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

Immature T-cell precursor*






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:



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