A Japanese female in her ninth decade consulted Gifu University Hospital for a recurrent mass in her right neck. A fine needle aspiration biopsy was performed, which revealed flat clusters of atypical cells with ovoid nuclei of various sizes containing tiny granular chromatin as well as pale scanty cytoplasm, resulting in an increased N/C ratio. Some atypical cells revealed characteristically deeply convoluted nuclei. Histological examination revealed solid clusters of loosely adherent atypical cells with marked necrosis, hemorrhage and numerous mitoses. Immunocytochemistry revealed positive staining for CD21 and CD23, which led to the diagnosis of FDCS.
