True Enhancement vs. Pseudoenhancement in Renal masses

Accurately measuring enhancement is critical for distinguishing a benign cyst from a solid neoplasm on CT.

The Rule: True enhancement requires an increase of >20 HU from the unenhanced to the nephrographic phase. An increase of 10–20 HU is considered indeterminate.

The Pitfall: Pseudoenhancement is an artifact where a small (< 1.5 cm) cyst appears to enhance due to beam-hardening and scatter from the adjacent avidly enhancing renal parenchyma. To minimize this, always measure the HU in the center of the cyst, keeping it at least 2 mm away from the wall.