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

Monoblast*


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› Microscopic Features:

• 3-4x larger than a mature RBC
• High nuclear to cytoplasmic ratio
• Round to slightly Indented Nucleus with immature chromatin (not clumped)
• Prominent nucleoli
• Cytoplasm is scant, gray to pale blue (more cytoplasm than a Myeloblast and with rare or absent granules
• vacuoles are rare but sometimes noted in cytoplasm

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

• PB: None
• BM: 1%
• LN: None

› May Resemble:

• Promonocyte [Compare]
• Myeloblast [Compare]
• Pronormoblast [Compare]
• Mature Monocyte [Compare]
• Reactive lymphocyte [Compare]
• Lymphoma cell (e.g. Leukemic phase of Burkitt)
• Carcinoma cell

› Differential Diagnoses:

If in blood or increased numbers in bone marrow: AML: Acute Monocytic Leukemia AML: Acute Myelomonocytic Leukemia Chronic Myelomonocytic Leukemia

› Classic Immunophenotype:

• CD34+/-
• CD64+
• CD4dim+
• CD14-

› Cartoon Image:


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for direct comparison
› Misc:

• Note: In Monocyte differentiated leukemias, total blast count is equal to Monoblasts + Promonocytes (since promonocytes are equivalent to blasts)