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

Summary Source Information References

Introduction and Historical Background

The term multilocular cystic renal tumor is currently used to categorize two histologically distinct, but grossly identical, entities: cystic nephroma and cystic partially differentiated nephroblastoma (CPDN). Numerous synonyms have been used previously for these two entities, but they have proved to be either ambiguous or misleading. Originally designated cystadenoma of the kidney by Edmunds in 1892 (1), these entities have also been called "benign multilocular cystic nephroma" (2), "polycystic nephroblastoma" (3), "differentiated nephroblastoma" (4), "well-differentiated polycystic Wilms tumor" (5), "benign cystic differentiated nephroblastoma" (6), and "cystic partially differentiated nephroblastoma" (7).

Although now considered to be neoplasms (8,9,10), multilocular cystic renal tumors have in the past been considered to be of developmental origin (11), hamartomas (12), or hamartomas with malignant potential (13). In 1956, Boggs and Kimmelstiel (2) first posited the true neoplastic nature of these lesions in a report of two cases of "so-called multilocular cyst of the kidney," each occurring in a male child less than 1 year of age, in one of which there were residual elements of metanephric blastema. These authors suggested "benign multilocular cystic nephroma" as an appropriate term for both cases. In 1977, Joshi et al (14) recognized CPDN as a distinct entity in the spectrum of infantile renal neoplasia; they preferred CPDN over other terms such as benign multilocular cystic nephroma when elements of partially differentiated and undifferentiated metanephric blastema were identified in the cyst septa.

More recently, Joshi and Beckwith (15) proposed a modification of existing terminology based on a review of extensive material accumulated at the National Wilms Tumor Study Pathology Center. In an effort to emphasize a neoplastic rather than a developmental or hamartomatous origin, they proposed the use of the term cystic nephroma to describe a multicystic tumor lacking blastemal or other embryonal elements. Second, they recommended that the term cystic partially differentiated nephroblastoma be used to denote a predominantly cystic lesion without nodular solid regions, in which the septa contain blastemal or other embryonal elements. Further, they proposed that both of these terms be subsets of a category of multilocular cystic renal tumor. This is the nomenclature emphasized in this article.

An attractive concept has been proposed in which cystic nephroma, CPDN, and solid Wilms tumor represent benign and malignant ends of a spectrum, analogous to the continuum in which ganglioneuroma, ganglioneuroblastoma, and neuroblastoma relate to each other (15). The presence of septal blastema makes CPDN potentially more aggressive than cystic nephroma, which lacks blastema. Neither, however, is frankly malignant, as is a Wilms tumor. In other words, CPDN may be regarded as a transition point between the two extremes. Other theories on the nature of these lesions suggest that both cystic nephroma and Wilms tumor arise from a common metanephric blastema antecedent but progress along separate lines (16), or that Wilms tumor is simply a precursor for CPDN (15). In addition, a so-called unitary hypothesis proposes that all cases of cystic nephroma and CPDN are merely variants of the same entity, with gradual maturation of the blastemal elements with age (17). It has been pointed out, however, that the unitary theory fails to reconcile the fact that two distinct populations of patients are affected by multilocular cystic renal tumor: young children with a 2:1 male predominance and adults with an 8:1 female predominance (18). Despite these theories, the exact relationship between cystic nephroma, CPDN, and Wilms tumor remains controversial.

A previous report from the Armed Forces Institute of Pathology (AFIP) described 61 "multilocular cystic nephromas" in 58 patients, 33 of whom were children (16). These cases had been accessioned into the radiologic pathology archives between 1952 and 1981 (16). That study included six patients, all boys younger than 15 months, who had tumors with blastema in cyst septa, thus fulfilling the criteria for CPDN. The radiologic studies available at the time were mostly confined to conventional radiography; only 17 sonographic and seven computed tomographic (CT) examinations performed with early-generation scanners were included. Since this original report, 22 additional pediatric cases of multilocular cystic renal tumor studied with modern cross-sectional imaging techniques have been accessioned to the AFIP radiologic pathology archives beginning in 1983. Of these 22 cases, five were of CPDN and 17 were of cystic nephroma. Representative examples from these cases are used in this article, which examines the clinical, pathologic, and radiologic features of multilocular cystic renal tumors manifesting during childhood and discusses their differential diagnosis, treatment, and prognosis.

Abstract Introduction and Historical Background Clinical Features

Pathologic Features Radiologic Features Differential Diagnosis Treatment and Prognosis

Summary Source Information References