In general lymphoblasts may vary from very small blasts (with a high nucleus-cytoplasm ratio) with very dense chromatin, indistinct nucleoli and scant basophilic cytoplasm, to larger blasts with more finely dispersed chromatin, prominent nucleoli and a moderate amount of light blue cytoplasm. Nuclei can be round, irregular or convoluted, cytoplasmatic vacuolisation can be present. Granules are rarely present.
B-ALL and T-ALL are indistinguisable by morphology.
Flow cytometry in general: CD45+(weak), cyCD79a+, CD19+, HLA Dr+; CD10, TdT, CD34, CD20, cytoplasmic IgM and surface IgM depending on subtype.