Kidney cysts, or renal cysts, are extremely common, with their prevalence increasing with age. Simple renal cysts are benign, fluid-filled sacs that meet strict ultrasound criteria: anechoic contents, a thin, smooth wall, posterior acoustic enhancement, and no internal septations, calcifications, or solid components. Cysts that have any complex features, such as internal echoes, septations, thickened walls, or solid elements, require further evaluation, often using the Bosniak classification system, which grades cystic renal lesions from I (simple, benign) through IV (clearly malignant). Most simple kidney cysts are incidental findings that require no treatment or follow-up.
Sonography Term