Acute myeloid leukemia (AML): Neoplastic transformation of myeloid precursors. In this case, the term myeloid refers to progeny of the multipotential myeloid stem cell, which include granulocytic, monocytic, megakaryocytic, and erythroid precursors.
Acute lymphoid leukemia (ALL): Neoplastic transformation of lymphoid precursors, which could involve B lymphocytes, T lymphocytes, or natural killer cells.
Acute lymphoid leukemia (ALL): A neoplastic proliferation of lymphoid cells which usually involves a morphologically immature lymphocyte. ALL is characterized by an acute clinical course
Adenocarcinomas: Malignant neoplasms derived from glandular epithelium.
Anaplastic: Loss of normal differentiation. Cytologically, anaplastic cells appear immature. They usually are large cells with large nuclei, finely stippled chromatin, prominent nucleoli, and moderate to marked variation in cell size, nuclear size, and N:C ratio.
Anisocytosis: Variation in cell size.
Anisokaryosis: Variation in nuclear size.
Band(ed) neutrophil (or eosinophil): A granulocyte with a nucleus that has parallel sides all around or has a nuclear indentation that is less than a third of the width of the nucleus.
Basophilia: Increase in staining with the blue dyes of the stain.
Benign: Not malignant. In general, benign cells appear less mature than their normal counterpart, but they have relatively uniform cell size, nuclear size, and N:C ratio compared to malignant cells. It is often difficult to distinguish benign neoplasia from hyperplasia based only on cytologic evaluation.
Carcinoma: Malignant neoplasm of epithelial cells.
Chromatin: The stainable portion of the DNA-protein complex in the nucleus. Chromatin patterns differ among different types of cells. Chromatin may appear minimally to markedly condensed and irregularly or evenly dispersed. Markedly condensed chromatin appears darkly stained and minimally condensed chromatin appears lightly stained. Changes in chromatin patterns are important in recognizing hyperplastic and neoplastic cells. Typically, mature, differentiated cells have condensed, evenly dispersed chromatin, whereas malignant cells have minimally condensed, irregularly dispersed chromatin.
Chronic lymphoid leukemia (CLL): A neoplastic proliferation of lymphoid cells which usually involves a morphologically mature lymphocyte. CLL is characterized by a chronic clinical course and initially, most animals are not clinically ill.
Chronic myeloid leukemia (CML): This is a very rarely recognized type of leukemia in dogs and cats. There is a neoplastic proliferation of granulocytic cells that usually maintain the ability to differentiate to mature neutrophils. CML often is a diagnosis of exclusion when other, more common causes of marked neutrophilia have been ruled out and the neutrophilia persists for months or years.
Cyclic hematopoiesis: This is a syndrome of cyclic fluctuations in blood cell counts. It has been described in grey Collie dogs and in cats with feline leukemia virus infection.
Epithelial: Pertaining to epithelial tissue.
Erythrophagocytosis: Phagocytosis of RBCs. Erythrophagocytosis usually occurs in macrophages as a result of hemorrhage or hemolysis, but also occurs rarely in neoplastic mast cells and T lymphocytes.
Erythropoiesis: The production of erythrocytes from erythroid progenitor cells.
Erythropoietin: A hormone secreted by renal peritubular interstitial cells that stimulates erythropoiesis.
Essential thrombocythemia (ET): ET is considered as a type of chronic myeloproliferative disorder and is characterized by persistent, marked thrombocytosis in the absence of physiologic or reactive causes of thrombocytosis. Platelet counts often are in excess of 1,000,000/μl.
Hematopoiesis: Hematopoiesis is the process by which undifferentiated stem cells develop into terminally differentiated cells.
Hemorrhage: Loss of blood from the vessel.
Hemosiderin: The storage form of iron in bone marrow macrophages is hemosiderin, which appears as dark brownish-green granules with Wrights stain.
Hyperplasia: Increased cell proliferation in response to irritation, inflammation, altered cellular signaling, or subsequent to tissue destruction and regeneration. Hyperplastic cells usually are larger and have less condensed chromatin and more prominent nucleoli than their normal counterpart, but their N:C ratio remains relatively constant compared to malignant cells.
Koehler illumination: Adjustment of the condenser height and iris diaphragm for optimal illumination.
Leukemia: Leukemia refers to a neoplastic proliferation of hematopoietic cells. By definition, leukemia involves the bone marrow. Leukemias often are classified by cell lineage, as myeloid or lymphoid, or by clinical course, as chronic or acute.
Leukoerythroblastic reaction: An inappropriate increase in nucleated red blood cells with a neutrophilic left shift that often indicates that there is primary bone marrow disease. The present of a leukoerythroblastic reaction is an indication for a bone marrow aspirate.
Lymphoma: Lymphoma refers to the malignant transformation of lymphoid cells which originates in tissues other than the bone marrow. The bone marrow may become infiltrated in stage V lymphoma.
Lymphopoiesis: The development of B lymphocytes, T lymphocytes, and natural killer cells from lymphoid progenitor cells. Lymphopoiesis occurs in the bone marrow but maturation of many lymphoid cells occurs in the periphery.
Malignant: Malignant cells usually appear very pleomorphic. They usually are large and have finely stippled chromatin, prominent nucleoli, and moderate to marked variation in cell size, nuclear size, and nuclear to cytoplasmic ratio.
Maturation arrest: A true maturation arrest occurs when there is disruption of differentiation to the most terminal stages for a particular cell type. An apparent maturation arrest can occur when there is depletion of the storage pool of granulocytes from rapid peripheral destruction.
Mean corpuscular volume (MCV): The mean volume of red blood cells measured in femtoliters. This value is used to determine if red blood cells are microcytic, normocytic, or macrocytic, which is part of the classification scheme for anemia.
Mean corpuscular hemoglobin concentration (MCHC): The mean hemoglobin concentration (grams) in a specific volume of red blood cells (deciliter). This value is used to determine if red blood cells are normochromic or hypochromic, which is part of the classification scheme for anemia.
Megakaryocytes: The most mature megakaryocytic cell. Megakaryocytes are very large cells with multilobed nuclei and abundant, granular cytoplasm. Platelets are produced from megakaryocyte.
Megakaryocytopoiesis: The production of megakaryocytes from megakaryocytic progenitor cells.
Megaloblastic cells: This term is used when there is asynchrony of maturation of the nucleus and the cytoplasm. Megaloblastic changes in erythroid cells are characterized by large, immature nuclei in erythroid cells with fully hemoglobinized cytoplasm and have been observed in vitamin B12 deficiency in giant schnauzer dogs and in some cats infected with feline leukemia virus.
Mesenchymal: Pertaining to connective tissue.
Metamyelocyte: A granulocyte precursor with an indented nucleus and secondary granules.
Metarubricyte: The most mature nucleated erythroid cell. It has a small nucleus with very condensed chromatin. The tinctorial quality of the cytoplasm depends on the concentration of hemoglobin.
Mitotic figure: The morphologic appearance of cells in the metaphase stage of division. The chromosomes are arranged on the equator of the spindle. Increased numbers of mitotic figures may be present in hyperplastic or neoplastic tissue.
Multiple myeloma: Multiple myeloma is a neoplastic proliferation of plasma cell that originates in the bone marrow and involves multiple bones.
Myeloblast: The most immature granulocyte precursor that is morphologically recognizable in the bone marrow. It is a large cell with fine chromatin, a prominent nucleolus, and a moderate amount of moderately basophilic cytoplasm.
Myelocyte: A granulocyte precursor characterized by a round nucleus and the initiation of secondary granule formation.
Myelodysplasia (MDS): MDS is used as a diagnosis when there are peripheral cytopenias, a hypercellular bone marrow, and blast cells are increased but less than 30% of all nucleated cells or nonerythroid cells. Morphologic abnormalities in multiple cell lines frequently are present.
Myelofibrosis: Myelofibrosis is a histologic term to indicate increased collagen in the bone marrow.
Myeloid: This term sometimes is used to refer to the bone marrow (e.g., multiple myeloma involved multiple sites of bone marrow involvement). It also is used to refer to nonlymphoid cells, in which case it includes granulocytes, monocytes, megakaryocytes, and erythroid cells (e.g., myeloid leukemia). The term "myeloid" as the numerator in the M:E ratio refers to only granulocytes and monocytes.
Myeloid to erythroid (M:E) ratio: A numerical estimate of the relative numbers of myeloid (granulocyte and monocyte) precursors and erythroid (red blood cell) precursors. Certain diseases may be associated with specific changes in the M:E ratio.
Myelophthisis: The term used to describe marked infiltration of the bone marrow by neoplastic or inflammatory cells, to the exclusion of normal hematopoietic cells. Myelophthisis can occur with hematopoietic neoplasia, metastatic neoplasia, or granulomatous inflammation.
Myelopoiesis: The production of granulocytes and monocytes from myeloid progenitor cells.
Nuclear molding: The shape of one nucleus conforms around the shape of an adjacent nucleus. Nuclear molding is a characteristic of malignant cells.
Nuclear to cytoplasmic ratio (N:C): Nuclear size compared to amount of cytoplasm. Normal lymphocytes have a high N:C ratio. Normal keratinized squamous epithelial cells have a low N:C ratio.
Packed cell volume (PCV): The volume of blood that is due to red blood cells, measured as a percentage. Usually, PCV can be used interchangeably with hematocrit. PCV is the most commonly used parameter in veterinary medicine to determine if an animal is anemic.
Pancytopenia: A decrease in all three cell lines (red blood cells, leukocytes, and platelets) in the peripheral blood.
Pleomorphic: Variation in morphologic appearance. Cytologically, pleomorphism is recognized by variation in cell size, nuclear size, and nuclear to cytoplasmic ratio.
Polycythemia vera (PV): PV is considered to be a form of chronic myelogenous leukemia in which proliferation of red blood cells predominates. It is characterized by a persistently increased red blood cell mass in the presence of normal oxygen saturation and normal or low serum erythropoietin.
Precursor cell: Morphologically recognizable hematopoietic cells that develop from lineage specific progenitors and mature into lineage restricted terminally differentiated cells. For example, myeloblasts, progranulocytes, myelocytes, and metamyelocytes are neutrophil precursors.
Primary granules: The azurophilic granules that form at the progranulocyte stage of development of myeloid cells are sometimes referred to as primary granules.
Progenitor cell: Progenitor cells have little if any capacity for self-renewal and are committed to cell production along a limited number of lineages. Lymphoid progenitor cells differentiate into B lymphocytes, T lymphocytes, and natural killer cells. Myeloid progenitor cells differentiate into granulocytes, monocytes, megakaryocytes, and erythrocytes.
Progranulocyte: A relatively immature cell in the granulocyte series that is characterized by the presence of azurophilic (primary) granules.
Prorubricyte: Rubriblasts divide and differentiate into prorubricytes, which are somewhat smaller than rubriblasts, and which have slightly more condensed chromatin. Nucleoli are absent.
Round cell tumor: Discrete cell tumors that include mast cell tumors, lymphoma, plasma cell tumors, histiocytomas, and transmissible venereal tumors.
Rubriblasts: The most immature erythroid precursor that is morphologically recognizable in the bone marrow. It is characterized by a round nucleus with minimally condensed chromatin, a nucleolus, and intensely basophilic, agranular cytoplasm.
Rubricyte: Prorubricytes divide and differentiate into rubricytes, which are somewhat small than prorubricytes, and which have moderately condensed chromatin. The tinctorial quality of the cytoplasm depends on the concentration of hemoglobin.
Sarcoma: Malignant neoplasm derived from mesenchymal tissue.
Secondary granules: The granules that develop at the myelocyte stage of development of myeloid cells are used to identify granulocytes as neutrophils, eosinophils, or basophils.
Segmented neutrophil: The most terminally differentiated cell of this series.
Spicule: A particle of bone marrow that is composed of adipocytes, hematopoietic cells, and the supportive connective tissue elements.