Detection of obstructive uropathy and assessment of differential renal function using two functional magnetic resonance urography tools

Summary

Aim: After detection of obstructive uropathy (OU), the indication for or against surgery is primarily based on the differential renal function (DRF). This is to compare functional magnetic resonance urography (fMRU) with dynamic renal scintigraphy (DRS) to assess OU and DRF in infants and children. Patients, methods: Retrospective analysis in 30 patients (female: 16; male: 14; median age: 5.5 years [0.2-16.5]), divided into subgroup A (age: 0-2 years; n = 16) and B (> 2-17 years; n = 14). fMRU was assessed by measuring renal transit time (RTT) and volumetric DRF with CHOP fMRU tool (CT) and ImageJ MRU plug-in (IJ). OU detection by fMRU was compared with DRS (standard of reference) using areas under the curves (AUC) in ROC analyses. Concordant DRF was assumed if absolute deviation between fMRU and DRS was < 5 %. Results: DRS confirmed fixed OU in 4/31 kidneys (12.9 %) in subgroup A. AUC of CT was 0.94 compared with 0.93 by IJ. Subgroup B showed fixed OU in 1/21 kidneys (4.8 %) with AUCs of 0.98 each. RTT measured neither by CT nor by IJ in confirmed fixed OU was < 1200 s – resulting in negative predictive values of 1.0 each. In subgroup A, DRF was concordant in 81.3 % of the kidneys for CT and DRS compared with 75.0 % for IJ and DRS. In subgroup B, CT and DRS were concordant in 91.7 %, and IJ and DRS in 45.8 % of the kidneys. Conclusion: fMRU accurately excluded fixed OU in infants and children, independent from the software used for quantification. However, assessment of DRF with fMRU deviated from DRS especially in infants who may profit most from early intervention. Thus, fMRU cannot fully replace DRS as primary functional examination. If, for clinical reasons, fMRU is performed in first place and it cannot exclude fixed OU, it should be followed by DRS for validation and DRF quantification.

Zusammenfassung

Ziel: Nach der Detektion einer obstruktiven Uropathie (OU) basiert die Indikation für oder gegen eine chirurgische Intervention v. a. auf der seitengetrennten Nierenfunktion (DRF). In der Studie wurde die funktionelle Magnetresonanzurographie (fMRU) mit der Nierensequenzszintigraphie (DRS) in der Beurteilung von OU und DRF verglichen. Methoden: Retrospektive Studie mit 30 Kindern (weiblich: 16; männlich: 14, medianes Alter:5,5 Jahre [0,2-16,5]) unterteilt in Gruppe A (Alter: 0-2 Jahre; n = 16) und B (> 2-17 Jahre; n = 14). Die fMRU wurde mittels „renal transit time” (RTT) und „volumetric DRF” im CHOP fMRU Tool (CT) und ImageJ MRU Plug-in (IJ) ausgewertet. Die Korrektheit zur OU-Detektion wurde mit der DRS (Referenzstandard) in ROC-Analysen mittels Area under the curve (AUC) verglichen. Eine konkordante DRF lag bei Abweichung von fMRU und DRS < 5 % vor. Ergebnisse: Die DRS bestätigte eine fixierte OU in 4/31 Nieren (12,9 %) in Gruppe A. Die AUC für CT betrug 0,94, für IJ 0,93. In Gruppe B zeigte sich eine fixierte OU in 1/21 Nieren (4,8 %) mit AUCs von je 0,98 für CT und IJ . Weder für CT noch für IJ lag die RTT < 1200 s bei bestätigter fixierter OU - der negative prädik- tive Wert lag somit bei je 1,0. In Gruppe A maßen CT und DRS die DRF in 81,3 % der Nieren konkordant, IJ und DRS in 75,0 %. In Gruppe B waren CT und DRS in 91,7 % konkordant, IJ und DRS in 45,8 %. Schlussfolgerung: Die fMRU konnte eine fixierte OU bei Säuglingen und Kindern unabhängig von der verwendeten Software zuverlässig ausschließen. Allerdings zeigte die fMRU-DRF Abweichungen von der DRS, besonders im wichtigen Alter bis 2 Jahre. Insgesamt kann die fMRU die DRS nicht vollständig als vorrangige funktionelle Bildgebung ersetzen. Wenn sie doch, aus klinischen Gründen, an erster Stelle erfolgt und eine fixierte OU nicht ausschließen kann, sollte eine DRS zur Validierung und DRF-Bestimmung folgen.

Keywords

obstructive uropathy - fMRU - diuretic renal scintigraphy - CHOP fMRU tool - ImageJ MRU plug-in - renal transit time

Schlüsselwörter

obstruktive Uropathie - fMRU - Nierensequenzszintigraphie - CHOP fMRU Tool - ImageJ MRU Plug-in - renal transit time

^* both authors contributed equally

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