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Background
Infectious and inflammatory renal pathologies are often diagnosed with clinical and laboratory information; however, diagnostic imaging is valuable in patients with atypical infection, complications of infection, and those not responding to medical management. Computerized tomography (CT) is the gold standard for imaging renal infection or inflammation due to its high sensitivity and accuracy in detecting calcification or gas, in identifying renal parenchymal perfusion changes, and in characterizing space occupying lesions in the kidney or perinephric space (including inflammatory masses, abscesses, and retroperitoneal collections). Ultrasound (US) and magnetic resonance imaging (MRI) can also be useful, particularly in instances of iodine allergy, renal insufficiency, or pregnancy when CT cannot be utilized. We will present a multimodality pictorial review of infectious and inflammatory renal conditions and complications.

Educational Goals / Teaching Points
Through this exhibit, the viewer will be able to identify and characterize various common and uncommon renal infectious and inflammatory conditions via a multimodality case-based pictorial review. We will illustrate acute, chronic, and atypical renal infectious and inflammatory conditions, explore potential complications, and draw attention to imaging diagnoses that require emergent treatment or intervention. Additionally, we aim to highlight the strengths and weaknesses of modalities such as US, CT, MRI, and positron emission tomography (PET) in characterizing these renal conditions.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The presentation will highlight key signs, features and recommended management of renal infectious and inflammatory conditions, including but not limited to acute/chronic pyelonephritis, emphysematous pyelonephritis/pyelitis, pyonephrosis, fungal infection and aspergillosis, renal tuberculosis and putty kidney, xanthogranulomatous pyelonephritis, inflammatory pseudotumor, renal replacement lipomatosis, granulomatosis polyangiitis, IgG4 related renal disease, and renal sarcoidosis. We will also review infectious complications such as renal and perinephric abscess and diagnoses requiring percutaneous drainage or nephrostomy. CT is the gold standard for diagnostic imaging of renal conditions in addition to clinical and laboratory analysis. In certain situations when CT or iodinated contrast cannot be used, there is utility in using US and/or MRI for diagnostic workup and understanding these infectious and emergent renal imaging features is important!

Conclusion
Cross sectional imaging serves as a key problem-solving tool in multiple clinical scenarios. While CT is most commonly utilized as the gold standard, occasionally US or MR is performed first or in lieu of CT. Thus, it is especially essential to recognize a variety of renal infectious and inflammatory conditions and their multimodality imaging appearance to avoid misdiagnosis as well as guide timely and appropriate management. This presentation aims to review and increase the reader's familiarity with such infectious and inflammatory renal conditions and complications.