Extramedullary haematopoiesis in the kidney

Extramedullary haematopoiesis (EMH) is the development of haematopoietic tissue outside the bone marrow and it most often occurs in the liver and spleen. Renal EMH is quite rare and there are very few case reports concerning the kidney. We describe two cases of 'renal histologically documented EMH' and, in particular, in the second of these two, the EMH tissue coexists with a clear cell renal carcinoma. Although rare, these clinical pictures raise some questions about the role of needle biopsy in the management of renal masses that present a diagnostic dilemma, especially in cases without involvement of other abdominal or intrathoracic organs.