Background: Malignant rhabdoid tumor of the kidney (MRTK) is a rare malignant neoplasm that usually presents as an abdominal mass. The histogenesis is uncertain, and cases outside the kidney have been reported. An association with separate primary tumors of primitive neuroepithelial origin occurring in the midline of the posterior or middle cranial fossa has been reported in approximately 15% of cases.
Cases: Three patients, a 7-month-old girl and two boys, aged of 6 and 2 months of age, underwent fine needle aspiration biopsy (FNAB) for the diagnosis of renal masses. In 2 cases the smears revealed round to polygonal cells, singly or arranged in irregularly shaped clusters. The neoplastic cells did not differ much in shape and exhibited clear, empty nuclei with prominent nucleoli; the cytoplasm was abundant and sometimes eosinophilic. In the remaining case the aforementioned characteristics of the nuclei and cytoplasm were not as prominent, and sheets of fibrovascular stroma, with attached neoplastic cells, were seen. Diagnosis of MRTK was suspected in every case based upon morphology and immunocytochemistry; the diagnosis was histologically confirmed in the surgical specimens.
Conclusion: MRTK may pose diagnostic problems due to its broad morphologic spectrum. Distinction from Wilms' tumor and clear cell sarcoma of the kidney is essential for therapeutic proposes. The results obtained in the FNAB study of these 3 cases demonstrate that diagnosis of MRTK may be proposed from fine needle aspiration smears using conventional methods together with ancillary ones (immunocytochemistry and electron microscopy).