of complications of renal transplantation, including urologic complications, fluid collections, graft dysfunction, vascular complications, neoplasms, and recurrent native renal disease.

RESULTS

Specific ultrasonographic features of complications of renal transplantation have been illustrated.

CONCLUSIONS

Familiarity with the clinical setting and the appearance of potential renal transplant complications as depicted with the most commonly used modality, ultrasonography, will facilitate prompt, accurate diagnosis and treatment.

Color Doppler Findings in Transplanted Kidneys and Remnant Kidneys of Donors 6 to 12 Months After Kidney Transplantation

OBJECTIVES

Ultrasonography and color Doppler have been used extensively in the evaluation of transplanted kidney. The aim of this study was evaluation and comparison of color Doppler sonography findings in the remnant kidney of living donors and the transplanted kidney at 6 to 12 months after kidney transplantation.

METHODS

In a cross-sectional study we evaluated ultrasonographic (US) and color Doppler findings in 20 kidney allograft recipient and donors. Group 1 were unrelated and related kidney donors, and group 2, allograft recipients. Color Doppler US was performed by one sonologist on the remnant kidney of the living donor and the transplanted kidney of the recipient at 6 to 12 months after kidney donation and transplantation. We recorded, kidney size (including length and anteroposterior diameter), cortical thickness, resistive index (RI), and pulsatile index (PI). Statistical analysis was performed using SPSS 13 win (t test) for comparison of the results in donors and recipients. All data are presented as mean values +/- SD with P values less than .05 considered significant.

RESULTS

In group 1, mean age of kidney allograft recipients was 39.92 +/- 11.95 years with male-to-female ratio of 1/2. Mean length, width, and cortical thickness of the transplanted kidney were 120.15 +/- 11.95 mL, 53.65 +/- 7.50 mL, and 8.53 +/- 1.00 mL, respectively. Mean RI and PI were 0.60 +/- 0.08 and 1.02 +/- 0.23, respectively. Mean serum creatinine was 1.23 +/- 0.24 mg/dL. Mean duration of renal transplantation was 7.27 +/- 1.10 months. In group 2, mean age of recipients was 25.63 +/- 3.50 years with male-to-female ratio of 1/10. Mean length, anteroposterior diameter, and cortical thickness were 120.77 +/- 9.28 mL, 53.36 +/- 4.52 mL, and 9.04 +/- 1.27 mL, respectively. Mean RI and PI were 0.60 +/- 0.02 and 1.07 +/- 0.13, respectively. There was no significant difference in the length, anteroposterior diameter, cortical thickness, RI, and PI of donors and transplanted kidneys at 6 to 12 months after transplantation (P>.05). There was a significant increase in both donor and recipient kidney size at 6 to 12 months after transplantation (P<.05).

CONCLUSION

It seems that renal US and Doppler parameters remain stable in the recipient and donor at least upon short-term evaluation. Long-term study with more patients is recommended.