Comparison of MAG-3-DMSA scintigraphic methods in determining differential renal function in ureteropelvic junction obstruction

Ureteropelvic junction obstruction (UPJO) is the most common cause of clinically significant antenatal hydronephrosis. Since it may cause permanent kidney damage in the future, it is crucial to manage UPJO correctly and decide on surgical treatment at the appropriate time. Conditions such as symptomatic status, degree of hydronephrosis, and loss of function in the kidney are guiding factors in the follow-up of patients. However, there is no clear guideline for the patients' follow-up or surgical treatment decision (time and indications). Ultrasonography (USG) is the best imaging method for the diagnosis, follow-up, and treatment decision of UPJO. In addition to USG, mercaptoacetyltriglycine (MAG-3) and dimercaptosuccinic acid (DMSA) scintigraphies, which are nuclear medicine imaging methods, are used in the follow-up of patients. Differential renal function can be calculated with scintigraphic methods, unlike radiological imaging methods. Differential renal function is the distribution of total kidney function by both kidneys. However, studies suggest that MAG-3 scintigraphy overestimates the differential renal function (supranormal function) in UPJO and that DMSA scintigraphy shows the differential renal function more accurately. Our study aimed to compare MAG-3 and DMSA scintigraphic methods in determining differential renal function in UPJO. It aimed to question whether follow-up with MAG-3 scintigraphy was sufficient in the follow-up of patients with UPJO and to determine kidney function and the necessity of DMSA scintigraphy. The patients who were followed up with the diagnosis of UPJO in our clinic in the last ten years and who had both MAG-3 and DMSA scintigraphy were analyzed retrospectively, the differential functions were reexamined from the system, and the results of the scintigraphy, USG findings, and treatment approaches (non-surgical management, pyeloplasty) were compared. When differential renal function were compared in DMSA and MAG-3 results, a statistically significant positive and strong correlation was found in the kidney with UPJO (p=0.0001, r=0.752). When the MAG-3 and DMSA results were classified in the kidney with UPJO (supranormal, normal, low function) in the determination of differential renal functions, there was a consistency of 76%, and it was correlated. The kappa coefficent was p=0.0001/k=0.456. While two patients had a supranormal function and 13 patients had a low function in MAG-3, five patients had a supranormal function, and eight patients had a low function in DMSA. The rate of supranormal function in DMSA was higher than that in MAG-3. MAG-3 detected low-functioning kidneys more frequently than DMSA. Contrary to the literature, we found that the supranormal measurement rate of MAG-3 scintigraphy was low. In addition, the reason for measuring supranormal function in terms of differential renal function and the relationship between the analyzed data in terms of affecting factors (kidney size, parenchymal thinning, renal pelvis anterior- posterior diameter) and supranormal function were evaluated. While increased kidney size was significantly associated with supranormal function in DMSA, no effect of other parameters on supranormal function was found in DMSA and MAG-3 scintigraphy. However, this may be related to the small number of patients measured supranormal. The results of our study suggested that there is no need to use both scintigraphic methods in each UPJO, that follow-up with MAG-3 may be sufficient, in patients with cortical defect suspicion or surgery decision DMSA may be taken before the operation in order to determine the basal cortical function. Keywords; Ureteropelvic junction obstruction, differential renal function, Supranormal function, MAG-3, DMSA