Evaluation of pseudoenhancement of renal cysts during contrast-enhanced CT

OBJECTIVE. The purpose of our study was to evaluate renal cyst pseudoenhanc ement during helical CT in a phantom model and in patients. MATERIALS AND METHODS. Iodine baths containing water-filled spheres and cyl inders were constructed to simulate cysts in enhancing renal parenchyma. Io dine concentration, cyst size and location, collimation, and peak kilovolta ge were varied and cyst attenuation was measured. Data were analyzed with t he mixed linear models and Mantel-Haenszel tests. Subsequently, a paired t test compared CT attenuation values before and after contrast material enha ncement in 40 patients with 68 renal cysts (radiographic stability >3 month s). RESULTS. The attenuation values of phantom cysts increased when placed in a contrast media bath (p = 0.001). The increase in attenuation values became more pronounced with increasing iodine concentrations, decreasing peak kil ovoltage, and smaller sphere sizes. In patients, mean cyst attenuation incr eased 3.4 +/- 6.2 H after administration of contrast material (p = 0.00002) . The attenuation did not increase more than 10 H in any of the 37 cysts la rger than 2 cm found in patients. Eight (26%) of the 31 cysts smaller than 2 cm found in patients increased by at least 10 H. CONCLUSION. In a phantom model, at simulated physiologic levels of renal en hancement, cysts may pseudoenhance by more than 10 H. Similarly, in patient s, cysts may also pseudoenhance; however, most pseudoenhancement does not e xceed 10 H. In patients, pseudoenhancement of at least 10 H is more likely in cysts smaller than 2 cm.