Gallery: APL


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Abnormal promyelocyte morphology in blood

The number of abnormal cells in blood is usually low in this form and they tend to be large (though they can vary markedly in size). The cytoplasm is densely packed with red/purple granules that are large and may obscure the nucleus, although the primitive appearance of the chromatin can usually be detected, and when visible the nuclei may be seen to be indented or bilobed. In some cells rod-like structures may occur in bundles (faggot cells) although these are more often seen in marrow. Normal promyelocytes tend to have a more obvious Golgi zone, and the granules are more uniform and dispersed - remember that in blood normal promyelocytes are rarely seen, and if present a reactive or myeloproliferative cause will usually be apparent. ,

Other aspects that may be present:

Blast cell number in blood may be low, so look carefully - particularly at the edges of the film. Also look for features of any associated coagulopathy (caused by release of the abnormal granule contents with a resulting clotting factor activation). This may include fragmented or damaged red cells, and a disproportionate level of thrombocytopenia.

Large image of hypergranular APL

APL large.jpg

Image: APL cells in blood: Note the very large size of the abnormal promyelocytes and their variable appearance. Granules are prominent although less so than in many examples of APL. The presence of granules allows the appearances to be distinguished from monocytic AML (which can have similar size). The cellular background is also consistent with APL since many red cells have features of damage (including one keratocyte); platelets are absent on this image.