The Role of CT Imaging in Characterization of Small Renal Masses

Abstract

Small renal masses (SRM) are increasingly detected incidentally during imaging. They vary widely in histology and aggressiveness, and include benign renal tumors and renal cell carcinomas that can be either indolent or aggressive. Imaging plays a key role in the characterization of these small renal masses. While a confident diagnosis can be made in many cases, some renal masses are indeterminate at imaging and can present as diagnostic dilemmas for both the radiologists and the referring clinicians. This review focuses on CT characterization of small renal masses, perhaps helping us understand small renal masses. The following aspects were considered for the review: (a) assessing the presence of fat, (b) assessing the enhancement, (c) differentiating renal tumor subtype, and (d) identifying valuable CT signs.

Keywords: CT imaging; renal cell carcinoma (RCC); small renal masses (SRMs).

Figure 1

Abdominal CECT of a 77-year-old female patient: (a) the left kidney contains two cortical formations, the first in the middle-upper third (12 mm) and the second in the middle-lower third (11 mm), both with a preponderant macroscopic fat component. Both lesions show an average density lower than 20 units (−80 and −80 HU, respectively) and hence consistent with angiomyolipomas. (b) An example of a typical lipid-poor AML: the lesion is exophytic with a peculiar angular interface (red lines). Both these features help the radiologist in the diagnosis.

Figure 2

Abdominal CECT of 66 year-old male patient with a 16 mm nodular lesion in his right kidney. After the administration of contrast, the small lesion enhanced homogeneously, showing the peculiar hypervascular pattern (a) and revealing a central scar (b). These features are suitable for oncocytoma.

Figure 3

Example of endophytic malignant renal cell tumor with pseudocapsule (red arrow) at CECT in nephrographic phase (a) and urographic phase (b).

Figure 4

Abdominal CT of ccRCC: (a) in the corticomedullary phase, the lesion demonstrates an intense contrast enhancement; (b) in the excretory phase, the contrast enhancement progressively decreases.

Figure 5

Abdominal CECT of pRCC demonstrate a cortical small renal lesion. (a) In a pre-contrastographic phase, the formation is isodense with the adjacent renal parenchyma. (b) The same lesion progressively enhances homogeneously, but due to the hypovascular nature, shows overall hypoenhancement compared to the adjacent normal renal cortex.

Figure 6

Abdominal CT of an incidentally detected intraparenchymal renal lesion: (a) shows multiple macroscopic calcifications in a noncontrast CT; (b) shows that the mass is hypovascular in the arterial phase. The lesion is histologically confirmed as chRCC.

Figure 7

Another example of histologically confirmed chRCC showing (a) multiple macroscopic calcifications in a noncontrast CT and(b) the typical enhancement pattern.

Figure 8

Modified Nicolau et al. algorithm for assessment of SRMs [1].