It has been more than 30 years since the Bosniak classification of cystic renal masses was first proposed (1). This CT-based classification was introduced in 1986 and originally divided cystic renal masses into one of four classes after exclusion of infectious, inflammatory, and vascular etiologies (Table 1) (1). Since then, refinements have reduced the number of benign masses in Bosniak class III (2-9). For example, Bosniak IIF (where the F is for follow-up) was added for cystic masses with many thin (or minimally thickened) septa with "perceived" enhancement, large (.3 cm) homogeneous nonenhancing hyperattenuating masses, and masses with thick or non-border-forming calcification.Bosniak summarized these changes in 2012 and contended that Bosniak I and II masses were "clearly benign," Bosniak IV masses were "clearly malignant," Bosniak IIF masses were "probably benign," and Bosniak III masses were "indeterminate" (approximately half were malignant and half were not) (9). These adaptations enabled radiologists and urologists to render specific management recommendations: Bosniak I and II masses have been ignored, Bosniak IIF masses have been followed, and Bosniak III and IV masses historically have been treated unless substantial comorbidities or limited life expectancy would warrant observation instead (10-12).

CT texture analysis can be used to accurately differentiate fp-AML from RCC on unenhanced CT images.

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Purpose of review:Use of gadolinium-based contrast agents (GBCA) in renal impairment is controversial, with physician and patient apprehension in acute kidney injury (AKI), chronic kidney disease (CKD), and dialysis because of concerns regarding nephrogenic systemic fibrosis (NSF). The position that GBCA are absolutely contraindicated in AKI, category G4 and G5 CKD (estimated glomerular filtration rate [eGFR] < 30 mL/min/1.73 m2), and dialysis-dependent patients is outdated and may limit access to clinically necessary contrast-enhanced magnetic resonance imaging (MRI) examinations. This review and clinical practice guideline addresses the discrepancy between existing Canadian guidelines regarding use of GBCA in renal impairment and NSF.Sources of information:Published literature (including clinical trials, retrospective cohort series, review articles, and case reports), online registries, and direct manufacturer databases were searched for reported cases of NSF by class and specific GBCA and exposed patient population.Methods:A comprehensive review was conducted identifying cases of NSF and their association to class of GBCA, specific GBCA used, patient, and dose (when this information was available). Based on the available literature, consensus guidelines were developed by an expert panel of radiologists and nephrologists.Key findings:In patients with category G2 or G3 CKD (eGFR ≥ 30 and < 60 mL/min/1.73 m2), administration of standard doses of GBCA is safe and no additional precautions are necessary. In patients with AKI, with category G4 or G5 CKD (eGFR < 30 mL/min/1.73 m2) or on dialysis, administration of GBCA should be considered individually and alternative imaging modalities utilized whenever possible. If GBCA are necessary, newer GBCA may be administered with patient consent obtained by a physician (or their delegate) citing an exceedingly low risk (much less than 1%) of developing NSF. Standard GBCA dosing should be used; half or quarter dosing is not recommended and repeat injections should be avoided. Dialysis-dependent patients should receive dialysis; however, initiating dialysis or switching from peritoneal to hemodialysis to reduce the risk of NSF is unproven. Use of a macrocyclic ionic instead of macrocyclic nonionic GBCA or macrocyclic instead of newer linear GBCA to further prevent NSF is unproven. Gadopentetate dimeglumine, gadodiamide, and gadoversetamide remain absolutely contraindicated in patients with AKI, those with category G4 or G5 CKD, or those on dialysis. The panel agreed that screening for renal disease is important but less critical when using macrocyclic and newer linear GBCA. Monitoring for and reporting of potential cases of NSF in patients with AKI or CKD who have received GBCA is recommended.Limitations:Limited available literature (number of injections and use in renal impairment) regarding the use of gadoxetate disodium. Limited, but growing and generally high-quality, number of clinical trials evaluating GBCA administration in renal impairment. Limited data regarding the t...