Mediastinal Castleman's disease complicated by follicular dendritic cell tumour.

We describe a rare case of follicular dendritic cell tumour which had arisen over the background of hyaline vascular type of Castleman's disease at the mediastinal location. Constellation of histology and immunohistochemistry using CD21 antibody and non-reactivity to CD15, CD30, cytokeratin and epithelial membrane antigen helped us diagnose this case. The literature is reviewed, specially with reference to the genesis of follicular dendritic cell neoplasm at the backdrop of Castleman's disease and its clinical relevance.