Rosai-Dorfman disease of the pleura: a rare extranodal presentation.

We present a case of Rosai-Dorfman disease (sinus histiocytosis with massive lymphadenopathy) manifesting primarily as a pleural disease without involvement of the lung parenchyma. The patient is an 81-year-old man who presented with increasing shortness of breath. Radiographic studies revealed a large loculated left-sided pleural effusion and parietal pleural thickening. Video-assisted thoracoscopic biopsy of the pleura showed the characteristic S100-positive histiocytes exhibiting emperipolesis. In this rare case of pleural Rosai-Dorfman disease, the extensive involvement of the pleural lymphatics by the characteristic histiocytes appears to have been responsible for the pleural effusion.