Diuretic MAG3 scintigraphy (F-0) in acute pyelonephritis: Regional parenchymal dysfunction and comparison with DMSA

Tc-99m-DMSA late static planar imaging or SPECT is being used for the inves tigation of focal acute pyelonephritis (APN), especially in children with u rinary tract infection (UTI). Diuretic Tc-99m-mercaptoacetyltriglycine (MAG 3) dynamic scintirenography has been applied in the evaluation of kidney fu nction and structure, frequently to exclude obstruction. However, in childr en and adults with a clinical picture of APN, diuretic MAG3 scintigraphy wi th zero time injection of furosemide (MAG3-F-o) was observed to display foc al parenchymal abnormalities; regional dysfunction (focal parenchymal decre ase in early uptake; slow filling in and prolonged late retention of activi ty); or, less frequently, fixed defects. This observation was further studi ed both retrospectively and prospectively, and its sensitivity and specific ity for APN were compared with those of dimercaptosuccinic acid (DMSA). Met hods: In the retrospective study, for 36 children with UTI and regional par enchymal findings on MAG3-F-o, data were reviewed, analyzed, and compared w ith the results of concurrent DMSA studies. In the prospective study, for 5 7 children with clinical and laboratory findings suggestive of APN, the 2 r adiopharmaceuticals were used for imaging sequentially and the results of t he 2 studies were compared. The criteria for abnormal findings compatible w ith the diagnosis of APN were, for MAG3-Fo, regional parenchymal dysfunctio n and fixed focal defects and, for DMSA, focal defects without parenchymal loss. Results: In all groups of patients, most abnormal MAG3-F-o studies (8 0%) showed regional parenchymal dysfunction, but in some (20%) a fixed defe ct was found. Compared with DMSA and when both regional dysfunction and foc al defects were considered, MAG3-F-o was as sensitive as DMSA. Some patient s had only MAG3-F-o abnormalities, suggesting a slightly lower specificity for MAG3-F-o compared with DMSA (86%); this finding needs further study, be cause it also raises questions about the sensitivity of DMSA, considering t hat only a small percentage of patients with clinically suggestive findings had abnormal study findings. In most patients with fixed defects on both D MSA and MAG3-F-o, follow-up studies showed no resolution, suggesting that a fixed defect on MAG3-F-o may indicate either more severe APN or preexisten t scars and that regional dysfunction may be a sign more specific for APN a nd prognostic of potential recovery. In addition, a pattern more specific f or a scar-a fixed defect with a dilated regional calyx-was seen on follow-u p MAG3-F-o. Conclusion: A fast (25-min) planar dynamic MAG3-F-o study was f ound to be as sensitive at depicting focal parenchymal abnormalities in APN as was the 3- to 4-h DMSA routine procedure. The sensitivity and specifici ty of both studies need further evaluation.