MRI and DW-MRI of Acute Pyelonephritis (APN)

An accurate evaluation of acute pyelonephritis (APN) requires imaging of parenchymal involvement. When no predisposing conditions to complicated APN are found at US, noncomplicated APN is suspected, and CT or MRI should be performed. As patients with noncomplicated APN are mostly young women, gadolinium-enhanced (GE) MRI is preferred. Diffusion-weighted (DW) MRI might be quicker and cheaper than standard GE-MRI and is reliable for diagnosing or ruling out noncomplicated APN, due to the high diagnostic agreement with GE-MRI. However, GE-MRI is still mandatory for accurately staging APN within 48 h after diagnosis. DWI with ADC evaluation might be also useful in following therapeutic management of APN, without using ionizing radiation or contrast media.