Changes in renal resistive index after urologic interventions: Were untreated kidneys really affected?

Abstract

I read the article by Dr. Abd Ellah and associates with interest [ [1] Abd Ellah M. Kremser C. Pallwein L. et al. Changes of renal blood flow after ESWL: assessment by ASL MR imaging, contrast enhanced MR imaging, and renal resistive index. European Journal of Radiology. 2010; 76: 124-128 Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar ]. They evaluated 13 patients with renal stone disease with MR imaging and Doppler ultrasound 12 h before and 12 h after SWL. They excluded cases with hydronephrosis and acute renal colic. The mean intra-arterial resistive index (RI) and the difference of mean resistive index (delta RI) were measured from interlobar arteries as we did in our study published recently [ [2] Tokgoz O. Tokgoz H. Unal I. Voyvoda N. Serifoğlu I. Changes in renal Doppler ultrasonographic parameters in patients managed with rigid ureteroscopy. Acta Radiologica. 2013; 54: 327-332 Crossref PubMed Scopus (7) Google Scholar ]. Delta RI was regarded as the mean difference between the post-SWL and pre-SWL RI values in the same kidney. They observed a significant increase in RI in both treated and untreated kidneys. ASL MR imaging findings supported this data, however, no significant changes in the kidneys were noticed on contrast enhanced dynamic MR imaging. Accordingly, we were interested in the changes in renal Doppler ultrasonographic parameters in patients managed with rigid ureteroscopy – instead of SWL – [ [2] Tokgoz O. Tokgoz H. Unal I. Voyvoda N. Serifoğlu I. Changes in renal Doppler ultrasonographic parameters in patients managed with rigid ureteroscopy. Acta Radiologica. 2013; 54: 327-332 Crossref PubMed Scopus (7) Google Scholar ]. In urology practice, during an ureteroscopic operation, because of the irrigation fluid used, the irrigation pressures generated within the collecting system can be elevated, and can cause pyelovenous and pyelolymphatic backflow. This backflow may create a pressure on intrarenal vasculature and may also contribute to the increase in renal vascular resistance. Amount of the irrigation pressures transmitted to the renal pelvis, collecting ducts and subsequently to the parenchyma determine the degree of the vasoconstrictive response that would eventually lead to an increase in RI values. As we hypothesized, RI and delta RI values of the operated kidneys were found to be significantly higher than the values for non-operated kidneys. Delta RI was regarded as the mean difference between the postoperative and preoperative RI values in the same kidney. Related to delta RI in the study by Dr. Abd Ellah, actually, we wondered if delta RI values were significantly different among treated and untreated kidneys. According to data given in Table 1, it seems that no statistically significant difference in delta RI would be detected. Nevertheless, statistical analysis is necessary. The authors explain this simultaneous increase of RI in untreated kidneys by the reduction of blood volume due to spasm of parenchymal vessels, which occurred as a result of the release of vasoactive substances like renin and endothelin. We reached similar data when postoperative (0.60) and preoperative mean RI (0.59) were compared in non-operated (untreated) kidneys. Although the p value was significant (0.014), delta RI was only 0.01 when compared with the operated kidneys (0.05). However, it was not the case for pulsatility index (PI) values. No significant changes in mean PI of the non-operated kidneys were noticed.