Follicular dendritic cell sarcoma associated with hyaline-vascular Castleman's disease.

: Follicular dendritic cell sarcoma (FDCS) of the head and neck region, associated with Castleman's disease (CD), is an extremely rare entity. To the best of our knowledge, we report the first case demonstrating the transformation of the former into the latter as documented in the same lymph node disection material. A 45-year-old female presented to our hospital with right sided neck swelling. Radiologic imaging showed a well defined 3.5 x 3.5 cm mass of soft tissue at the right side of the neck with multiple bilateral cervical lymph nodes. Excision of the right neck mass with lymph node disection was performed. Microscopic examination and immunohistochemical findings showed features of follicular dendritic cell sarcoma. The associated lymph nodes exhibited changes consistent with hyaline-vascular type CD, follicular dendritic cell hyperplasia and foci of overgrowth in which FDCS possibly evolved. This report confirms the evolving of FDCS in the setting of follicular dendritic cell hyperplasia occurring in Castleman's disease.