Management of Small Renal Lesions Identified on Imaging

Assessment and Characterization

The American College of Radiology recommends a dedicated multiphase contrast-enhanced CT or MRI of the kidneys to better characterize small renal lesions, as small renal masses <1.5 cm are challenging to evaluate due to partial volume averaging and pseudoenhancement on CT 1, 2
The American College of Radiology suggests that CT with and without IV contrast is preferred for initial evaluation of indeterminate renal masses, while MRI without and with IV contrast is an excellent alternative, especially for lesions <1.5 cm due to its higher specificity for small cysts 1, 2
For hyperdense lesions, MRI may better differentiate between a hemorrhagic/proteinaceous cyst and solid mass, and homogeneous high T1 signal intensity lesions with smooth borders and lesion-to-renal parenchyma signal intensity ratio >1.6 suggest benign cysts 2

Dedicated multiphase imaging will help determine if there are enhancing components in peripherally calcified lesions, and CT is superior to MRI for detecting calcifications 1, 2
Subtraction techniques on MRI can improve assessment of enhancement in intrinsically hyperintense lesions 2

The American Urological Association recommends follow-up imaging in 6-12 months for lesions <1 cm, and consideration of follow-up in 6 months if classified as Bosniak IIF 4
For Bosniak I and II cysts, no further follow-up is needed, according to the American College of Radiology 1
Renal mass biopsy can provide a definitive diagnosis in approximately 87% of cases, and is considered for indeterminate lesions, especially if suspicious for malignancy 3, 5
Active surveillance with repeat imaging is appropriate for small lesions <1 cm, according to the American Urological Association 5