(See also Overview of Cystic Kidney Disease.)
Acquired cysts are usually simple, ie, they are round and sharply demarcated with smooth walls. They may be solitary or multiple.
Isolated cysts are most often detected incidentally on imaging studies; they are distinguished from other cystic renal disorders and renal masses, such as renal cell carcinoma, which is typically irregular or multiloculated with complex features such as irregular walls, septae, and areas of unclear demarcation or calcification. Their cause is unknown. They are generally clinically insignificant but rarely can cause hematuria or become infected.
Multiple cysts are most common in patients with chronic kidney disease, especially patients undergoing dialysis for many years. Cause is unknown, but the cysts may be due to compensatory hyperplasia of residually functioning nephrons. More than 50 to 80% of patients receiving dialysis for > 10 years develop acquired cystic disease (with multiple acquired cysts). Usual criterion for diagnosis is ≥ 4 cysts in each kidney detected with ultrasonography or CT. This disorder can usually be differentiated from autosomal dominant polycystic kidney disease by the absence of family history and by small or normal-sized kidneys.
Acquired cysts are usually asymptomatic, but occasional patients develop hematuria, renal or perirenal hemorrhage, infection, or flank pain. Acquired cysts are significant mainly because patients have a higher incidence of renal cell carcinoma; whether the cysts become malignant is unknown. For this reason, some physicians periodically screen patients with acquired cysts for renal carcinoma using ultrasonography or CT. Cysts that cause persistent bleeding or infection may require percutaneous drainage or, rarely, partial or complete nephrectomy.