RESUMEN
BACKGROUND: Follicular dendritic cell (FDC) sarcoma is a rare low-to-intermediate grade malignant dendritic cell neoplasm that often has an indolent clinical course. FDC sarcomas are often misdiagnosed on aspiration cytology. CASE: A 26-year-old woman presented with a solid, slowly growing, painless mass in her right neck for 3 months. Computed tomography revealed a 3.6-cm, well-defined homogenous solid mass located posterior to the mandible and submandibular glands. Fine needle aspiration cytology revealed many large, spindle to ovoid epithelioid cells in singles, small clusters, and syncytial sheets with moderate to abundant cytoplasm, indistinct cell borders, irregular nuclear membrane, fine to vesicular chromatin, and conspicuous nucleoli. The background contained many small mature lymphocytes intimately mixed with large epithelioid tumor cells. Tumor cells were strongly positive for CD21, CD35, CD23, and fascin. Diagnosis of FDC sarcoma was rendered; follow-up surgical resection and ultrastructural study confirmed the diagnosis. The cytogenetic study showed a normal female karyotype 46,XX. CONCLUSION: Although the cytomorphology of FDC sarcoma is characteristic, a preoperative diagnosis of FDC sarcoma based on fine needle aspiration cytology is very challenging, if not impossible. Immunohistochemistry is always necessary for rendering and/or confirming the diagnosis, and ultrastructural studies are helpful.