Acute bacterial pyleonephritis on MRI: value of DWI
15 weeks pregnant with 2 weeks of right flank pain and fever. Positive urine culture for E.coli.
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3 wedge-shaped foci of restricted diffusion (b = 800msec) confirmed on the ADC map with subtle heterogeneity on T2 imaging. Note hydronephrosis (mild) greater on the right due pregnancy.
CT should be avoided in pregnancy for pyleonephritis diagnosis thus MRI without gadolinium is a reasonable alternative.
Due to the increased cellularity (inflammatory cells) in the region of infection, there is restricted diffusion of water molecules (extra and intracellular).