Bone-marrow aspiration and biopsy principles — branching viva

Branching viva — bone marrow aspiration and biopsy

The examiner releases the stem and then branches into four probes. A strong candidate names the two samples first, defends the site and the technique, and interprets the dry tap and the bleeding risk without prompting. [1] [2]

Opening (examiner)

"A six-year-old is referred with a haemoglobin of 60, a platelet count of 20, and blasts on the peripheral film. You plan a bone marrow aspirate and trephine. What samples will you take, and why both?" [1]

Branch 1 — The two samples (expected answer)

The aspirate is liquid marrow drawn from the medullary sinusoids and answers questions about cells as individuals: morphology, flow cytometry, cytogenetics, molecular and culture. The trephine is a core of bone that preserves the architecture and is the only sample that shows overall cellularity, fibrosis, granulomas and infiltration. Both are taken at the same sitting so the child is not brought back twice, and each fails where the other succeeds. [2]

Probe. "Why is the trephine essential in aplastic anaemia?" — Because cellularity under 25 per cent defines severe aplastic anaemia, and a liquid aspirate taken from a surviving pocket of marrow can look deceptively normal. [1] [10]

Branch 2 — Site and technique (expected answer)

Site: the posterior superior iliac spine, one to two centimetres below and lateral to the spine, where the bone is broadest and flattest and far from any vital structure. The sternum is avoided in young children because the thin cortex admits the needle into the mediastinum. Aspirate before the trephine, because the trephine disrupts the marrow and dilutes the aspirate; take the trephine from the same skin puncture but a slightly different track. [1] [2]

Probe. "You cannot aspirate marrow — is the procedure failed?" — No. A dry tap is a sign of fibrosis or a packed marrow; take a trephine, which shows the cause.

Probe. "Which pull do you send for morphology and cytogenetics?" — The first pull. It is the only one not diluted by peripheral blood, and a paediatric ALL study showed the technique can change the measured blast percentage and shift therapy stratification. [4]

Branch 3 — Analgesia and sedation (expected answer)

The periosteum is innervated, so local anaesthetic must reach it: infiltrate lidocaine one per cent into the skin, subcutaneous tissue and periosteum at 3 mg per kilogram plain or 7 mg per kilogram with adrenaline. Add procedural sedation — ketamine with midazolam, or an alfentanil–remifentanil–midazolam regimen — with monitoring and a reversal agent to hand. [7]

Probe. "The candidate suggests restraint alone — why is that not acceptable?" — Because the procedure is genuinely painful and the periosteum is innervated; adequate local anaesthetic plus sedation is the humane and the safe standard. [7]

Branch 4 — Bleeding risk and staging (expected answer)

The trephine bleeds more than the aspirate, and the thrombocytopenic, coagulopathic child needs blood-product cover first: transfuse platelets to keep the count above 20 to 50, and above 50 when also coagulopathic. A CT-guided biopsy series confirms the procedure is safe when the count and clotting are corrected. [11]

Probe. "The child is being staged for a solid tumour — how does the marrow sampling change?" — Bilateral trephines, because a unilateral biopsy can miss focal marrow disease. Missing a deposit understages the tumour and undertreats the child. [1]

Examiner's wrap

Outcome is driven by the underlying diagnosis, but the marrow examination secures it. Hold the two-samples-one-site principle, reserve the first pull for morphology and cytogenetics, and treat a dry tap as a sign that demands a trephine. The powered OnControl drill gives comparable or better trephine quality than the manual Jamshidi with less operator fatigue, and is increasingly used in older children and adolescents.