Primary Hematopoietic and Lymphoid Tissue ›› Bone Marrow ›› Myeloid ›› Monocytes & Precursors ›› Normal
Monoblast
›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
- Myeloblast
- Pronormoblast
- Mature Monocyte
- Reactive lymphocyte
- 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
AML: Acute Monocytic Leukemia
AML: Acute Myelomonocytic Leukemia
Chronic Myelomonocytic Leukemia
›Classic Immunophenotype:
- CD34+/-
- CD64+
- CD4dim+
- CD14-
›Cartoon Image:
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›Misc:
Note: In Monocyte differentiated leukemias, total blast count is equal to Monoblasts + Promonocytes (since promonocytes are equivalent to blasts)