Post-cystic Enhancement

Fluid filled structures appear echo-free or anechoic within the image, i.e. they are displayed as uniformly black. As the sound pulse travels through fluid it encounters no scattering targets. Therefore, no reflected echoes are returned to the transducer for the corresponding position in the image. Features that enable us to identify an area of fluid with confidence, include this anechoic appearance and the presence of increased through transmission. this can be demonstrated while viewing gall bladder, urinary bladder and cysts.

Attenuation within a fluid filled structure, such as this simple serous cyst (image, yellow arrow) is minimal. Since the TGC settings are calibrated to assume uniform attenuation throughout the body, there will be an area of ‘over-compensation’ distal to such a lesion, known as post cystic enhancement.

Echoes arising from tissues within this region, are thus over amplified. They will be stronger that those from adjacent areas at a similar depth, and will therefore appear brighter than similar adjacent areas within the final image.