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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Differential Diagnosis

Four other renal neoplasms of childhood may resemble multilocular cystic renal tumors: Wilms tumor with cyst formation as a result of hemorrhage and necrosis, clear cell sarcoma, cystic variants of mesoblastic nephroma, and renal cell carcinoma. Similarly, multicystic dysplastic kidney, especially the segmental form, may be mistaken for multilocular cystic renal tumor.

Wilms tumor (nephroblastoma) is the most common renal neoplasm of childhood, and the mean age of 3 years for patients' presentation overlaps the age range of presentation for patients with multilocular cystic renal tumor. It displays evidence of cystic necrosis on CT scans less than 10% of the time (33) and rarely is predominantly cystic (Figure 12), which may belie its aggressive potential (34). Lung, liver, and abdominal lymph nodes are common sites of metastatic spread. Prognosis is based on tumor stage and the presence or absence of anaplasia, not the extent of cystic change. In the United States, surgery is the initial primary therapy for Wilms tumor, followed by chemotherapy or radiation therapy based on stage. Overall survival approaches 90%.

Clear cell sarcoma, once considered an anaplastic subtype of Wilms tumor, may contain multiple cystic spaces secondary to hemorrhage and necrosis and thus may mimic multilocular cystic renal tumors (35). It is histologically distinct from Wilms tumor, has a proclivity to metastasize to bone, and carries a poor prognosis.

Mesoblastic nephroma is the most common renal neoplasm of infancy and may be congenital. The tumor is composed of mature spindle cells that grow by infiltration, using the nephrons as a preexisting scaffold. As a result, the tumor margins are irregular and there is nephron entrapment. Complete surgical removal is usually curative. However, mesoblastic nephroma has a cellular subtype that is potentially more aggressive, and fatal local recurrence and metastatic behavior have been documented in some cases in which the tumors were incompletely resected (36,37,38,39). This cellular subtype tends to be larger and more likely to contain cystic areas of hemorrhage and necrosis (Figure 13), thus resembling a multilocular cystic renal tumor.

Renal cell carcinoma is rare in children. The age of patient presentation (mean, 10 years) is older than that for patients with Wilms tumor and much older than the typical age of presentation for patients with childhood multilocular cystic renal tumor. Therefore, it does not pose as much of a problem in differential diagnosis. However, younger patients occasionally develop renal cell carcinoma, and, as in Wilms tumor, hemorrhage and necrosis may impart a multiloculated appearance (Figure 14).

Multicystic dysplastic kidney is a developmental abnormality characterized by multiple noncommunicating cysts of variable size with no intervening normal renal parenchyma, resulting from early in utero urinary tract obstruction. It is the most common neonatal renal mass and is detected with antenatal sonography with increasing frequency (40). Contralateral genitourinary abnormalities are associated in up to 41% of patients (41), most commonly vesicoureteral reflux and ureteropelvic junction obstruction (42).

Multicystic dysplastic kidney may mimic the imaging characteristics of multilocular cystic renal tumor. Usually, the differential diagnosis poses no difficulty because, unlike multilocular cystic renal tumors, the cysts of multicystic dysplastic kidney fill the entire kidney. Furthermore, no cases of cystic nephroma or CPDN have been detected antenatally or in the newborn period, when multicystic dysplastic kidney is usually detected. Nevertheless, differentiation of multicystic dysplastic kidney from cystic nephroma or CPDN is important, since the trend in treatment of the former is conservative follow-up rather than surgical removal.

Uncommonly, the cysts of multicystic dysplastic kidney are confined to a portion of the kidney, in which case the abnormality is called segmental multicystic dysplasia (43). When this occurs, the focal cystic mass may be confused with cystic nephroma or CPDN (Figure 15, Figure 16). Segmental multicystic dysplasia is usually associated with ureteral duplication and obstruction of the upper pole moiety of the duplicated collecting system by either intrinsic narrowing or ureterocele (44). The diagnosis of segmental multicystic dysplasia is often associated, therefore, with a history of urinary tract infection.

Abstract Introduction and Historical Background Clinical Features

Pathologic Features Radiologic Features Differential Diagnosis Treatment and Prognosis

Summary Source Information References