Assistant Professor of Radiology Shahid Beheshti University of Medicine Sciences Tehran, Iran
The complete characterization of an indeterminate renal mass on CT or MR images is challenging.
In patients with normal renal function, the most appropriate imaging modality to fully characterize an indeterminate renal mass is renal CT or MRI without and with intravenous contrast material.
There has been interspecialty consensus between radiologists and urologists that the following imaging features are essential reporting elements: tumor size, presence or absence of macroscopic fat, tumor characterization as solid or cystic, and tumor enhancement.
The size of the mass should be reported in three orthogonal dimensions at initial imaging. Macroscopic fat at CT is best detected on noncontrast CT images and defined as a component or focus of the mass measuring less than 10 HU. Macroscopic fat on MR images is defined as a component or focus of the mass that shows signal intensity loss after application of fat suppression or as linear or curvilinear chemical shift artifact of the second kind causing India ink (etching) artifact within or at the periphery of the mass, while the central portion of the mass matches the signal intensity of subcutaneous or visceral fat. Cystic renal masses, defined as a renal mass with greater than 75% nonenhancing components. The main strengths of imaging for clinical staging are its noninvasive nature, the wide availability of CT and MRI, the ability to measure tumor size, the detailed visualization of most of the critical landmarks for T staging, and the ability to aid in the detection of pathologic lymph nodes, venous invasion, and distant metastases.