Hairy cell leukaemia is characterised by which of the following pathological features on bone marrow biopsy?

• A Hypercellular marrow with packed lymphocytes and prolymphocytes
• B Ringed sideroblasts with Prussian blue-positive granules around nucleus
• C Fibrotic 'dry tap' marrow with 'fried-egg' appearance of infiltrating cells ✓
• D Large Reed-Sternberg cells on a background of eosinophils

Explanation

In hairy cell leukaemia, tumour cells infiltrate the bone marrow and secrete reticulin fibres causing diffuse fibrosis, leading to a 'dry tap' on aspiration. Trephine biopsy shows hairy cells with abundant pale cytoplasm and widely spaced ('fried-egg') nuclei set in a fibrotic stroma — the hallmark histological pattern. BRAF V600E mutation is pathognomonic. Ringed sideroblasts are seen in myelodysplastic syndrome; RS cells define Hodgkin lymphoma.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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