Diffusion-weighted MRI: new paradigm for the diagnosis of interstitial oedematous pancreatitis
Contrast-enhanced multidetector CT represents the mainstay technique for staging acute pancreatitis (AP). However, MRI on state-of-the art scanners is increasingly used to diagnose acute abdominal disorders thanks to faster, motion-resistant sequences with improved spatial resolution and limited need for patient cooperation. Following an introduction on the role of imaging in AP including the current Atlanta classification, this review focuses on diffusion-weighted imaging (DWI), a functional MRI technique that provides information on water diffusion in the extracellular space, tissue cellularity and capillary perfusion. In recent years, some studies reported that DWI is highly sensitive to pancreatic inflammation, even in mild forms with normal contrast-enhanced CT appearance. Even though apparent diffusion coefficient (ADC) values are heterogeneous among different scanners and sequences, DWI is preferable to CT to avoid administering ionizing radiation and intravenous contrast. In our experience, a rapid non-contrast MRI acquisition protocol including high b value DWI is a valid non-invasive option for early diagnostic confirmation of mild AP, preferable to CT in young people and in patients with impaired renal function or allergy to iodinated contrast medium. Some imaging examples are provided. Since ADC values of mass-forming AP overlap with those of carcinomas, DWI should be interpreted together with clinical and laboratory findings, conventional MRI sequences, MRCP and contrast-enhanced study.