Wishing won't make it so: duplex Doppler sonography in the evaluation of renal transplant dysfunction

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.

Polyetiology of Renal Allograft Dysfunction

In 101 consecutive patients with renal allograft dysfunction a correlation of Duplex Doppler sonography (DDS) with histopathologic reports of simultaneously performed biopsies was made. Renal vascular impedance was estimated by calculating the resistive index (RI). A total of 290 different specific histologic diagnoses (mean 2.1 ± 0.84 diagnoses/biopsy) was noted. With increasing time interval to transplantation, single diagnoses as cause of allograft dysfunction decreased. DDS could not reliably differentiate, exclude, or grade any of the common causes of renal allograft dysfunction like vascular and/or cellular rejection, chronic rejection, acute tubular necrosis, cyclosporin nephrotoxicity, relapse of glomerulonephritis and infection. Follow-up studies after established histologic diagnosis in 19 patients with persisting allograft dysfunction demonstrated a lack of sensitivity of DDS to significant superimposed causes of transplant malfunction. We conclude that biopsy is still necessary to direct proper therapy of renal allograft dysfunction.

Ultrasound contrast agents: a promising future

The emerging field of contrast ultrasound has great and untapped potential. Improved vascular enhancement may increase the number and type of diagnostic vascular examinations. Improved vessel depiction may increase examination speed and improve patient throughput. New gray-scale contrast imaging techniques may substantially increase the sonographic detection and characterization of liver, kidney, and other focal parenchymal masses. Contrast ultrasound examinations may increase diagnostic confidence, decrease nondiagnostic studies, and decrease the requirement for additional imaging studies. Further investigation is needed, however, to determine the diagnostic use and cost-effectiveness of this new approach relative to CT, MR imaging, angiography, and conventional ultrasound imaging.

Radionuclide evaluation of renal transplants

Chronic renal failure caused by hypertension or by parenchymal kidney disease is a very common global health problem. Patients with chronic renal failure have two therapeutic options, dialysis and transplantation, of which transplantation has become a preferred modality. This review article is an update of a more comprehensive previous review (Semin Nucl Med, 181-198, 1988) and concentrates on the changes that have taken place in this field in recent years. These changes comprise new criteria for the selection of transplant candidates, newer techniques for the diagnosis of medical and surgical complications after transplantation, the use of new tracers (Tc-99m MAG3), and new antirejection regimens.

Renal transplant sonography: correlation of Doppler and biopsy results in cellular rejection

Seventy-one patients with allograft dysfunction had concomitant Doppler sonography and percutaneous biopsy. Forty-one had biopsy proven acute cellular rejection and eight had acute cellular rejection in combination with acute tubular necrosis. Real time ultrasonic appearance and various parameters of Doppler waveform were studied and compared with 30 controls who had a long period of stable function with no previous episodes of rejection or acute tubular necrosis (ATN). Morphological appearances were unhelpful in diagnosing rejection. A resistive index greater than 0.8 in the study group was highly specific for dysfunction but could not differentiate between acute rejection and ATN. However, two patients in the control group of normal transplants had a resistive index of 0.83. An early to mid diastolic notch was highly specific for acute rejection but of low sensitivity. It may be the only Doppler indication of cellular rejection and may be present when the resistive index is in the normal range.

Follow-up study of renal transplants by duplex Doppler and gray-scale ultrasound

In the early postoperative period after renal transplantation 388 follow-up ultrasound examinations were performed in 77 patients. Over a period of 18 months standardized duplex indices (resistive index, pulsatility index) and gray-scale parameters (parenchyma/sinus index; medulla/cortex index) were sampled. These data were correlated retrospectively with clinical and pathological diagnoses. To delineate the individual course of duplex and gray-scale indices during different transplant diseases we created a new parameter: the MID (maximal index difference) which is a result of the difference between the highest index during the phase of renal dysfunction and the lowest index during the phase of normal renal function. This MID, calculated for duplex indices and for the parenchyma/sinus index, indicated significant differences in the behavior of renal transplants during the four main diseases: interstitial rejection, vascular rejection, acute tubular necrosis and Cyclosporine A nephrotoxicity. Using the MIDs, a table of cut-off values was established, which enables to differentiate retrospectively these four transplant complications with a sensitivity of 84% and specificity of 81%. In our opinion consequent follow-up examinations with duplex and gray-scale sonography should be performed, enabling sonography to become a helpful diagnostic instrument in the monitoring of renal transplants.

Duplex Doppler ultrasound in the investigation of occult nephropathy following haemolytic uraemic syndrome

Duplex doppler ultrasound has been reported to be of value in the detection of raised vascular resistance, particularly in the renal tract. A prospective single blind study investigating the use of duplex Doppler ultrasound to measure resistive index (RI) in patients with impaired renal function and a history of diarrhoea-associated haemolytic uraemic syndrome (D+ HUS) was performed. There was considerable overlap in the range of RIs, with RIs greater than 70% in children with normal renal function and in those with renal impairment following D+ HUS. There was no significant difference in the mean RI between the groups studied. We feel that the RI is not of value in predicting the presence of occult nephropathy following haemolytic uraemic syndrome.

Clinical value of Doppler ultrasound in the first two months after kidney transplant

The ability of PI measurements to differentiate between acute rejection and ATN was investigated in 37 patients, who were frequently examined by duplex Doppler after kidney transplant. Absolute PI values as well as increase in PI were recorded and the clinical course was correlated with these pulsatility measurements. PI values were evaluated in 70% of patients undergoing acute rejection. However, in the majority of patients with ATN, the PI was evaluated from the start and continued to rise to an average of 8 days post-transplant. This rise in PI in patients with ATN suggests that pulsatility measurements are unreliable tests to differentiate acute rejection from ATN in the early post-transplant period.