Histopathologic pattern of hyperplasia of bone marrow hematogones (medullar b lymphoid cell precursors) occurring after treatment of idiopathic myelofibrosis

Hematogones are bone marrow precursors of B-lymphoid cells which are morphologically difficult to distinguish from blasts and/or from small lymphocytes. We report the case of a patient presenting idiopathic myelofibrosis with minimal myeloid blastic transformation causing severe pancytopenia, treated by allograft and showing in a bone marrow biopsy, a hyperplasia of B-lymphoid cells. Histopathology and immunohistochemistry identified these cells as hyperplasia of hematogones and not a transformation into lymphoblastic acute leukaemia. The cytology of a myelogram confirmed the diagnosis.