Genitourinary Radiology > Kidneys > Masses > Overview

Renal Masses: Overview


Renal cysts are the most common renal mass. Cysts are ubiquitous with 50% of the population older than 50 having a simple renal cyst. Differentiating malignant from benign lesions radiographically is of utmost importance because the radiographic impression of a renal mass dictates therapy. Renal biopsies and histiological specimens have poor sensitivity and specificity for cancer.

The scheme used on this website is to divide masses by cystic vs. solid, although many other characteristics are involved in determining the true nature of a renal mass. An important differentiation is an exophytic, “ball-shaped” mass vs. an infiltrating process which maintains the kidney’s “bean-shape”. A mass that appears ball shaped grows by expansion and compresses, rather than invades, objects around it. This leads to deformation of surrounding structures. These are more easily detected radiographicly and commonly represent simple cysts, renal cell carcinoma, angiomyolipoma, abscesses, or metastases.

Lesions which maintain the kidney's bean shape grow by infiltrating the lattice of normal renal parenchymal. This results in little anatomic distortion and difficult detection by imaging.  Lesions that appear in this manner include transitional cell carcinoma, pyelonephritis, infiltrating renal cell carcinoma, lymphoma , and renal infarcts.

Calcification is a worrisome characteristic of a mass. The character and distribution of calcification is important: only 20% of masses with peripheral calcifications are renal cell carcinoma whereas 87% with central and irregular calcifications are renal cell carcinoma. The presence of fat is almost pathognomic for a bening lesion known as angiomyolipoma . Enhancement in masses following contrast administration is very worrisome and is the most predictive finding for renal cell cancer and is, in general, an indication for surgery.

© Copyright Rector and Visitors of the University of Virginia 2013