What is the most common benign renal lesion?
A renal cyst is the most common benign renal lesion. It occurs with increasing frequency with increasing age and may be seen in up to one third of adults over the age of 60. It is round or oval in shape and is composed of simple fluid with a smooth thin wall. On CT, a simple renal cyst will have fluid attenuation (0 to 20 HU) on CT, and on MRI, it will have low signal intensity on T1-weighted images, very high signal intensity on T2-weighted images, and very high signal intensity on heavily T2-weighted images relative to renal parenchyma. Simple cysts do not demonstrate enhancement.
Sometimes, a cyst can become minimally complex secondary to hemorrhage or infection. When this occurs, on CT, the attenuation of the cyst contents will be higher than that in simple cysts. On MRI, the T1-weighted signal intensity of the cyst contents will be variably increased, and its T2-weighted signal intensity will be variably decreased relative to that of simple cysts. In addition, internal septations, fluid-debris levels, calcifications, or wall thickening may also be seen. However, no enhancing components will be present