Renal Cysts & Polycystic Diseases Renal cysts are fluid-filled sacs that form in the kidney epithelia; they are often asymptomatic, but in some cases can cause end-stage renal failure. Simple Cysts Bosniak Grade 1 Very common and are often found incidentally – it is estimated that up to 40% of people have these renal cysts. We show a simple cyst in the periphery of the renal tissue with watery, straw-colored fluid. Simple cysts are usually acquired, and the number of cysts increases with age. They are generally asymptomatic with no malignancy potential, and do not require intervention. However, indicate that simple renal cysts can be become infected or rupture and cause hemorrhaging, and larger cysts can cause obstructive problems. Complex Cysts Bosniak Grade II Grade II cysts have very thin "hairline" septa. Grade II F (F is for follow-up) cysts have thicker walls and multiple thick septa with increasing calcification; these cysts are larger, with diameters of 3 cm or more. Grades II and IIF have low malignancy potential, but, as its name implies, Grade IIF requires follow-up due to slightly higher malignancy potential. Bosniak Grade III Grade III cysts have thick walls with multiple nodules and CT enhancement. Bosniak Grade IV Grade IV cysts comprise solid masses with cystic and necrotic components; on CT we see enhancement of the soft tissue and cystic components. Grades III and IV have increasingly higher malignancy risk, and partial or total nephrectomy is recommended. Polycystic kidney diseases Can be autosomal dominant, recessive, or sporadic (sporadic is very rare). Characterized by multiple, bilateral fluid-filed cysts caused by defects in the primary cilia of the renal tubule cells. The exact role of the primary cilia in renal cyst formation is uncertain, but it's thought to play a key role in the signaling pathways that establish and maintain functional tubule epithelium differentiation. Cysts arise from the tubule epithelial cells: the dysregulated tub...