Role of multi-parametric ultrasonography for the assessment and monitoring of functional status of renal allografts with histopathological correlation

Abstract

Background: The study focuses on the use of multi-parametric ultrasound [gray scale, color Doppler and shear wave elastography (SWE)] to differentiate stable renal allografts from acute graft dysfunction and to assess time-dependent changes in parenchymal stiffness, thereby assessing its use as an efficient monitoring tool for ongoing graft dysfunction. To date, biopsy is the gold standard for evaluation of acute graft dysfunction. However, because it is invasive, it carries certain risks and cannot be used for follow-up monitoring. SWE is a non-invasive imaging modality that identifies higher parenchymal stiffness values in cases of acute graft dysfunction compared to stable grafts.

Aim: To assess renal allograft parenchymal stiffness by SWE and to correlate its findings with functional status of the graft kidney.

Methods: This prospective observational study included 71 renal allograft recipients. Multi-parametric ultrasound was performed on all patients, and biopsies were performed in cases of acute graft dysfunction. The study was performed for a period of 2 years at Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, a tertiary care center in north India. Independent samples t-test was used to compare the means between two independent groups. Paired-samples t-test was used to test the change in mean value between baseline and follow-up observations.

Results: Thirty-one patients had experienced acute graft dysfunction at least once, followed by recovery, but none of them had a history of chronic renal allograft injury. Mean baseline parenchymal stiffness in stable grafts and acute graft dysfunction were 30.21 + 2.03 kPa (3.17 + 0.11 m/s) and 31.07 + 2.88 kPa (3.22 + 0.15 m/s), respectively; however, these differences were not statistically significant (P = 0.305 and 0.252, respectively). There was a gradual decrease in SWE values during the first 3 postoperative months, followed by an increase in SWE values up to one-year post-transplantation. Patients with biopsy-confirmed graft dysfunction showed higher SWE values compared to those with a negative biopsy. However, receiver operating characteristic analysis failed to show statistically significant cut-off values to differentiate between the stable graft and acute graft dysfunction.

Conclusion: Acute graft dysfunction displays higher parenchymal stiffness values compared to stable grafts. Therefore, SWE may be useful in monitoring the functional status of allografts to predict any ongoing dysfunction.

Keywords: Acute graft rejection; Multi-parametric ultrasound; Renal allograft; Renal transplant; Resistive index; Shear wave elastography.

Figure 1

Study population inclusion process. BMI: Body mass index.

Figure 2

Graphical representation of linear regression analysis of kPa values of parenchymal stiffness. A: Serum creatinine; B: Estimated glomerular filtration rate (eGFR).

Figure 3

Graphical representation of linear regression analysis of interlobar artery resistive index values. A: Serum creatinine; B: Estimated glomerular filtration rate (eGFR).

Figure 4

Receiver operating characteristic analysis between acute graft dysfunction and stable grafts based on serum creatinine levels. ROC: Receiver operating characteristic.

Figure 5

Quantitative elastography measurement at the interpolar region of a transplant kidney with acute allograft dysfunction due to acute tubular necrosis. A: Gray scale image; B: Color-coded map elasticity values distribution on a scale of 0 to 80 kPa and corresponding gray scale image (mean value 350 kPa and 3.4 m/s); C: Histopathological section shows acute tubular injury with dilation of tubules (blue arrow) and flattening of tubular epithelial cells (orange arrow; × 100 original magnification, H&E stain, scale bar = 100 μm).

Figure 6

Quantitative elastography measurement at the interpolar region of a transplant kidney with acute allograft dysfunction due to acute cellular rejection. A: Gray scale image; B: Color-coded map of elasticity value distribution on a scale of 0 to 80 kPa and corresponding gray scale image (mean value 346 kPa and 3.4 m/s); C: Histopathological section shows severe tubulitis (blue arrow) along with tubulo-interstitial inflammation (black arrow) and interstitial edema (white arrow) in a case of Acute T cell Mediated Cellular Rejection Banff Grade IB (× 100 original magnification, PAS stain, scale bar = 100 μm).

Figure 7

Quantitative elastography measurement at the interpolar region of a transplant kidney with acute allograft dysfunction due to calcineurin inhibitor toxicity. A: Gray scale image; B: Color-coded map of elasticity value distribution on a scale of 0 to 80 kPa and corresponding gray scale image (mean value 331 kPa and 3.3 m/s); C: Histopathological section shows features of CNI toxicity in form of beaded nodular adventitial fibrosis (green arrow) from a case of renal allograft recipient (× 400 original magnification, PAS stain, scale bar = 200 μm).