Bone marrow

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Author: Mikael Häggström [note 1]

Bone marrow aspirate showing normal "trilineage hematopoiesis":
- Myelomonocytic cells: an eosinophil myelocyte marked
- Erythroid cells: an orthochromatic erythroblast marked
- Megakaryocytic cells.

Autopsy

Microscopic evaluation

  • Confirm trilineage hematopoiesis (see image).
  • Look for apparent cellular atypia or decrease of cellular diversity.

Report

Example in a normal case:

Bone marrow from rib (or other location if applicable): Trilineage hematopoiesis. There is no evidence of malignancy.

Bone marrow aspirate

Find a location where bone marrow cells can be seen individually, preferably with minimal peripheral blood among them. Sometimes it is between trabeculae and sometimes it is in the surrounding area. Perform a differential count by counting 500 cells[1] and dividing the numbers by 5 to get their percentages. Don't count cells that don't have a cytoplasm or nucleus. If you receive several slides, count about the same number of cells from each slide, but don't count cells from slides where the cell types are more indistinct.

Bone marrow biopsy

Gross processing

  • Ensure that the biopsy is properly fixed (generally at least 2 hours).
  • Measure length and diameter of each fragment.
  • If the biopsy is received in a zinc-containing fixative, rinse it for about 2 minutes, such as placing the cassette in a container under running water (and block any sink enough so that the cassette won't float away).
  • Put in decalcifying solution, generally about 15 minutes, and palpate the specimen to check whether it is still firm. If it is, decalcify another 5-10 minutes and check again. Rather have it a little bit too soft than a little bit too firm. Be careful to follow grossing guidelines for bone marrows, since even a small aberration in the processing is likely to be noticed as creating artifacts.
Gross report example
The specimen is received in AZF solution and consists of __ core needle bone marrow biopsy fragment(s) measuring __ cm in length and 0.2 cm in diameter. The specimen is entirely submitted for microscopic examination in one cassette following decalcification.

Microscopic evaluation

Evaluate the following:

  • Adequacy: There should preferably be 5 intertrabecular spaces.
  • Cellularity: This is a rather rough estimation of the area of hematopoietic cells divided by the area of all intertrabecular matter, which otherwise mainly consists of fat cells and a small interstitial space. Areas of bone, hemorrhage or artifacts are not counted. In patients 20-80 years, the percentage should be about 100 minus age, such as 40% in a 60 year old patient.
  • Thrombopoiesis: There are normally about 3 megakaryocytes per 40x field.
  • Myeloid/erythroid ratio, usually defined as the ratio between the number of neutrophil granulocytes and precursors versus the number of erythroblasts. Depending on source, the lower limit of the normal range for this ratio bone marrow aspirate smears in adults is 1 to 2, and the upper limit is 5 to 8.[2] In histologic sections, the normal range is 1.5 – 3.0.[2] Some hematologists also include eosinophils, basophils and monocytes, as well as their precursors, in the myeloid number, but this has only a minor effect on the M:E ratio in normal individuals.[2] Still, if you are to calculate the value for a senior, check their preference first.
  • Look for any granuloma or cancer metastasis

In a bone marrow count, nucleated red blood cells count into the total percentage of cells (but does not count into percentage of white blood cells in peripheral blood).

See also

Notes

  1. For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Patholines:Authorship for details.

Main page

References

  1. Abdulrahman AA, Patel KH, Yang T, Koch DD, Sivers SM, Smith GH (2018). "Is a 500-Cell Count Necessary for Bone Marrow Differentials?: A Proposed Analytical Method for Validating a Lower Cutoff. ". Am J Clin Pathol 150 (1): 84-91. doi:10.1093/ajcp/aqy034. PMID 29757362. Archived from the original. . 
  2. 2.0 2.1 2.2 BJ. Bain (2017-02-19). Chapter 5: Pathology of the marrow. Basicmedical Key.

Image sources