Bone Marrow MRI — Infiltration, Leukaemia & Marrow Reconversion

Bone Marrow MRI

Marrow is one of the body’s most information-rich tissues on MRI — reading its signal reveals infiltration by blood cancers long before other tests, and separates the sinister from the benign.

Normal marrow first

Marrow exists as red (haematopoietic) and yellow (fatty), and normally converts from red to yellow with age. Understanding this is essential — red marrow (and its physiological reconversion in anaemia, smoking, athletes or G-CSF) can mimic disease.

The key rule: marrow that is lower signal than adjacent muscle or intervertebral disc on T1 is suspicious for infiltration — normal marrow should be brighter (fat).

Detecting infiltration

Leukaemia: diffuse replacement of fatty marrow, low T1 — MRI can show disease and guide/target biopsy.
Myeloma: focal lesions, diffuse or “salt-and-pepper” patterns — whole-body/spine MRI is now part of staging.
Metastases: focal low-T1 deposits, often before cortical destruction.

Benign vs malignant & monitoring

Chemical-shift (in/opposed-phase) imaging helps: a benign lesion or normal marrow containing fat drops signal on opposed-phase, whereas tumour that has replaced fat does not. DWI and post-treatment change (fatty reconstitution = response) help monitor therapy. MRI also distinguishes benign osteoporotic from malignant vertebral fractures.

Reference: Vande Berg BC et al. Magnetic resonance imaging of normal bone marrow. Eur Radiol / marrow imaging reviews.

Educational summary for clinicians; correlate with haematology and biopsy. Not medical advice.