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).

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Purpose:To determine the effect of intravenous (IV) low-osmolality iodinated contrast material (LOCM) on the development of post-computed tomography (CT) acute kidney injury (AKI), stratified by pre-CT estimated glomerular filtration rate (eGFR), in patients with stable renal function. Materials and Methods:Institutional review board approval was obtained and patient consent waived for this HIPAA-compliant, retrospective study. CT examinations performed over a 10-year period on unique adult inpatients with sufficient serum creatinine (SCr) data and stable renal function (difference between baseline and pre-CT SCr within 0.3 mg/dL and 50% of baseline) were identified. A 1:1 propensity score matched cohort analysis with multivariate analysis of effects was performed with post-CT AKI as the primary outcome measure (8826 nonenhanced and 8826 IV contrast agent-enhanced CT studies in 17 652 patients). Propensity matching was performed with respect to likelihood of receiving IV contrast material (19 tested covariates). Post-CT AKI with Acute Kidney Injury Network SCr criteria was the primary endpoint. A stepwise multivariate conditional logistic regression model was performed to identify the effect of IV LOCM on post-CT AKI. Results:After 1:1 propensity matching, IV LOCM had a significant effect on the development of post-CT AKI (P = .04). This risk increased with decreases in pre-CT eGFR (60 mL/ min/1.73 m 2 : odds ratio, Conclusion:IV LOCM is a nephrotoxic risk factor in patients with a stable eGFR less than 30 mL/min/1.73 m 2 , with a trend toward significance at 30-44 mL/min/1.73 m 2 . IV LOCM does not appear to be a nephrotoxic risk factor in patients with a pre-CT eGFR of 45 mL/min/1.73 m 2 or greater.q RSNA, 2013

Intravenous gadoxetate disodium can result in acute self-limiting dyspnea that can have a deleterious effect on arterial phase MR image quality and occurs significantly more often than with intravenous gadobenate dimeglumine.