Diuretic MAG3 scintigraphy (F₀) in acute pyelonephritis: Regional parenchymal dysfunction and comparison with DMSA

^99mTc-DMSA late static planar imaging or SPECT is being used for the investigation of focal acute pyelonephritis (APN), especially in children with urinary tract infection (UTI). Diuretic ^99mTc-mercaptoacetyltriglycine (MAG3) dynamic scintirenography has been applied in the evaluation of kidney function and structure, frequently to exclude obstruction. However, in children and adults with a clinical picture of APN, diuretic MAG3 scintigraphy with zero time injection of furosemide (MAG3-F₀) was observed to display focal parenchymal abnormalities; regional dysfunction (focal parenchymal decrease in early uptake; slow filling in and prolonged late retention of activity); or, less frequently, fixed defects. This observation was further studied both retrospectively and prospectively, and its sensitivity and specificity for APN were compared with those of dimercaptosuccinic acid (DMSA). Methods: In the retrospective study, for 36 children with UTI and regional parenchymal findings on MAG3-F₀, data were reviewed, analyzed, and compared with the results of concurrent DMSA studies. In the prospective study, for 57 children with clinical and laboratory findings suggestive of APN, the 2 radiopharmaceuticals were used for imaging sequentially and the results of the 2 studies were compared. The criteria for abnormal findings compatible with the diagnosis of APN were, for MAG3-F₀, regional parenchymal dysfunction and fixed focal defects and, for DMSA, focal defects without parenchymal loss. Results: In all groups of patients, most abnormal MAG3-F₀ studies (80%) showed regional parenchymal dysfunction, but in some (20%) a fixed defect was found. Compared with DMSA and when both regional dysfunction and focal defects were considered, MAG3-F₀ was as sensitive as DMSA. Some patients had only MAG3-F₀ abnormalities, suggesting a slightly lower specificity for MAG3-F₀ compared with DMSA (86%); this finding needs further study, because it also raises questions about the sensitivity of DMSA, considering that only a small percentage of patients with clinically suggestive findings had abnormal study findings. In most patients with fixed defects on both DMSA and MAG3-F₀, follow-up studies showed no resolution, suggesting that a fixed defect on MAG3-F₀ may indicate either more severe APN or preexistent scars and that regional dysfunction may be a sign more specific for APN and prognostic of potential recovery. In addition, a pattern more specific for a scar - A fixed defect with a dilated regional calyx - Was seen on follow-up MAG3-F₀. Conclusion: A fast (25-min) planar dynamic MAG3-F₀ study was found to be as sensitive at depicting focal parenchymal abnormalities in APN as was the 3- to 4-h DMSA routine procedure. The sensitivity and specificity of both studies need further evaluation.