Clinical context

An 8-year-old with nonresolving fever

At a glance

Stain	MGG

About B cell Acute Lymphoblastic Leukaemia

This blood film shows acute leukaemia, and a nice dimorphic population of blasts. It can be hard here to decide if these are heterogensous blasts - where they are all slghtly different, or dimorphic, where there are two separate populations. In this sample (especially given you can see the flow!), dimorphic fits better. The majority of the cells are small cells with extremely high NC ratio and open chromatin. You might be fooled into thinking these are not blasts - just lymphocytes, but the nuclear pattern is not one of a mature cell. The second population are more classical blasts. Both populations are monomorphic within themselves though- so its not heterogenous.

When trying to tell between lymphoid and myeloid, if you cant see granules or auer rods, then monomorphic is a feature of lymphoid malignancies more than myeloid. Myeloid cells tend to be more varied.

There are also on her some smear cells (more lymphoid than myeloid), and a few normal neutrophils - these are less common in myeloid malignancies. Overall, if you got acute leukaemia thats a good start.

Morphological features

Mixed Population of Leukaemic Blasts

The morphology here is difficult - it's tempting to report the blast popuation as hetergenous since there are some larger blasts with very open chromatin and smaller blasts with extremely high NC ratio. \n\nThe more you look though, the more you can convince yourself that all the blasts fit into one of there two categories. There is little nuclear heterogeneity, no features of myeloid differentiation and no auer rods.\n\nOnce you have established a diagnosis of acute leukaemia, it's always good to have a stab at lymphoid versus myeloid. The monomorphic nature of these cells (even with the dual population) is strongly suggestive of lymphoid leukaemia.

Monomorphic Small Blasts

Its always controversial discussing whether blasts are monomorphic or not.\n\nMonomorphic doesn't mean identical - it just means they have one appearance, and in this leukaemia the blast populations are monomorphic (there's just two of them). In this field, all the blasts are small, high NC ratio, open chromatin with very similar nuclear staining. There is almost no nuclear involution and they are very round.\n\nThe large population of blasts are also monomorphic.\n\nMonomorphic is a feature of lymphoid malignancies. It's not hard to think why - once a blast is committed to the lymphoid lineage (i.e. not undifferentiated/primitive) then it would normally differentiate into B lymphocytes or T lymphocytes - nothing else. Myeloid blasts would normally differentiate into everything else from megakaryocytes to erytrhoblasts and so they get more heterogeneity in their appearance as each blast undergoes abnormal attempts to mature.

Smear Cell

Smear Cells as highlighted here are a feature of all lymphoid malignancies. It's presence does not suggest low grade/CLL here!

Normal Neutrophil

Neutrophils in lymphoid leukaemia can go either way - sometimes they are the first victims and disappear from the blood before the blasts even appear (the 'aleukaemic acute leukaemia' which is well documented in children), but equally often the myeloid differentiation appears grossly unaffected and you will see relatively normal numbers of neutrophils.\n\nOne thing you shouldn't see in lymphoid leukaemia though is abnormal neutrophil morphology. The presence of pelgar forms, left shifted neutrophils or hypogranular cytoplasm should make you think about myeloid leukaemias or whether there is an underlying myeloid disorder - elderly patients could have MDS and ALL, and a proportion of CMLs transform into ALL if they do transform.

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