INTRODUCTION
Kidney cysts result from genetic or nongenetic processes and occur in a variety of diseases in adults and children. The most common causes of radiologically evident kidney cysts in adults are simple kidney cysts, which will be discussed in this topic review. Autosomal dominant polycystic kidney disease (ADPKD) is discussed elsewhere. (See "Autosomal dominant polycystic kidney disease (ADPKD): Kidney manifestations" and "Autosomal dominant polycystic kidney disease (ADPKD): Treatment".)
Smaller cysts, usually <1 cm in diameter, also occur in medullary sponge kidney, autosomal recessive PKD, and autosomal dominant tubulointerstitial kidney disease (previously called medullary cystic kidney disease). (See "Medullary sponge kidney" and "Autosomal recessive polycystic kidney disease in children" and "Autosomal dominant tubulointerstitial kidney disease".)
Other unusual causes of kidney cysts in adults are von Hippel-Lindau disease, tuberous sclerosis complex, Fabry disease, and nephronophthisis. (See "Clinical presentation, diagnosis, and surveillance of von Hippel-Lindau disease" and "Kidney manifestations of tuberous sclerosis complex", section on 'Kidney cysts' and "Fabry disease: Clinical features and diagnosis", section on 'When to suspect Fabry disease' and "Genetics and pathogenesis of nephronophthisis", section on 'Pathogenesis'.)
An overview of the kidney cyst classification system, our recommended approach to complex kidney cysts in adults, and a discussion of simple kidney cysts are presented in this topic review. The evaluation of a solid kidney mass is discussed separately. (See "Diagnostic approach, differential diagnosis, and management of a small renal mass".)
GENERAL PRINCIPLES
Types of kidney cysts — Kidney cysts are categorized as simple or complex. Simple kidney cysts are commonly observed in normal kidneys, with an increasing incidence as individuals age [1] (see 'Simple kidney cysts' below). They are benign, asymptomatic lesions that rarely require treatment. By contrast, complex cysts may require follow-up imaging, biopsy, or surgical excision for diagnosis and management.
