Multilocular Cystic Renal Tumor in Children

Radiologic-Pathologic Correlation

Abstract Introduction and Historical Background Clinical Features

Pathologic Features Radiologic Features Differential Diagnosis Treatment and Prognosis

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Pathologic Features

A solitary, well-circumscribed, multiseptated mass of noncommunicating fluid-filled loculi, surrounded by a thick fibrous capsule and compressed renal parenchyma are the gross findings in both cystic nephroma and CPDN (Figure 1, Figure 2). The mass is typically large, often replacing an entire renal pole. In the previous AFIP series, the mean size of the mass was 7.6 9.7 cm in the 30 patients who were 4 years old or younger (16).

The cyst contents are either clear-to-yellow fluid, similar to serum (23), or thick myxomatous gel (24). Cyst herniation into the renal pelvis has been described (10,16). The individual cysts vary from microscopic to 2 4 cm in diameter. Solid nodules of tissue are not discernible at gross inspection (25). Hemorrhage and necrosis are not usually found (26). Calcification is uncommon.

Although cystic nephroma and CPDN are identical in their gross anatomic features, they are distinct from each other histologically (Figure 3, Figure 4). In cystic nephroma, the cysts are lined by flattened, cuboidal, or hobnail epithelium. As defined by Joshi and Beckwith (15), the septa consist of fibrous tissue, which may contain well-differentiated renal tubules but no poorly differentiated tissues or blastemal cells. CPDN, on the other hand, has the histologic features of cystic nephroma with the addition of septal blastemal cells in any amount, with or without other embryonal stroma or epithelial cell types. Subclassification of CPDN on the basis of the relative amounts of immature tissues present has been proposed in an effort to predict the risk of aggressive behavior (Figure 5) (15): In grade 1 CPDN (relatively mature subtype), the septa contain greater than 50% mature elements. Grade 2 CPDN contains less than 50% mature septal elements.

CPDN must be distinguished pathologically from Wilms tumor, in which cysts have formed as a consequence of hemorrhage and necrosis in solid tissue. This differentiation may require obtaining thin serial sections of the entire specimen to search thoroughly for solid components.

Abstract Introduction and Historical Background Clinical Features

Pathologic Features Radiologic Features Differential Diagnosis Treatment and Prognosis

Summary Source Information References