Ultrasonographic evaluation of renal size in dogs with acute allograft rejection

The purpose of this study was to determine the best method to ultrasonographically monitor renal size changes associated with acute allograft rejection in dogs. Qualitative changes in renal cortical and medullary echogenicity were also evaluated, although this was not a major focus of the study. Four unrelated, mixed-breed dogs underwent bilateral nephrectomies and heterotopic renal allograft transplantation. Ultrasound examinations of transplanted kidneys were initiated at 3 days after surgery and continued at 2-3 day intervals until death (38 +/- 2 days). Ultrasound measurements of kidney length, width, height, cross-sectional area, and estimated volume were used to assess relative changes in renal size associated with transplantation and rejection. Transplanted kidneys had a rapid increase in volume and cross-sectional area that averaged 103% and 83% above baseline levels, respectively, by 17 days after transplantation. The increased size was attributed to a combination of hypertrophy and acute rejection, the latter of which was confirmed at postmortem. Kidney volume decreased to approximately 35% above baseline volume by day 34 as rejection became more advanced. Qualitative changes associated with rejection included medullary enlargement with decreased echogenicity early in the study, followed by increased cortical thickness and echogenicity with poor cortical medullary definition in the latter stages of the survival period. It was concluded that relative changes in renal allograft size can be easily monitored with ultrasound. In regard to linear measurements, changes in renal width were more pronounced than changes in height or length with acute rejection. Therefore measurements that incorporate the width, namely volume or cross-sectional area, appear to be the most sensitive for monitoring changes in allograft size. Renal cross-sectional area measurements are preferred because they are simple to perform using the automated calculation capability of most newer ultrasound units.