Bone Marrow

• tissue enclosed by bone (cortical and cancellous)
• hematopoietic cells, adipose tissue and supportive tissue
• red and yellow (all red early in life)

• hematopoiesis.  
• All is red in young animal, turns yellow with age.  
• Adults, can be found in proximal humerus, femur, sternum, ribs, vertebral bodies

mainly fatty tissue, no hematopoietic function.  Can turn red if needed.

• precursers to cells found in blood or tissue
• includes cells in mitotic (proliferation) pool and post-mitotic (maturation) pool
• Includes erythrocytes, leukocytes, megakaryocytes

• Hematologic abnormalities (nonregenerative anemia, penias, persistent cytosis', abnormal blood cell morphology, unexplained presence of immature cells and regenerative or not in a horse.)
• What stage cancer is in (Lymphoma, mast cell tumors)
• Blood chemistry abnormalities (hyperglobulinemia, hypercalcemia)

• aspirate is easier/faster/cheaper (just stain and examine)
• biopsy cuts a solid core of marrow, has to be fixed, decalcified, embedded, sectioned and stained prior to examination by a pathologist.  More accurate evaluation.

• don't use in patients with bleeding problems (hemostatic diathesis).  Could be hemorrhage.
• Ribs and sternum of horse can lead to hemothorax or cardiac tampanade (pressure on heart)
• Post biopsy infection

• proximal humerus
• Trochanteric fossa of proximal femur
• iliac crest

Proximal femur and proximal humerus

Ilium, ribs, sternum

• General anesthesia or sedation, local anesthetic (both skin and periosteum)
• skin incision
• needle cuts through muscle
• Rotate needle into bone
• remove stylet
• attach syringe, pull back just until you see marrow (release quickly to avoid blood contamination)
• prepare smears immediatly

• drop of marrow, spread with another slide
• place vertically on absorbant surface to further remedy blood contamination
• air dry, stain with Romanowsky (Wright-type)

Jamshidi needle, stylette, shepherds crook

• Rubriblast
• prorubricyte
• rubricyte
• metarubricyte
• prolychromatophilic erythrocyte (reticulocyte)
• mature erythrocyte

most immature recognizable RBC

between rubriblast and rubricyte.  Cytoplasm more abundant and blue

between prorubricyte and metarubricyte.  Most mature stage where mitosis can occur

most mature RBC that contains a nucleus

reticulocyte.  Anucleated, blue-pink, larger than RBC

• get smaller
• nuclei gets smaller, chromatin clumps
• nucleus extruded
• cytoplasm goes from blue-grey to orange-red as RNA is lost
• reticulocytes and RBCs migrate
• Takes 3-5 days.

released from kidney in response to hypoxia.  Stimulates stem cell differentiation into rubriblast.  High enough concentration shortens marrow transit time and graduates early

androgens, glucocorticoids, insulin, growth hormone, thyroid hormone

estrogen

• Polymorphonuclear leukocytes (PMNs)
• Includes all three granules--neutrophils, basophils, eosinophils

• Same for neutrophil, basophil and eosinophil
• myeloblast
• progranulocyte (promyelocyte)
• myelocyte (first differentiation)
• metamyelocyte
• band granulocyte
• segmented granulocyte

earliest recognizable myeloid cell. No granules.  Before promyelocyte (progranulocyte)

• slightly larger than precurser myeloblast.  Also larger than follower myelocyte
• Nucleus is central or on one side (eccentric)
• cytoplasm has primary granules.

• smaller than precurser promyelocyte, larger than metamyelocyte.  
• Last mitosis
• primary granules replaced by secondary (specific) granules

• smaller than precurser myelocyte, larger than follower band granulocyte.  
• kidney shaped indention in nucleus.  Secondary granules.

• smaller than metamyelocyte, larger than segmented granulocyte.  
• U-shaped or deeply indented nucleus.  Secondary granules

smaller than band.  Lobulated or markedly constricted nuclei, secondary granules.

• difficult to differentiate because nucleus can look like anything and resembles myeloid series.
• monoblast, promonocyte, monocyte in bone marrow

• large multinucleated cell whose cytoplasmic fragments become platelets.
• megakaryoblast, promegakaryocyte (nucleus separates), megakaryocyte.

• RBC, monocytes, neutrophils
• lymphocytes (small)
• plasma cells (differentiated lymphocyte that produces hemoglobin)
• lymphoblast (rare, lymphoproliferative disorders)
• macrophages, osteoblasts, osteoclasts,

similar to plasma cells in appearance.  In young animals and those with bone remodeling (fracture)

• large multinucleated cell with nucleus separated.  
• phagocytize bone.  
• rare.

• easily recognized.  
• normally present in very low concentration, rare in marrow.

seen infrequently because don't exfoliate easily.

• scan: whole slide for heterogenous and overall cellularity
• erythroid.  
• cellularity: (25-75% cells), otherwise hyper- or hypocellular.  Decreases with age.  Increases with need.  
• Maturation/morphology: of RBC and WBC (complete, orderly, increase in # with each stage of development
• Myeloid  to Erythroid ratio (M:E): examine 500 cells, granulocytic/nRBC (hemodilution a problem)
• Reticulocyte couont in horses

myeloid to erythroid ratio.  normal is anywhere form 0.5:1 to 3:1.  Interpret in light of CBC.

mature cells, due to mitosis

high level of granulocytes or low level of erythrocytes

low level of granulocytes or high level of erythrocyes

• transient, usually stem cell recovers (if no complications)
• Initial neutropenia, thrombocytopenia and nonregenerative anemia may follow if disorder lasts for 1-2 weeks.  
• Caused by viral (F. panleukopenia or parvo), drugs (like chemo), chemicals

• irreversible, cause not always understood.  Can be chemicals or radiation, or FeLV.  
• 4 types.  Aplasia or hypoplasia, myelodysplasia, myeloproliferative disease, myelodysplasia becoming cancer.

• aplasia or hypoplasia (absent or insufficient production)
• myelodysplasia (abnormal development)
• myeloproliferative disease (neoplastic production)
• myelodysplasia progressing into neoplasia over time.

• irreversible stem cell injury with hypocellular to acellular marrow.  
• Presents with selective, severe and nonregenerative anemia or pancytopenia (nonregen anemia includes thrombocytopenia and neutropenia)
• Red cell aplasia in dogs likely immune mediated.

• abnormal development with variable manifestations of subtle, morphological changes in blood cells.  
• Usually includes some kind of cytopenia (neutropenia, nonregenerative anemia, thrombocytopenia)
• Most common in cats, very rare in others

• scarring of bone marrow, develops in response to marrow injury.  
• Can be caused by anything toxic to hematopoietic cells--damages microvasculature and leads to necrosis and fibrosis (dying and scarring)

• neoplastic proliferation of hematopoietic cells within marrow.  
• Neoplastic cells found in peripheral blood or bone marrow.

neoplasms derived from bone marrow erythrocytes, granulocytes, monocytes and megakaryocytes.  (monocytic leukemia, eosinophilic leukemia, etc.)

• neoplasms from lymphocytes or plasma cells.  
• More immature than mature cells is bad.  
• ex. acute lymphoblastic leukemia, chronic lymphocytic leukemia, plasma cell myeloma.

• Infiltration and replacement of marrow by blast cells that proliferate but do not mature or function in any useful way.  
• any hematopoietic cell line can be involved.  
• progression is rapid (death within days or weeks without bone marrow transplant)

• some infiltration of marrow.  Malignant cells mature partially and retain some function.  
• Affected can survive months to years with little/no treatment.  Don't notice right away, much better prognosis.