Primary Hematopoietic and Lymphoid Tissue ›› Bone Marrow ›› Normal

Myeloblast*


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› Microscopic Features:

• 3-4x larger than a mature RBC
• High nuclear to cytoplasmic ratio (very little cytoplasm)
• Round Nucleus with immature chromatin (not clumped)
• Prominent nucleoli
• Cytoplasm is scant, gray to pale blue and lacks granules

› Normal % blood-PB, marrow-BM, lymphoid tissue-LN:

• PB: None
• BM: Scattered (~1-3%)
• LN: None

› May Resemble:

• Promyelocyte
• Pronormoblast
• Lymphoblasts
• Immature B-cell (hematogone)
• Monoblast
• Reactive lymphocyte

› Differential Diagnoses:

If in blood or increased numbers in bone marrow: Acute myeloid leukemia (AML) Myelodysplastic Syndromes (e.g. RAEB-I or II) Myeloproliferative Neoplasms (e.g. CML with increased blasts) Leukemoid reactions Post GCSF therapy

› Classic Immunophenotype:

• CD34+
• CD117+
• HLA-DR+
• CD13+
• CD33+
• CD15-

› Cartoon Image:


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› Misc:

• Approximately 1-3% myeloblasts can be seen in a normal bone marrow but no auer rods are allowed in normal myeloblasts