![A Manual of Equine Diagnostic Procedures](/sites/default/files/styles/large/public/images/media/image/Equine%20Diag%20Schumacher.jpg?itok=R6o9cPs8)
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Bone Marrow Aspiration and Core Biopsy
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Bone marrow of horses is easily aspirated or biopsied. An aspirate biopsy is easier to obtain than is a core biopsy. Cellular morphology is easier to assess on an aspirate smear, but evaluation of marrow cellularity is more accurately evaluated with a core biopsy. The sternum is the site usually chosen for bone marrow aspiration or biopsy in horses, but the ribs or tuber coxae are also potential sites. Although an aspirate or biopsy is easily obtained from the sternum, the procedure performed at this site involves a risk of lacerating the heart if the needle is inadvertently pushed through the sternebrae. Blood for a complete blood count should always be submitted along with a bone marrow aspirate or biopsy to aid in interpreting results of microscopic evaluation of the aspirate or biopsy.
Bone Marrow Aspirate and Core Biopsies
Indications
- To investigate abnormalities of the cellular components of blood, including unexplained anemia or polycythemia, thrombocytopenia or thrombocytosis, leukopenia or leukocytosis, or abnormal morphology of blood cells because reticulocytes are not released into peripheral circulation of horses, anemia can be classified as regenerative or non regenerative only after cytologic examination of bone marrow.
- To determine body iron stores of anemic horses.
- Bone marrow core biopsies are indicated when repeated attempts at aspiration are unsuccessful. Evaluation of a core biopsy may provide more accurate information than does an aspirate biopsy concerning cellularity of bone marrow.
- For collection of marrow for administration into a damaged tendon or ligament (i.e., autologous bone marrow therapy for tendinitis and desmitis).
Materials
- Several mL of local anesthetic solution (optional)
- The procedure can be performed more safely if sedation, local analgesia, or a lip twitch, or a combination of these aids is used.
- For a bone marrow aspirate biopsy, a biopsy/aspiration needle [e.g., a Jamshidi, Illinois Sternal, JorVet or Rosenthal bone marrow needle, 15- to18-ga (1.8- to1.2-mm)] (Fig. 6-1) is used. An 18-ga, 3.5-in (1.2-mm, 8.89-cm), spinal needle is more often readily available and works well.
- For a bone marrow core biopsy, a larger biopsy/aspiration needle [8- to 11-ga (2.6 mm to 2.9 mm)] is used.
- Sterile surgical gloves, and a 12-mL or 20-mL syringe, with or without an anticoagulant (e.g., 10% EDTA or sodium citrate solution)
- Microscope slides
- 10% buffered formalin for a bone marrow core biopsy
Figure 6-1. For aspiration of bone marrow, a 15- to 18-ga. needle is used. Shown in order from left to right are: Jamshidi, JorVet, Rosenthal, and Illinois Sternal needles. Biopsy of bone marrow is performed with a larger bore (8- to 11-ga.) needle.
Bone Marrow Aspiration
Procedure
- A local analgesic agent is injected subcutaneously at the site of puncture, which is on the ventral midline, on or near a transverse line drawn between the points of the olecranons (Fig. 6-2). For tractable horses that are restrained with a lip twitch or sedation, the procedure can be performed safely without local anesthesia.
- The bone marrow needle is inserted through skin and advanced until bone is encountered (Fig. 6-3). The needle is pushed through the cortex of the sternebra by rotating the needle in an alternating clockwise and counterclockwise motion. After the needle is advanced about 1-cm, the stylet is removed from the needle, the syringe is attached, and marrow is aspirated with a sharp pull on the plunger. If blood (i.e., marrow) is not obtained, the stylet is re-inserted, and the needle is rotated and pushed deeper.
- To avoid contaminating marrow with peripheral blood, only a few drops of marrow should be collected.
- A drop of marrow is immediately (i.e., before it clots) placed on a microscope slide that is then tilted to allow contaminating blood to run off (Fig. 6-4).
- A smear is made by placing a slide over the slide on which the aspirate was placed, the blood is allowed to spread, and the slides are pulled apart in a horizontal direction (Fig. 6-5). The presence of particles on the microscope slides is evidence of a successfully performed bone marrow aspiration (Fig. 6-6).
- Alternatively, marrow can be collected into a syringe containing 1 to 2 drops of EDTA anticoagulant for transport to a laboratory for processing. It is best to quickly process marrow collected in anticoagulant (i.e., within 1 hour), because the cells quickly deteriorate.
- Unfixed, air-dried slides can be submitted to the laboratory. Several slides should be submitted, because different stains may be used to evaluate the aspirate (e.g., Romanowsky stain for morphologic evaluation, Prussian blue stain for identification of iron stores).
Figure 6-2. An 18-ga, 3.5-in (1.2-mm, 8.89-cm), spinal needle works well for aspiration of bone marrow. It is inserted into the sternum on a line connecting the points of the elbows.
Figure 6-3. By rotating the needle in an alternating clockwise and counter-clockwise motion, the needle is pushed through the cortex of the sternebra.
Figure 6-4. A drop of marrow is immediately (i.e., before it clots) placed on a microscope slide that is then tilted to allow contaminating blood to run off.
Figure 6-5. A smear is made by placing another slide over the slide on which the aspirate was placed, the sample is allowed to spread, and then the slides are pulled apart in a horizontal direction.
Figure 6-6. The presence of particles on the microscope slides is evidence of a successfully performed bone marrow aspiration.
Bone Marrow Core Biopsy
Procedure
- The procedure is nearly the same as for aspiration, except that a larger needle [8-11-ga (2.6-mm to 2.9-mm) bone marrow biopsy/aspiration needle] is used, and the stylet is removed before the needle is advanced into bone.
- The biopsy needle is advanced until bone is encountered, the stylet is removed, and the biopsy needle is rotated as it is pushed approximately 1 cm deeper.
- The needle is then removed. The stylet is pushed through the needle tip, rather than the hub, to remove the tissue specimen from the needle (Fig. 6-7).
- The specimen is placed in 10% neutral buffered formalin. (Before it is placed in formalin, it can be rolled across a glass side for cytological evaluation.)
Figure 6-7. For a bone marrow biopsy, the stylet is used to remove the tissue specimen from the needle by pushing the stylet through the needle tip rather than through the hub. The specimen is placed in 10% neutral buffered formalin.
Bone Marrow Aspirate or Biopsy
Interpretation
A clinical pathologist or clinician experienced at interpreting bone marrow aspirates should examine the aspirate. A pathologist should examine a bone marrow biopsy.
- The myloid:erythroid (M:E) ratio of normal horses ranges from 0.5 to 1.5, and the marrow reticulocyte count is normally less than 5%.
- An M:E ratio less than 0.5 indicates erythroid regeneration or myloid suppression.
- An M:E ratio less than 0.5 and a reticulocyte count >5% is characteristic of a regenerative anemia of over 5 days duration.
- Bone marrow stores of iron (observed with Prussian blue stain) are normal or increased in horses with anemia associated with chronic disease. Decreased stores of iron are seen in marrow of horses with iron-deficiency anemia.
- Most leukemias originate in the bone marrow so any indication of leukemia on the CBC (unexplained increases or decreases or morphologic abnormalities in circulating leukocytes) can be confirmed by finding neoplastic leukocytes during examination of a bone marrow biopsy.
- Thrombocytopenia caused by increased consumption (disseminated intravascular coagulation or hemorrhage) or immune-mediated destruction is usually associated with normal to increased numbers or megakaryocytes in bone marrow. Decreased numbers of megakaryocytes are seen during examination of bone marrow of horses with primary disease of bone marrow (bone marrow aplasia or neoplasia).
- Replacement of bone marrow with fat that is observed during examination of biopsies taken from at least two sites substantiates a diagnosis of bone marrow aplasia.
Complications
- Complications are very rare, but death from a needle-induced laceration of the heart can occur if the needle is accidentally pushed through the sternum. This complication can be avoided by frequent attempts to aspirate marrow as the needle is advanced into the sternebra.
Suggested Reading
Henry MM. Diagnostic approach to anemia. In: Robinson NE, ed. Current Therapy in Equine Medicine, 3rd ed, WB Saunders Co, 1992, pp 487-492.
Sellon DC, Russell KE. The when, why and how of equine bone marrow analysis. Proceedings 13th Forum American College of Veterinary Internal Medicine, 1995, pp 604-607.
Harvey JW. Atlas of Veterinary Hematology, WB Saunders Co. Philadelphia, 2001, pp 96-123.
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Affiliation of the authors at the time of publication
1College of Veterinary Medicine Auburn University Auburn, AL, USA and 2Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK, USA.
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