Hematology and Clinical Microscopy Glossary - College of American ...
Hematology and Clinical Microscopy Glossary - College of American ...
Hematology and Clinical Microscopy Glossary - College of American ...
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plasma cells. Binucleated <strong>and</strong> multinucleated<br />
forms may be frequent <strong>and</strong>, when present, <strong>of</strong>ten<br />
displayimmature nuclear characteristics. Malignant<br />
plasma cells may be seen in the peripheral blood in<br />
plasma cell leukemias.<br />
Prolymphocyte<br />
Prolymphocytes are larger lymphoid cells that are seen<br />
in cases <strong>of</strong> chronic lymphocytic leukemia (CLL), where<br />
they usually comprise less than 10% <strong>of</strong> lymphoid cells.<br />
They can also be found in prolymphocytic<br />
transformation <strong>of</strong> CLL, <strong>and</strong> B <strong>and</strong> T-cell prolymphocytic<br />
leukemia (PLL). These round to ovoid cells range from 10<br />
to 18 μm <strong>and</strong> the N:C ratio varies from 5:1 to 3:1. They<br />
are larger than normal lymphocytes <strong>and</strong> the typical CLL<br />
cells <strong>and</strong> are similar in size to lymphoblasts. A centrally<br />
placed, oval to round nucleus, <strong>and</strong> a moderate<br />
amount <strong>of</strong> homogeneously staining, blue cytoplasm are<br />
typical. The cytoplasm is more abundant than in normal<br />
lymphocytes <strong>and</strong> blasts <strong>and</strong> may contain a few<br />
azurophilic granules. The nucleus shows somewhat<br />
condensed chromatin (coarser than inlymphoblasts<br />
<strong>and</strong> more open than in mature lymphocytes) with<br />
indistinct parachromatin <strong>and</strong>, typically, a single,<br />
prominent nucleolus. Occasionally, these cells may<br />
exhibit more than one nucleolus.<br />
Megakaryocytic Cells<br />
<strong>and</strong> Platelets<br />
Megakaryocyte Nucleus<br />
After discharging their cytoplasm to form platelets,<br />
megakaryocyte nuclei or nuclear fragments may enter<br />
the peripheral blood stream, particularly in conditions<br />
associated with marrow myel<strong>of</strong>ibrosis. The cell nucleus is<br />
single-lobed or less commonly, multilobated. The<br />
chromatin is smudged or “puddled” <strong>and</strong> is surrounded<br />
by a very scant amount <strong>of</strong> basophilic cytoplasm or no<br />
cytoplasm at all. If a small amount <strong>of</strong> cytoplasm is<br />
present, it is <strong>of</strong>ten wispy, frilly, or fragmented. Rarely,<br />
there may be a few localized areas <strong>of</strong> cytoplasmic<br />
blebs or adherent platelets. Small cells with more<br />
abundant cytoplasm are best termed<br />
micromegakaryocytes. If the nuclear characteristics are<br />
not appreciated, megakaryocyte nuclei may be<br />
mistakenly identified as lymphocytes. Finding<br />
megakaryocyte cytoplasmic fragments <strong>and</strong> giant<br />
platelets in the field are helpful clues to the origin <strong>of</strong> the<br />
nucleus. It is important to remember that these cells are<br />
not degenerating cells <strong>and</strong> therefore, the chromatin<br />
Blood Cell Identification<br />
pattern does not have the characteristics <strong>of</strong> basket<br />
cells. For CAP pr<strong>of</strong>iciency testing purposes,<br />
megakaryocyte nuclei are almost always seen in the<br />
blood, whereas micromegakaryocytes may be seen in<br />
blood or marrow.<br />
Megakaryocyte or Precursor, Normal<br />
Megakaryocytes are the largest bone marrow<br />
hematopoietic cell. They are derived from bone<br />
marrow stem cells <strong>and</strong> are responsible for platelet<br />
production. During development, the cell does not<br />
divide, but instead the nucleus undergoes nuclear<br />
replication without cell division (endomitoisis or<br />
endoreduplication) giving rise to a hyperdiploid nucleus<br />
with several lobes <strong>and</strong> each lobe roughly containing a<br />
normal complement <strong>of</strong> chromosomes. The cytoplasm<br />
becomes granular <strong>and</strong> eventually fragments into<br />
platelets. The nucleus is left behind to be phagocytized<br />
by marrow histiocytes. For pr<strong>of</strong>iciency testing purposes,<br />
the term normal megakaryocyte almost always refers to<br />
a mature cell rather than one <strong>of</strong> the maturation stages.<br />
Typically, the mature megakaryocyte measures at least<br />
25 to 50 μm in diameter. The numerous nuclear lobes are<br />
<strong>of</strong> various sizes, connected by large b<strong>and</strong>s or fine<br />
chromatin threads. The chromatin is coarse <strong>and</strong><br />
clumped to pyknotic. The abundant cytoplasm stains<br />
pink or wine-red <strong>and</strong> contains fine azurophilic granules<br />
that may be clustered, producing a checkered pattern.<br />
Megakaryocyte or Precursor,<br />
Abnormal<br />
Megakaryocytic dysplasia may manifest as<br />
abnormalities in cell size, nuclear shape, <strong>and</strong> cell<br />
location. Micromegakaryocytes, also known as dwarf<br />
megakaryocytes, are abnormally small megakaryocytes<br />
that usually measure 20 μm or less in diameter. The N:C<br />
ratio is 1:1 or 1:2. The nucleus may be hypolobated or<br />
may have multiple small lobes reminiscent <strong>of</strong> the PMNs<br />
in megaloblastic anemia. The cytoplasm is pale blue<br />
<strong>and</strong> may contain pink granules. Micromegakaryocytes<br />
may be found in the marrow or circulating in the<br />
peripheral blood. Larger abnormal megakaryocytes are<br />
highly variable in morphology. Some show increased<br />
nuclear lobation, while others are hypolobated or<br />
mononuclear. Normal megakaryocyte nuclei are<br />
connected in series. Dysplastic nuclei may be separated<br />
or form masses <strong>of</strong> chromatin <strong>and</strong> nuclei. The finding<br />
<strong>of</strong> triple nuclei may be a particularly useful marker<br />
<strong>of</strong> dysplasia. Pyknotic megakaryocytes are also<br />
abnormal. The naked or near-naked nuclei are<br />
composed <strong>of</strong> dark masses <strong>of</strong> chromatin. These cells are<br />
undergoing apoptosis (programmed cell death). On<br />
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