Added value of restricted diffusion in acute pyelonephritis: Two cases with different clinical presentations

Acute pyelonephritis (APN) is characterized as infection of the renal parenchyma and collecting system generally evaluated by integrating clinical assessment, blood tests, urinalysis, and urine culture. If complications are suspected, computed tomography (CT) is the preferred modality; however, if inconclusive or contraindicated, magnetic resonance imaging (MRI) can provide valuable diagnostic information, though less well-described in literature. Herein, we report 2 cases in which MRI demonstrated restricted diffusion in the kidneys, corresponding to APN. In the first case, MRI confirmed findings established by CT (acute lobar nephronia); in the other, MRI provided primary diagnostic evidence of APN after indeterminate CT and US in a patient with prior history of acute pyelonephritis.