What is the critierion for enhancement in renal cysts ?
An increase in cyst attenuation from unenhanced to post-contrast phase of more than 20 HU difference. Attenuation difference of less than 10 HU is not considered enhancement, whereas 10-20 HU attenuation difference between unenhanced and post-contrast phases is equivocal.
Unenhanced and portal venous phase imaging was done.
A 12 mm renal cyst with high attenuation of internal contents (80 HU to 100 HU) which does not increase further after contrast administration, compatible with hemorrhagic contents. In the absence of further findings, this can be safely left alone.