Primary Hematopoietic and Lymphoid Tissue ›› Bone Marrow ›› 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

Classic Immunophenotype:
  • CD34+/-
  • CD64+
  • CD4dim+
  • CD14-
Cartoon Image:



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