Cytopathology of follicular dendritic cell tumors.

Follicular dendritic cell tumors are rarely described entities, arising from antigen-presenting immune accessory cells, found within B-lymphocyte follicles in nodal and extranodal sites. We report two cases, one associated with Castleman's disease, in whom fine-needle aspiration biopsy was performed followed by surgical biopsy. The diagnosis was confirmed using immunoreactivity with CD21 and CD35 antibodies and by ultrastructural demonstration of interdigitating cell processes with desmosomes. Both the cytologic and histologic findings are presented, and the differential diagnoses are discussed. Awareness of this entity and recognition of the pathologic features may lead to a presumptive diagnosis which must be confirmed using imunohistochemistry and/or electron microscopy.