Yves Pirson Dominique Chauveau

A kidney cyst is a fluid-filled sac arising from a dilatation in any part of the nephron or collecting duct. A sizable fraction of all kidney diseases—perhaps 10% to 15%—are characterized by cysts that are detectable by various imaging techniques. In some, cysts are the prominent abnormality; thus, the descriptor cystic (or polycystic). In others, kidney cysts are an accessory finding, or are only sometimes present, so that some question whether they are properly classified as cystic diseases of the kidney. In fact, the commonly accepted complement of cystic kidney diseases encompasses a large variety of disorders of different types, presentations, and courses. Dividing cystic disorders into genetic and "nongenetic" conditions makes sense, not only conceptually but clinically: in the former cystic involvement of the kidney often leads to renal failure and is most often associated with extrarenal manifestations of the inherited defect, whereas in the latter cysts rarely jeopardize renal function and generally are not part of a systemic disease.

In the first section of this chapter we deal with nongenetic (ie, acquired and developmental) cystic disorders, emphasizing the imaging characteristics that enable correct identification of each entity. Some common pitfalls are described. A large part of the section on genetic disorders is devoted to the most common ones (eg, autosomal-dominant polycystic kidney disease), focusing on genetics, clinical manifestations, and diagnostic tools. Even in the era of molecular genetics, the diagnosis of the less common inherited cystic nephropathies relies on proper recognition of their specific renal and extrarenal manifestations. Most of these features are illustrated in this chapter.

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