Evaluation of an incidental kidney lesion

US: ultrasound; MRI: magnetic resonance imaging; CSF: cerebrospinal fluid; CT: computed tomography.
* Other than for the diagnosis of Bosniak I simple cysts, the role of US with or without contrast material in assigning a Bosniak class or assessing a kidney lesion is uncertain. Follow-up imaging with a CT or MRI should always be performed to identify additional characteristics of the lesion.
¶ Active surveillance by imaging is typically performed every 6 to 12 months and then annually for at least 5 years.
Δ The imaging modality for follow up is generally a repeat CT scan without and with iodinated contrast dedicated for characterization of a kidney lesion. Such a dedicated study should be performed regardless of the type of original imaging study.
◊ Among patients who have acute kidney injury or severely impaired kidney function with an estimated glomerular filtration rate of <30 mL/min/1.73 m², we prefer US without and with contrast or MRI without and with gadolinium for surveillance imaging. We avoid use of group I gadolinium agents among such patients.