Imaging of renal masses and staging of renal tumours

Abstract

• Renal masses are a common, often incidental finding on cross-sectional imaging. • Ultrasound can readily characterize a mass as solid or cystic. • The Bosniak classification is based on CT but can equally well be applied to MRI or contrast-enhanced ultrasound. • CT is the main method for staging renal cell carcinoma (RCC), with MRI used in specific indications, such as to assess the extent of venous involvement. • Most solid renal masses are assumed to be RCC, although approximately 20% of masses under 3 cm will be benign. • The seventh edition of the American Joint Committee on Cancer TNM staging for renal cancer has been presented. • An overview of the therapeutic options for renal cancer is discussed. Renal masses are commonly encountered in adult radiological practice, with a range of appearances from entirely cystic to solid. Characterization of more complex cystic masses is a challenge, to which the now considerably refined Bosniak classification has been applied. The Bosniak classification will be discussed in detail, with the role of ultrasound, CT and MR described. Dealing with the indeterminate masses presents an additional challenge, which is greatly aided by dedicated CT and MR protocols. Benign tumours of the kidney include angiomyolipomas and oncocytomas. Prior to surgery, it is not always possible to confidently define a lesion as benign, although certain features, such as focal fat, are important. Radiology plays a vital role in imaging renal cell carcinoma (RCC). These tumours account for approximately 90% of all malignant renal masses. The incidence of RCC is increasing, which, at least in part, is a consequence of the exponential increase in cross-sectional imaging. This has resulted in the identification of many incidental tumours, which overall are of a lower stage. The epidemiology, presentation and relevance of the various surgical options will be reviewed. The imaging modalities applied to staging will be discussed, with an emphasis on multidetector CT. The TNM staging classification in its most recently revised form is described, with discussion of the challenges this presents to cross-sectional imaging. The role of ultrasound, CT, MR and positron emission tomography-CT in imaging RCC will be discussed. The use of imaging-guided needle biopsy and percutaneous ablation in the management of RCC is addressed. A brief mention is made of other cases of malignant renal masses, including transitional cell carcinoma and lymphoma.