The importance of renal Doppler ultrasonographic evaluation in acute ureteral obstruction in pregnant women

Abstract

I read the article by Dr. Pepe and associate with interest [1]. They evaluated 234 pregnant women asymptomatic in 204 cases and with unilateral renal colic in 30 by duplex Doppler and conventional Ultrasonography to detect possible renal/ureteral pathology. The mean intra-arterial resistive index (RI) and the difference of mean resistive index between both kidneys (delta RI) were measured from interlobar arteries as we did in our study published recently [2]. A renal RI [ 0.70 and/or a 10 % difference between the kidneys were considered as diagnostic of obstructive uropathy. The detected mean RI for obstructed kidneys was significantly higher than a mean RI of contralateral normal kidneys. Accordingly, we were interested in the changes in renal Doppler ultrasonographic parameters in patients managed with rigid ureteroscopy [2]. In urology practice, during a 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 greater 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. In contrast, in the study by Pepe et al., the difference in mean RI of the obstructed and contralateral kidneys was accepted as delta RI. In anyway, both studies reveal the importance of RI measurements in obstructed cases. In current clinical practice, Doppler ultrasonographic measurements and relevant RI values are not regarded as the primary diagnostic modalities in the functional evaluation of the urinary tract. If we accept ureteroscopic investigation somehow a simulation of a ureteral obstruction, in all suspected ureteral/ renal obstructions (whatever the cause is), evaluation via Doppler ultrasonography may guide the clinician to determine the obstructive degree of renal units. With the calculation of delta RI, increase in RI values in renal units when compared to contralateral ones should be determined, thereby the amount of obstructive stress/pressure on diseased kidney might be suspected. In clinical perspective, by this way, the clinician can have an idea of the obstructive degree of a certain pathology. Hence, treatment options would more readily and correctly be decided. For example, a ureteral stone in a pregnant woman might be treated with conservative medical expulsive therapy if delta RI is low, or it may be eliminated by endoscopic surgery within a short period of time if delta RI is high. Difficulty in determining a certain threshold value for delta RI remains a problematic issue, since delta RI values range just between 0.00 and 0.10 as in our study. Percent calculations, as Dr. Pepe preferred (10 % RI difference between kidneys), can rather be more suggestive and discriminative. In conclusion, we advice delta RI measurements in acute renal colic to determine the degree of obstructive stress on O. Tokgoz (&) Department of Radiology, School of Medicine, Bulent Ecevit University, Hastanesi S-Blok Kat:4, Kozlu, Zonguldak 67600, Turkey e-mail: h_tokgoz@hotmail.com