Background Testicular neoplasms resembling ovarian serous tumors are rarely report- ed. We describe the first fine needle aspiration biopsy (FNAB) finding of this type of tumor. Case A 35-year-old man presented with an enlarged right testis. Based on clin- ical observation, we hypothesized that it was a malignant tumor. FNA cy- tology findings revealed numerous papillary clusters, glandular-like structures and many isolated round cells. Metastatic papillary adenocarci- noma was suspected based on FNAB cytology. A right radical orchiectomy was performed, and histologic tissue examination was used to diagnose the tumor as a benign papillary serous cys- tadenoma. Conclusion Papillary serous cystadenoma of the testis is a rare tumor. The cytologic findings of this tumor are confusing and difficult to diagnose. Clusters of epithelial cells with a high nuclear to cytoplasm ratio are mistaken for fea- tures of a malignant tumor. (Acta Cytol 2009;53:467–470) Keywords: aspiration cytology, fine-needle; serous cystadenoma; testis; tumor. I t is very rare that serous tumors arise in testicular and paratestic- ular tissue. The pathogenesis of this tumor has been controver- sial. The tumors have been proposed to originate from either the mesothelium of the tunica vaginalis or vestigial remnants of the müllerian duct. Benign, borderline and malignant forms have been report-ed. 1-12 In this article we report the cytologic findings of this rare tumor. To our knowledge, this is the first report describing the cytologic features of serous cys- tadenoma of the testis by fine nee- dle aspiration biopsy (FNAB). Case Report A 35-year-old man had a history of right testis heaviness and swelling for about 6 months. The swelling then grew rapidly, and physical ex- amination revealed a solid and cys- tic mass. Based on clinical evi- dence a malignant tumor was considered. FNAB study was advised before an orchiectomy. Cytologic Findings FNA was performed by using a 20-mL syringe with a 22-gauge nee- dle. About 7 mL of light yellow fluid was aspirated from the swelling, which caused a dramatic reduction in the size of the swelling. The fluid was centrifuged, and smears were prepared from its sediment. Five smears were air-dried, and 5 were fixed in 90% ethanol. Air-dried and fixed smears were stained with Wright- Giemsa and Papanicolaou stains, respectively. The smears revealed numerous papillary clusters of epithelial cells, isolated round cuboidal cells and glandular-like structures (Figure 1A and B). Epithelial cells were round, with indistinct bor- ders, moderate acidophilic cytoplasm and high nuclear/cytoplasmic (N/C) ratio. The nuclei in these cells were round and hyperchro- matic (Figure 2A–D). No mitotic figures were seen. The smears were diagnosed as a malignant tumor that would most likely be a metastatic papillary adenocarcinoma. Histopathologic Findings On examination of cut sections, the gross specimen showed a large cystic mass that occupied the entire testis and measured 8 × 6 × 6 cm. The present case illustrates that well-formed papillary clusters can be the presenting feature of testicular serous cystadenoma in FNAB cytologic examination. A Diagnostic Pitfall of Fine Needle Aspiration Cytology in Testicular Papillary Serous Cyst Adenoma A Case Report Perikala V. Kumar, M.D., Mehdi Shirazi, M.D., and Mahmood Salehi, M.D. From the Department of Pathology, Cancer Research Institute, and Department of Urology, Shiraz Medical School, Shiraz, Iran. Dr. Kumar is Professor, Department of Pathology. Dr. Shirazi is Assistant Professor, Department of Urology. Dr. Salehi is Resident, Department of Pathology. Address correspondence to: Perikala V. Kumar, M.D., Department of Pathology, Shiraz Medical School, P.O. Box 1864, 71345 Shiraz, Iran (kumarv@sums.ac.ir). Financial Disclosure: The authors have no connection to any companies or products mentioned in this article. Received for publication October 2, 2007. Accepted for publication November 13, 2007. Case Reports 0001-5547/09/5304-0467/$21.00/0 © The International Academy of Cytology ACTA CYTOLOGICA 467 DO NOT DUPLICATE © Copyrighted Material