Cystic variant of favorable-histology Wilms' tumor presenting with osteolytic metastasis to the ribs
J Bindhu1, A Imtiaz1, RV Kumar2, MDRT Thejaswini1,
1 Department of Radiotherapy, Kidwai Memorial Institute of Oncology, Bangalore, India
2 Department of Pathology, Kidwai Memorial Institute of Oncology, Bangalore, India
Department of Radiotherapy, Kidwai Memorial Institute of Oncology, Bangalore
Cystic neoplasms of the kidney presenting in childhood always present a therapeutic dilemma. Low-risk renal tumors of childhood cover a wide spectrum: cystic nephroma, cystic partially differentiated nephroblastoma and cystic Wilms«SQ» tumor. There are difficulties in differentiating these tumors on preoperative imaging. The present case presented such a therapeutic dilemma and was finally diagnosed as a cystic variant of favorable-histology Wilms«SQ» tumor with osteolytic metastasis to the ribs. The case is presented in view of its rare presentation and the therapeutic and diagnostic challenges involved.
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Bindhu J, Imtiaz A, Kumar R V, Thejaswini M. Cystic variant of favorable-histology Wilms' tumor presenting with osteolytic metastasis to the ribs.J Postgrad Med 2010;56:28-30
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Bindhu J, Imtiaz A, Kumar R V, Thejaswini M. Cystic variant of favorable-histology Wilms' tumor presenting with osteolytic metastasis to the ribs. J Postgrad Med [serial online] 2010 [cited 2020 Feb 26 ];56:28-30
Available from: http://www.jpgmonline.com/text.asp?2010/56/1/28/62436
Cystic renal tumors of childhood are relatively rare and are believed to be part of spectrum with cystic nephroma (CN) at the benign end, cystic partially differentiated nephroblastoma (CPDN) in the intermediate region and cystic Wilms' tumor (CWT) at the malignant end. ,, The discrimination of these three entities has to be based on histology as radiological findings are often inconclusive. This results in a therapeutic dilemma as CN and CPDN are benign lesions, manageable with surgery alone, not requiring preoperative chemotherapy that would be given with the presumptive diagnosis of Wilms' tumor. We present in this paper a case of cystic renal tumor which had bilateral cystic rib lesions at primary evaluation. The varied spectrum of presentation of cystic renal tumors can represent a clinical dilemma, especially when a particular case may present mixed features. Considering the considerable morbidity associated with adjuvant radiotherapy, the need for the modality should be carefully selected. In the report we would like to elaborate on the clinical diversity of cystic neoplasms and define the need for proper selection of treatment options.
A nine-and-a-half-month-old baby was referred with a postoperative histological diagnosis of CPDN for further management. This child had presented at the primary center with a history of rapidly enlarging abdominal mass and had signs of respiratory compromise. Radiological evaluation with computerized tomography scans showed a large well-circumscribed, nonhomogeneously enhancing mass lesion in the subhepatic region. The mass measured 9 × 8.1 × 10.8 cm and had multiple cystic spaces with a dominant solid component. The normal right renal parenchyma was seen splayed peripherally around the lesion. The mass was seen to cause superior displacement of the liver and anterior displacement of the pancreas. The infra-hepatic part of the inferior vena cava was compressed by the mass. A differential diagnosis of Wilms' tumor and neuroblastoma was provided. Fine needle aspiration cytology of the mass was reported as malignant round cell tumor with immunohistochemistry showing focal cytokeratin positivity. The final histopathological diagnosis at this point was considered as consistent with Wilms' tumor. Chest X-ray showed evidence of multiple irregular expansile osteolytic lesions involving the right third to sixth ribs and left sixth rib; these were not biopsied [Figure 1]. The remaining metastatic workup did not reveal any disease in the lungs or liver. A provisional diagnosis of Wilms' tumor was made and neo-adjuvant chemotherapy was initiated. The patient received nine cycles of chemotherapy with cyclophosphamide, vincristine and etoposide. Clinically, there was more than 50% regression of the abdominal mass at the end of chemotherapy and he subsequently underwent right radical nephrectomy.
The operative findings showed a well-circumscribed bosselated large (11.5 × 7.5 cm) renal mass lesion occupying the upper pole, part of the lower pole and the renal pelvis. The cut surface of the mass showed multiple closely aligned cystic spaces. A smaller solid component was also observed. The cysts ranged from 1 - 1.5 cm in diameter. The postoperative histopathology diagnosis was provided as CPDN.
In view of the rarity of the diagnosis and controversies regarding the role of adjuvant treatment for completely resected CPND, we re-evaluated the case. This involved a multidisciplinary approach with histopathological review of blocks, comparison of prior radiological information and a repeat metastatic workup. The review of the tissue blocks showed a neoplasm with features of triphasic Wilms' tumor [with blastemal, epithelial and mesenchymal differentiation] and with post-chemotherapy changes. There were focal solid areas of necrosis with hemosiderin-laden macrophages, fibroblastic proliferation and occasional multinucleated giant cells [Figure 2]. Numerous cystic spaces of varying sizes lined by low cuboidal epithelium were also seen [Figure 3]. A final diagnosis of cystic Wilms' tumor with favorable histology was made. In view of the cystic rib lesions at presentation, the case was documented as Stage IV Wilms' tumor. Hence, further chemotherapy was planned for the patient. In view of the Stage I abdominal presentation of the tumor and lack of any lung pathology, radiotherapy either in the form of flank irradiation and/or whole lung irradiation was not considered. The child is currently doing well on adjuvant chemotherapy.
Predominantly cystic renal neoplasms have always posed diagnostic dilemmas.  The major reason for this is that all three entities are very similar in their gross appearance, do not have any discernible difference in clinical presentation and are not separable by preoperative imaging studies. This problem is especially significant because of the widely different therapeutic approaches needed. While CN and CPDN are benign lesions of the kidney, cystic nephroblastoma requires a multidisciplinary approach.
Discrimination between these subtypes has to be on the basis of histology. In 1982 Joshi and Beckwith  described the criteria for the diagnosis of cystic renal tumors in childhood. In CN, the lesion is well-defined and circumscribed. It consists of cysts and septa with the cysts lined by flattened, cuboidal or hobnail epithelium and septa that may be composed of fibrous tissue containing mature tubules but no immature elements. Immature mesenchyme/epithelial tissue or blastemal cells are found in the septa of the lesions classified as CPDN. The third category, cystic variant of Wilms' tumor, contains more solid structures between the cysts which bulge into the cystic spaces and also contain blastemal/mesenchymal/epithelial elements. The latter was the picture seen on the histopathological examination of this child's resected renal lesion.
The demarcation between CPDN and CWT often presents a grey zone. There is some evidence to suggest that all three entities arise from nehprogenic nests. Wilms' tumor has occasionally been observed to occur with CN/CPDN within the same individual.  The only discriminating clinical factor is age at presentation as most patients with CN and CPDN present before one year of age,  whereas patients of Wilms' tumor are often older. The most challenging aspect of treatment planning in these patients is caused by the difficulty of a confirmatory radiological diagnosis and the fact that a misdiagnosis of CWT would result in unnecessary neoadjuvant treatment. Both CN and CPDN can be effectively managed by surgery alone. 
The postoperative diagnosis of CPDN elsewhere had to be re-evaluated for a final conclusion of cystic Wilms' tumor, favorable histology, to be arrived at. Even after the diagnosis was established, there was controversy as to the next line of management. The occurrence of bone metastasis in favorable-histology Wilms' tumor is extremely rare. Wilms' tumor typically spreads to regional lymph nodes and distant metastasis involves lung and liver. We came across only three such reports of skeletal metastasis in this category of which two had presented at relapse.  We were unable to find any documented case of favorable-histology WT with rib metastasis. Bone scan of these lesions post chemotherapy did not show any uptake, although this is not uncommon in purely lytic lesions of bone. Even though the child was diagnosed as Stage IV Wilms' tumor as per current National wilms tumor study-5(NWTS) recommendations, the patient would not require flank or whole lung irradiation.
In this case we have elaborated the difficulties in diagnosing cystic renal masses and differentiating them from variants. The rare presentation of metastasis enhances the need for a multidisciplinary team to analyze and interpret data in ambivalent cases. We advocate further collaborative studies with centrally reviewed pathology to come to a primary diagnosis and treatment options.
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