Background: Cystic nephroma is an uncommon pediatric renal neoplasm. It needs to be differentiated from cystic partially differentiated nephroblastoma and from other renal neoplasms showing extensive cystic change. It is scantily reported in the cytology literature.
Case: A 7-month-old female with a left-sided abdominal lump was diagnosed as having cystic Wilms' tumor on computed tomography. Fine needle aspiration cytology showed cellular smears composed of monomorphic, round to oval cells, suggestive of a small round cell tumor, possibly rhabdomyosarcoma. However, histopathologic examination showed it to be a multicystic nephroma. On review of the cytologic smears, the blastemal component was absent.
Conclusion: This case highlights 1 extreme and unexpected cytologic appearance of cystic nephroma; it may result in misdiagnosis.