Case Number : CASE 4612 - 18 March 2025 Posted By: Admin_Dermpath

Rosai Dorfman disease / emperiopolesis 

Yeahh. RDD. Amazing example. 

How can RDD be distinguished from a solitary reticulohistiocytoma?

On 31/03/2025 at 11:12, Richard Logan said:

How can RDD be distinguished from a solitary reticulohistiocytoma?

Maybe a uniform appearance in different fields in RH, instead of light and dark stripes ( histiocyte and plasma cells ) of RDD, and the typical ground glass appearance of RH-histocytes. But this is just my personal impression. 

On 03/04/2025 at 14:28, vincenzo said:

Maybe a uniform appearance in different fields in RH, instead of light and dark stripes ( histiocyte and plasma cells ) of RDD, and the typical ground glass appearance of RH-histocytes. But this is just my personal impression. 

Thanks, Vincenzo.

Yes. It is a case of primary cutaneous RDD. The S-100 immunostain highlights the emperipolesis, which might not be evident on H&E, particularly in cutaneous RDD. 

On 03/04/2025 at 18:58, vincenzo said:

Maybe a uniform appearance in different fields in RH, instead of light and dark stripes ( histiocyte and plasma cells ) of RDD, and the typical ground glass appearance of RH-histocytes. But this is just my personal impression. 

Thanks for pointing out light and dark appearance which is good clue in RDD. 

On 31/03/2025 at 14:42, Richard Logan said:

How can RDD be distinguished from a solitary reticulohistiocytoma?

RDD histiocytes usually have pale feathery cytoplasm. On the contrary, the histiocytic cells of reticulohistiocytoma typically have oncocytic/ground glass cytoplasm, which is two-toned, i.e., more purplish in the center close to the nucleus and light pink peripherally close to the cell membrane.