Imaging Manifestations of Acute and Chronic Renal Infection That Mimics Malignancy: How to Make the Diagnosis Using Computed Tomography and Magnetic Resonance Imaging

To review the computed tomography and magnetic resonance imaging manifestations of acute and chronic renal infections that may mimic malignancy and to provide useful tips to establish an imaging diagnosis. Acute and chronic bacterial pyelonephritis are usually readily diagnosed clinically and on imaging when the diagnosis is suspected based upon clinical presentation. When unsuspected, focal, extensive or mass-like, acute and chronic bacterial pyelonephritis may mimic infiltrative tumours such as urothelial cell carcinoma (UCC), lymphoma, and metastatic disease. Infection may be suspected when patients are young and otherwise healthy when there is marked associated perinephric changes and in the absence of metastatic adenopathy or disease elsewhere in the abdomen and pelvis. Renal abscesses, from bacterial or atypical microbial agents, can appear as complex cystic renal masses mimicking cystic renal cell carcinoma. Associated inflammatory changes in and around the kidney and local invasion favour infection. Emphysematous pyelonephritis can mimic necrotic or fistulizing tumour; however, infection is more likely and should always be considered first. Xanthogranulomatous pyelonephritis can mimic malignancy when focal or multifocal and in cases without associated renal calculi. Malacoplakia is an inflammatory process that may mimic malignancy and should be considered in patients with chronic infection. Bacillus Calmette-Guerin (BCG)-induced pyelonephritis is rare but can mimic renal malignancy and should be considered in patients presenting with a renal mass when being treated with BCG for urinary bladder UCC. Examiner les signes visibles par tomodensitométrie et imagerie par résonance magnétique des infections rénales aiguës et chroniques pouvant se confondre avec les tumeurs malignes et obtenir des outils efficaces permettant d’établir un diagnostic par imagerie. La pyélonéphrite aiguë et chronique d'origine bactérienne est habituellement facilement diagnostiquée de manière clinique, ou par recours à l'imagerie en cas de soupçon sur la base du tableau clinique. Lorsqu'elle n'est pas soupçonnée, la pyélonéphrite bactérienne focale aiguë et chronique, extensive ou semblable à des masses, peut ressembler à des tumeurs infiltrantes (les carcinomes urothéliaux, les lymphomes et les maladies métastatiques, par exemple). On peut soupçonner une infection chez les patients de jeune âge, par ailleurs en bonne santé, en présence de modifications périrénales importantes