Bone Marrow Aspiration and Trephine Biopsy

Bone marrow examination samples haematopoietic tissue from the posterior iliac crest, the preferred site in adults and children over 18 months. The aspirate yields liquid marrow for cytology, iron stain, flow cytometry, cytogenetics, molecular tests and microbiological culture. The trephine biopsy yields a core of bone and marrow for histology, assessing cellularity, architecture, infiltration, fibrosis and granulomas.

The two are used together, since the aspirate can fail (dry tap) in fibrosis, hairy cell leukaemia and packed marrow, and the core preserves architecture that the aspirate loses.

It is used when blood tests cannot give a diagnosis, to stage and monitor disease, and to assess response to treatment.

Indications.

• Unexplained pancytopenia, persistent unexplained cytopenia, or a leucoerythroblastic film.
• Suspected acute leukaemia, myelodysplasia, myeloproliferative neoplasm (including fibrosis grading), myeloma or lymphoma staging when it changes management.
• Suspected metastatic infiltration, haemophagocytic lymphohistiocytosis, or storage disease (Gaucher cells).
• Fever of unknown origin or disseminated infection: tuberculosis, visceral leishmaniasis (amastigotes in macrophages), histoplasmosis, brucellosis, salmonellosis.
• Response assessment, measurable residual disease testing, and engraftment after transplant.
• Iron stores when ferritin is unreliable and the answer changes management.

Contraindications. There is no absolute contraindication. Local infection at the site, inability to lie still, and prior radiotherapy to the site (poor sample, so another site is chosen) are relative. Thrombocytopenia and anticoagulation are not contraindications to the posterior iliac crest, and platelet transfusion is usually unnecessary. Life threatening coagulopathy and haemophilia need correction or factor cover first.

Preparation.

• Informed consent, with risks, expected discomfort and sedation options explained.
• Review of full blood count, clotting, anticoagulant and antiplatelet use, and local anaesthetic allergy.
• Lateral or prone position with the posterior superior iliac spine identified.
• Aseptic technique and skin cleansing.
• Infiltration of skin and periosteum with 1% lidocaine, usually 5 to 10 mL, within the maximum dose on the product label (about 3 to 4.5 mg/kg without adrenaline).
• Inhaled nitrous oxide 50% in oxygen is a useful self-administered option. Sedation or general anaesthesia is used in children, with agents and doses set by local sedation practice.

Technique. The aspiration needle is advanced through the cortex into the marrow cavity, felt as a give. After the stylet is removed, an initial small aspirate of 0.5 to 1 mL is drawn rapidly for morphology, to avoid haemodilution. Further aspirates are taken for flow cytometry, cytogenetics (heparin), molecular tests and culture. Smears are made at the bedside. The trephine is taken through a slightly different angle or site.

A core of at least 1.5 cm, ideally 2 cm, is needed for adequate assessment. Touch imprints of the core are useful when the aspirate is dry. The procedure takes 10 to 20 minutes.

Aspirate findings.

• Cellularity (expected cellularity is roughly 100 minus age in years, within about 20 percentage points either side), myeloid to erythroid ratio of about 2:1 to 4:1.
• Blasts under 5% in a normal marrow. Blasts of 5 to 19% suggest myelodysplasia, and 20% or more define acute leukaemia in most settings.
• Plasma cells under 5% normally, and 10% or more clonal plasma cells supports myeloma in the right context.
• Lymphocytes up to about 20% in adults.
• Dysplasia in erythroid, myeloid and megakaryocyte lines.
• Iron stores by Perls stain, and ring sideroblasts (15% or more of erythroblasts) in myelodysplasia.
• Haemophagocytosis, infiltrating tumour cells, Leishmania amastigotes and fungi.

Trephine findings.

• Cellularity, megakaryocyte number and form, and abnormally localised immature precursors in myelodysplasia.
• Reticulin and collagen fibrosis grading in myeloproliferative neoplasms.
• Lymphoid infiltrates (nodular, interstitial or paratrabecular patterns), granulomas, metastatic carcinoma or neuroblastoma, amyloid, necrosis and bone disease.
• Immunohistochemistry (CD34, CD117, MPO, CD61, CD138, kappa and lambda, CD20, CD3) and special stains (reticulin, Perls, Ziehl-Neelsen, Grocott, PAS, Congo red).

Critical findings needing immediate action. Acute leukaemia or abnormal promyelocytes, severe aplastic anaemia (cellularity under 25%), haemophagocytosis, metastatic tumour, caseating or non-caseating granulomas, and Leishmania should be telephoned to the clinician the same day.

Complications. Serious complications occur in fewer than about 1 in 1000 procedures. Bleeding and haematoma are the most common, mainly with myeloproliferative neoplasms, severe thrombocytopenia or anticoagulation. Others are pain during the procedure, vasovagal syncope, local infection, neuropathy and needle fracture. Sternal puncture carries a risk of cardiac or great vessel injury and is avoided except for rare aspirate only indications.

Aftercare.

• Firm pressure for 5 to 15 minutes (longer in coagulopathy) and a pressure dressing kept for 24 hours.
• Paracetamol 1 g orally every 4 to 6 hours, maximum 4 g in 24 hours (lower doses for weight under 50 kg, hepatic impairment or chronic alcohol use).
• Avoid strenuous activity for 24 hours.
• Return for increasing pain, bleeding, swelling, fever or numbness.

Reporting times. Aspirate cytology within 24 hours, trephine histology after decalcification in 3 to 7 days, karyotype in 7 to 14 days, and molecular results in 1 to 14 days depending on the test.

Special groups.

• Children: tibia in infants under 18 months, iliac crest in older children, always with sedation or anaesthesia.
• Older adults: osteoporotic bone is easily penetrated, and cellularity is lower.
• Obesity: a longer needle is needed.
• Pregnancy: can be performed when needed.
• Prior pelvic radiotherapy: avoid the irradiated site.