Aim: To assess the role of Ultrasound (US), US Color Doppler (CD) and Power Doppler (PD) in the diagnosis and in the follow-up of renal graft pathology by evaluating morphological and functional features of the vasculature and comparing these to other clinical parameters.
Material and methods: From January 1990 to June 2000, four hundred and thirty-six renal allograft recipients (mean age 45 years) underwent periodical US, CD and PD (mean follow-up 48 months) to evaluate morphology and perfusion of the graft. Resistive index (RI) and pulsatility index (PI) were measured in order to monitor flow variations from the renal to the arcuate arteries. PD was used mainly to study the morphology of the cortical vessels. The examinations were performed on an Esaote Biomedica AU-4/5 (Genoa, Italy) using a convex 3.5 MHz probe and a linear 7.5 MHz probe. On the basis of clinical data the patients were divided into 3 groups: A) Normal, B) Acute graft dysfunction, C) Chronic allograft nephropathy. In 87 patients (20%) percutaneous biopsy or FNAB was performed. RI and PI mean values +/-SD were calculated and compared to the other diagnostic parameters considered: serum creatinine level, US morphology, CD and PD vascularization. Finally RI and PI for each group were compared using the t -test in order to determine the statistical significance of the correlation between these indices and the patients clinical conditions.
Results: The 436 patients were divided as follows: Group A) 170 patients (39%); Group B) 105 patients (24%); Group C) 161 patients (37%). Urological and surgical complications were ruled out in all patients. RI and PI showed a similar trend exceeding cut-off values in Group B) and C) with highest peaks in Group B. Statistical analysis demonstrated the efficacy of this method in the differentiation between normal and pathological grafts, but there was a reduced statistical difference between the two pathological groups. Histological analysis performed on 87 patients (20%) showed good correlation with RI.
Discussion and conclusions: CD is a non-invasive diagnostic method which provides flow-metric quantitative parameters for the hemodynamic assessment of the renal transplant. These values present a certain sensitivity but are not specific of renal graft dysfunction, as there is no reliable differentiation between acute rejection and other parenchymal pathologies. During the follow-up, RI and PI have no predictive value. RI variations from renal artery to cortical vessels (hylum-cortical ratio) show a good correlation with the clinical evolution of the transplant. The evaluation of RI and PI can generally be limited to renal and interlobar arteries as arcuate sampling is necessary only when the hylum-cortical ratio shows reduction or inversion. Integration of clinical and instrumental diagnoses can reduce the number of biopsies.