Purpose: The purpose of this study was to compare computed tomography (CT) and magnetic resonance imaging (MRI) in terms of likelihood of providing a definitive diagnosis (DD) and a recommendation for additional imaging (RAI), when performed to evaluate indeterminate liver and renal lesions detected on ultrasound as well as in terms of impact on imaging costs.
Methods: This retrospective study was Health Insurance Portability an Accountability Act (HIPAA)-compliant and institutional review board–approved, with waiver of informed consent. We identified consecutive indeterminate liver and renal lesions detected on ultrasound that underwent contrast-enhanced CT or MRI for further characterization. Reports from follow-up studies were reviewed for whether the impression provided DD and RAI. Frequency of DD and RAI was compared between CT and MRI using the Fisher exact test. On the basis of the observed frequency of DD, anticipated imaging costs were compared in a hypothetical sample of 100 patients with indeterminate lesions between first obtaining multiphase CT for all lesions and a subsequent MRI for those lesions indeterminate on CT versus directly obtaining a multiphase MRI for all lesions.
Results: A total of 143 renal lesions were included, of which 77 and 66 underwent CT and MRI, respectively. Magnetic resonance imaging was significantly more likely than CT to provide DD (95.5% vs 77.9%; P = 0.003) and significantly less likely to provide RAI (1.5% vs 10.4%; P = 0.038). A total of 221 liver lesions were included, of which 76 and 145 underwent CT and MRI, respectively. Magnetic resonance imaging was significantly more likely than CT to provide DD (95.2% vs 71.1%; P < 0.001) and significantly less likely to provide RAI (0% vs 10.5%; P < 0.001). Across the entire study cohort, there were 13 instances of MRI recommended after an indeterminate CT and 1 case of CT recommended after an indeterminate MRI. A DD was provided in 8 of 9 instances in which MRI was performed after an indeterminate CT. However, anticipated imaging costs were higher when directly obtaining MRI for all indeterminate lesions, compared with initially obtaining multiphase CT, for both kidney ($64,739 vs $49,759) and liver ($64,739 vs. $56,975) lesions, respectively.
Conclusions: For indeterminate liver and renal lesions detected on ultrasound, MRI is more likely to provide DD and less likely to provide RAI in comparison with CT, although these differences did not result in lower anticipated imaging costs.