Table 7.

Mimickers

Condition	Explanation	Distinguishing features/recommendations
Osteomyelitis (Figs. 28 and 29)	Aggressive aspect	Usually involves the metaphysis in children Small/absent soft tissue component Penumbra sign* Fistulous tracts - clinical features**
Eosinophilic granuloma (EG)	Aggressive aspect	Can be very difficult or even impossible to distinguish from malignant lesions in young patients EG of the spine shows preservation of terminal end plates, disks and posterior elements (Fig. 30)
Stress lesions (Figs. 31 and 32)	-Elderly patients with insufficiency fractures , fatigue fractures	Hypointense line extending from the cortex into the medullary area on T1- and T2WI Surrounding oedema [15] , Absence of focal lesion or soft tissue mass [15]
Bone infarcts and osteonecrosis	Early osteonecrosis may result in a poorly defined region of lucency simulating a tumour in radiographs , Calcifications can simulate those of chondroid lesions	Usually manifests as a well-defined linear serpentine rim of low signal intensity on T1WI. On T2WI the rim may have low signal intensity, high signal intensity or both (“double line” sign) Chondroid lesions show peripheral lobulations with T2 hyperintensity
Myositis ossificans (Fig. 33)	Can have a disorganised amorphous bone formation similar to osteosarcoma [19, 44]	Usually separated from the cortex Evolves to mature ossification
Haematopoietic marrow (Fig. 34)	Axial skeleton, thoracic grid, pelvis and extremities of long bones can maintain areas of haematopoietic marrow even after skeletal maturity [15] (this can simulate marrow infiltration in T1WI and cause high signal on STIR)	Signal intensity > than that of muscle on T1WI Presence of microscopic fat (>50 % drop in signal in opposed-phase) [15]
Aggressive osteoporosis	Sudden immobilisation can cause bone demineralisation, with oedema mimicking diffuse tumoral infiltration	Preferential locations: subchondral bone, tendon and ligamentar insertions

*The “penumbra sign” on MRI is a rim with higher signal intensity than that of the main abscess on T1WI. It is helpful in distinguishing between subacute osteomyelitis from other osseous lesions [45]

**Rapid onset of fever, localised pain and oedema; 50 % of cases show positive blood cultures