It is often difficult to distinguish myelodysplastic syndrome (MDS) from severe aplastic
anemia (SAA) because both can present with profoundly hypocellular bone marrows. The
distinction matters because although both conditions are complicated by pancytopenia, the
risk of progression to acute leukemia is much greater in MDS. This chapter reexamines the
relationship between SAA and MDS. The clinical and morphological features and
pathophysiology of AA (including moderate and severe forms of acquired AA) are compared …