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Introduction: Kidney transplant biopsies play a pivotal role in the diagnosis of allograft dysfunction, usually being preceded by renal ultrasound examination. Unlike native kidneys, cortical echogenicity in kidney grafts cannot be directly compared to liver or spleen echogenicity, so that echogenicity assessment relies mostly on corticomedullary differentiation, often in association with Doppler resistivity index calculation.
Methods: This study examined correlations between renal ultrasound/Doppler parameters and histological changes in 194 kidney biopsies. Histological changes were assessed semiquantitatively, based on activity and chronicity indexes derived from lupus nephritis scoring, while ultrasound parameters were analyzed quantitatively through computer-assisted assessment of kidney cortical and medullary pyramid echogenicity in specific areas.
Results: For all biopsies, corticomedullary differentiation showed no correlation with histological changes. However, the medullary pyramid area correlated with the activity score of lesions (r = -0.179; p = 0.028), acute tubular necrosis (r = 0.239; p = 0.021), intimal fibroelastosis (r = -0.186; p = 0.023), and the index of interstitial changes (r = -0.236; p = 0.023). Doppler resistivity index correlated with interstitial fibrosis (r = -0.168; p = 0.039). In initial biopsies (including time-zero biopsies), corticomedullary differentiation correlated with the index of interstitial changes (r = -0.373; p = 0.010), the medullary pyramid area correlated with the activity score of lesions (r = -0.226; p = 0.047), while no correlation was observed between Doppler renal resistivity index and biopsy findings. In later biopsies, corticomedullary differentiation displayed no correlation with histological changes, similar to the overall group. However, the relationship between the medullary pyramid area and intimal fibroelastosis persisted (r = -0.287; p = 0.015). In this subgroup, Doppler resistivity index correlated with the chronicity index (r = -0.269; p = 0.019) and intimal fibroelastosis (r = -0.312; p = 0.006).
Conclusion: The correlation between ultrasound/Doppler parameters and histological changes in kidney transplantation appears weak initially but improves over time, possibly due to the accumulation of histological alterations in the interstitium of transplanted organ.