A trephine biopsy can only be graded reliably if there is enough marrow to assess. Aim for at least 1.5 cm of evaluable intertrabecular marrow, excluding cortex, cartilage and the subcortical zone, which is normally hypocellular and can mislead on cellularity. Crushed or fragmented cores make fibrosis and architecture hard to judge.
Grade fibrosis on a reticulin stain using the WHO MF-0 to MF-3 scale, assessing it in haematopoietic areas rather than around vessels. Add a trichrome stain when reticulin is MF-2 or more to look for collagen, and comment on osteosclerosis separately. If the core is inadequate, say so in the report so a repeat can be considered.
- Aim for at least 1.5 cm of evaluable marrow in the core.
- Exclude the subcortical zone when judging cellularity.
- Grade fibrosis on reticulin in haematopoietic areas using MF-0 to MF-3.
- Add a trichrome stain for collagen when reticulin is MF-2 or higher.
- State clearly when a core is inadequate for grading.
Why it matters
Fibrosis grade and cellularity drive myelofibrosis diagnosis, and both depend on an adequate core.
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