This marrow was done as a staging procedure for Hodgkin Lymphoma. Increasingly PET is replacing staging bone marrows for this purpose, however it is a useful opportunity to review ‘normal’ marrow tissue as Hodgkin lymphoma only occasionally results in bone marrow infiltration.  What we are seeing is emperipolesis. This means the presence of an intact cell within another cell. It commonly occurs in megakaryocytes and is a normal variant.  It can be mistaken for haemophagocytosis, but this patient clearly had no clinical evidence of this.  It can apparently be seen in hepatitis and Rosai-Dorfman disease (a histiocytic disorder), but usually it just forms the basis of a nice picture!