Myelofibrosis may be classified as ''primary'' or as secondary. Secondary myelofibrosis represents the reaction of the bone marrow stroma to a non-hemopoietic condition, such as metastatic carcinoma. Myelofibrosis that is classified as ''idiopathic'' or ''primary'' is a myeloproliferative disorder in which the fibrosis is reactive to a hematological neoplasm. The condition is neither primary nor idiopathic, but there is no satisfactory short designation. Chronic megakaryocytic myelosis comes closest to a satisfactory term but has not found widespread acceptance. Blood film features of ''primary'' and secondary cases are similar. Both may cause a leucoerythroblastic anemia with teardrop and other poikilocytes. However, there are specific abnormalities in primary myelofibrosis that indicate its myeloproliferative nature and permit a correct provisional diagnosis. They include micromegakaryocytes (Image 1, top left), ''bare'' megakaryocyte nuclei (top right), giant platelets (bottom left), and micromegakaryocytes that are budding platelets (bottom right). Dysplastic neutrophils are also indicative of primary myelofibrosis, whereas dyserythropoiesis is much less specific. ''Bare'' megakaryocyte nuclei actually have a thin rim of cytoplasm. They are not specific for a hematological neoplasm, whereas micromegakaryocytes have a high degree of specificity.