Ultrasound Parameters and Histopathology Findings in Transplanted Kidney

Abstract

Background: The ability of renal allograft ultrasound to predict histopathology findings of renal biopsy has been a subject of many studies. Some found that different morphological and haemodynamic parameters could predict acute allograft rejection, while other studies found no correlation between renal ultrasound and histopathology findings. Aim: To analyse if parenchymal thickness corrected for renal size, resistance index and some other routinely measured ultrasound parameters can predict histopathology findings on renal biopsy. Patients and methods: We retrospectively analysed 72 renal biopsies and respective allograft ultrasounds which were performed on 68 patients (57 % men) with average age 50 (21 - 73) years, with kidney graft dysfunction in the Nephrology Department of the University Medical Centre Ljubljana in the years 2010 and 2011. An average of 3,8 (0 - 14) days passed between graft biopsy and renal ultrasound. Ultrasound parameters - parenchymal thickness (mm) x 10/ graft size assessed by kidney length (cm) ratio and resistance index were compared with different histopathology diagnoses: acute rejection, chronic rejection, chronic kidney changes, acute tubular necrosis (ATN). Results: Biopsy revealed acute rejection in 47 %, chronic rejection in 22 %, ATN in 18 %, reflux nephropathy in 3 % and a glomerulonephritis in 14%. Chronic changes were described in 64 % of all the biopsies. The mean value of the resistance index and of the parenchymal thickness/ graft size ratio was 0,81 ± 0,10 and 1,48 ± 0,27, respectively. Enlarged parenchymal thickness/graft size ratio was significantly higher in ATN (mean 1,72 ± 0,26) compared with no ATN (mean 1,39 ± 0,23) - p< 0.001, and lower when chronic changes were present (mean 1,4 ± 0,25 for chronic changes vs. mean 1,62 ± 0,28 for no chronic changes), p=0,004. In the group without ATN the index was enlarged in acute graft rejection compared with no graft rejection (mean 1,5 ± 0,24 vs. 1,24 ± 0,13, respectively) - p< 0,001, while in the whole group, that also included ATN, the index showed no differentiating power for acute rejection, p=0,332. Resistance index was significantly higher in ATN than without it (mean 0,91 ± 0,10 vs. 0,79 ±0,08, respectively), p< 0,001, while the index was not increased (but was actually lower) in acute graft rejection compared to no graft rejection, neither in the whole group (mean 0,81 ± 0,09 vs. 0,82 ± 0,12, respectively), p=0,572, nor in the group without ATN (mean 0,80 ± 0,07 vs. 0,82 ± 0,10, respectively), p=0,545. Conclusions: Enlarged parenchymal thickness/graft size ratio on ultrasound was observed in acute tubular necrosis and acute allograft rejection. Resistance index was higher in acute tubular necrosis compared to acute allograft rejection. Decreased parenchymal thickness/ graft size ratio was observed in chronic kidney changes.