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

Myeloblast with Auer Rod*


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› Microscopic Features:

• 3-4x larger than a mature RBC
• High nuclear to cytoplasmic ratio
• Round Nucleus with immature chromatin (not clumped)
• Prominent nucleoli
• Cytoplasm is scant, gray to pale blue and usually lacks granules
• One or more red-pink rod shaped structures called Auer rod(s) are noted in the cytoplasm

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

• PB: None
• BM: None
• LN: None

› May Resemble:

• Promyelocyte [Compare]
• Pronormoblast [Compare]
• Lymphoblast [Compare]
• Monoblast [Compare]
• Reactive lymphocyte [Compare]

› Differential Diagnoses:

If in blood or in bone marrow: Acute myeloid leukemia (AML) Myelodysplastic Syndromes (specifically RAEB-II)

› Classic Immunophenotype:

• CD34+
• CD117+
• HLA-DR+
• CD13+
• CD33+
• (they may have immunophenotypic aberrancies such as gain of CD56 or CD7, etc.)

› Cartoon Image:


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› Misc:

• Presence of Auer rod is diagnostic of the blasts' Myeloid origin (the only morphologic feature that could reliably distinguish a myeloblast from a lymphoblast) . Note: Other blasts (e.g. lymphoblasts) lack Auer rods