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OVERVIEW OF RENAL CYSTIC DISEASE

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Renal cystic disease is a spectrum of genetic, developmental, and acquired abnormalities (Table 45-1). The clinical spectrum ranges from severe bilateral cystic renal dysplasia that results in death during the perinatal period to clinically inconsequential simple renal cysts. Genetic forms of cystic disease such as polycystic disease and renal cysts associated with syndromes are bilateral. Unilateral renal cysts occur with multicystic dysplastic kidney, developmental cysts, and cystic neoplasms.1–3

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Table 45–1.Renal Cystic Disease in Children
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CYSTIC RENAL DYSPLASIA

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The term renal dysplasia refers to embryonic maldevelopment of the kidney. This encompasses a varied group of malformations in which there is abnormal morphogenesis, differentiation, or structural organization of the kidney. Dysplastic kidneys may be large or small, functioning or nonfunctioning, and solid or cystic. Renal dysplasia can be diffuse or segmental. The presence of primitive structures is an important pathological feature of the various forms of renal dysplasia. Primitive ducts may be present in the medulla. Many dysplastic kidneys contain foci of cartilage. Other potential histological features include primitive glomeruli, ductules, and tubules.

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A form of renal dysplasia can occur in association with severe lower urinary tract obstruction that occurs during fetal development or early in infancy. The pathophysiology of renal involvement in this situation is similar to that of multicystic dysplastic kidney; the severity of dysplasia roughly corresponds to the severity of obstruction. The timing of the obstruction during embryological development is also important. The most common cause of this type of renal dysplasia is posterior urethral valves.

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In addition to collecting system dilation and parenchymal thinning, fetal or neonatal urinary tract obstruction can lead to the formation of multiple cysts. The cysts vary in size, but usually are less than 1 mm in diameter, that is, microcysts. Developing glomeruli in the nephrogenic zone are most susceptible to the effects of obstruction-related pressure elevation; therefore, the cysts are predominantly cortical.

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Sonography of renal dysplasia due to severe lower urinary tract obstruction demonstrates marked hydronephrosis and parenchymal thinning. The dysplastic parenchyma is hyperechoic. The dilated pelvicaliceal system often has ...

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