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PA17.1 | Aplastic Anaemia & Bone Marrow Examination — Part 3

Bone Marrow Aspiration and Biopsy — Indications

Bone marrow examination encompasses two complementary procedures:
1. Bone marrow aspiration (BMA) — withdrawal of liquid marrow for cytology
2. Trephine biopsy (BMB) — core of intact marrow tissue for histology

Both are usually performed at the same sitting from the same site.

Indications for bone marrow examination:
1. Unexplained pancytopenia or isolated unexplained cytopenia (as in aplastic anaemia)
2. Suspected acute leukaemia — classification and cytogenetics
3. Suspected lymphoma — staging (Ann Arbor system) requires marrow examination
4. Suspected multiple myeloma — plasma cell percentage for diagnosis and response
5. Suspected myelodysplastic syndrome
6. Staging of solid tumours — marrow infiltration by metastatic carcinoma (breast, prostate, lung, neuroblastoma)
7. Fever of unknown origin with suspected haematological cause
8. Monitoring treatment response — post-chemotherapy, post-transplant engraftment
9. Suspected storage disorders (Gaucher, Niemann-Pick) — foam cells in marrow
10. Iron deficiency confirmation — Prussian blue stain for iron stores (rarely needed today; serum ferritin is used)

Technique and Sites

Sites for bone marrow examination:

Site	Procedure possible	Notes
Posterior superior iliac crest	Aspiration + trephine biopsy	Site of choice in adults; safe, abundant marrow, away from vital structures
Anterior superior iliac crest	Aspiration + trephine biopsy	Alternative; used if posterior site inaccessible
Sternum (manubrium)	Aspiration only	NO trephine here (risk of cardiac tamponade); still used in some centres for quick aspirate
Tibia	Aspiration in infants <1 year	Anteromedial tibia

Technique summary (posterior iliac crest):
1. Patient positioned left or right lateral decubitus
2. Site identified, cleaned, local anaesthesia to skin, periosteum, and subcutaneous tissue
3. Jamshidi needle (trephine) advanced with rotary motion through cortex into medullary cavity
4. Aspirate first (~0.5 mL only; more dilutes with blood) → smears prepared immediately
5. Trephine core taken from same site, slightly deeper; minimum 1.5 cm needed for adequacy
6. Core fixed in formalin → decalcified → paraffin sections

Four-panel medical diagram showing bone marrow biopsy techniques, microscopic comparisons, procedural capabilities, and dry tap causes. — **Panel A:** Posterior superior iliac crest anatomy, aspiration needle placement, trephine biopsy needle position, patient positioning, cortical bone, trabecular bone. **Panel B:** Bone marrow aspirate cellular morphology, trephine core biopsy architecture, individual cell detail, spatial organization, cellularity assessment. **Panel C:** Aspirate capabilities (cell morphology, blast count, M:E ratio), trephine capabilities (architecture, fibrosis detection, cellularity), respective limitations. **Panel D:** Normal marrow architecture, myelofibrosis with reticulin fibers, packed marrow with cellular infiltration, dry tap mechanism illustration.

Aspirate vs Trephine — What Each Shows

The two procedures are complementary, not interchangeable:

Bone marrow aspirate:
- Shows individual cell morphology (cytoplasmic detail, nuclear chromatin, granules)
- Used for: blast morphology and count, erythroid/myeloid ratio (M:E ratio), megakaryocyte morphology, iron stores (Perls stain), cytochemistry, immunophenotyping, cytogenetics/FISH
- Limitation: cannot show architecture (how cells are spatially organised)

Trephine biopsy:
- Shows marrow architecture — cellularity, fat-to-haematopoietic ratio, topographic distribution of cell lineages
- Detects: fibrosis (reticulin/silver stain), granulomas, metastatic deposits, focal lesions, lymphoma infiltration
- Estimates overall marrow cellularity — critical for aplastic anaemia diagnosis
- Limitation: individual cell morphology is inferior to aspirate

The 'dry tap':
When no marrow can be aspirated despite correct needle placement, this is a dry tap. Causes:
1. Myelofibrosis — fibrosis prevents aspiration
2. Packed marrow — very dense infiltration (hairy-cell leukaemia, ALL, marrow metastasis)
3. Technical failure

A dry tap mandates a trephine biopsy to determine the cause.

Side-by-side histological comparison of normal bone marrow showing 50% cellularity versus aplastic anemia showing severe hypocellularity with fat replacement. — **Panel A:** Normal bone marrow with hematopoietic islands, developing blood cells, adipose tissue, 50% cellularity annotation, 100× magnification. **Panel B:** Aplastic anemia marrow with fat replacement, sparse residual lymphocytes, absent hematopoietic elements, <10% cellularity annotation, 100× magnification.