Diagnosis

Multilocular cystic nephroma

Findings

Imaging reveals a focal collection of uncomplicated cysts deforming the contour of the right kidney. The cysts do not appear to communicate with each other or with the renal pelvis. The septae between the cysts are smooth and regular. The development of obstruction in the involved kidney was secondary to the passage of a clot, noted as a filling defect on the initial CT image, distally.

The differential diagnosis of this lesion includes a cystic partially differentiated nephroblastoma (predominantly cystic Wilm's tumor), and congenital mesoblastic nephroma. The former occurs in the same age group and cannot be differentiated conclusively from a multilocular cystic nephroma by any imaging modality. The latter, a benign mesenchymal neoplasm, is usually solid (but rarely may be cystic) and detected in the first 3 months of life. Although there are other primarily cystic renal neoplasms, multilocular cystic renal cell carcinoma and cystic hamartoma of the renal pelvis, these entities are exceedingly rare in the pediatric population. Unilateral focal autosomal dominant polycystic kidney disease, also a very rare entity, could have a similar imaging appearance and family history would be vital to making this diagnosis.

Discussion

Multilocular cystic nephroma is an uncommon, usually benign, renal neoplasm characterized by a well-encapsulated mass of noncommunicating, fluid-filled locules separated by thin septations.¹ Since its initial description in 1892, a variety of terms have been applied to this lesion causing a great deal of confusion about this entity. Over the years, it has been considered a developmental lesion, a form of renal dysplasia, a hamartoma, and now, as initially, a neoplasm.²

It has a bimodal age and sex distribution, affecting boys from 3 months to 4 years of age, and women over 30 years of age.¹ The tumor usually presents as a non-painful abdominal mass in children. Gross hematuria, may be seen at all ages and is associated with herniation of tumor into the renal pelvis.¹ The tumor is usually unilateral but may be multiple and bilateral.^1,2

1. Madewell JE, Goldman SM, Davis CJ Jr., et al: Multilocular cystic nephroma: A radiographic-pathologic correlation of 58 patients. Radiology 146:309-321, 1983.
2. Eble JN, Bonsib SM: Extensively cystic renal neoplasms: Cystic nephroma, cystic partially differentiated nephroblastoma, multilocular cystic renal cell carcinoma, and cystic hamartoma of renal pelvis. Sem Diag Pathol 15(1):2-20, 1998.