Immature T-cell precursor

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Primary Hematopoietic and Lymphoid Tissue ›› Bone Marrow ›› Lymphoid ›› T-cells ›› Normal

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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, light blue and lacks granules

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

PB: None
BM: Rare (~1%)
LN: None

›May Resemble:

Myeloblast
Pronormoblast
Immature B-cell (hematogone)
Monoblast
Prolymphocyte
Reactive lymphocyte

›Differential Diagnoses:

If in blood or increased numbers in bone marrow:
T-Lymphoblastic leukemia (T-ALL)
Rarely some non-neoplastic conditions

›Classic Immunophenotype:

CD3+ (cytoplasmic)
CD7+

›Cartoon Image:

Click and drag Red blood cell for scale

for direct comparison

›Misc:

Very immature cells cannot be reliably distinguished from each other based on morphology alone. The exception are blasts with Auer Rod(s) which are unique to abnormal Myeloblasts and abnormal promyelocytes as noted in APL