Rind sign
Definition
Thick, relatively uniform sclerotic shell of reactive bone surrounding a medullary lesion, classically seen in monostotic fibrous dysplasia of the proximal femur.
Key imaging points
- Modality: best appreciated on plain radiograph, also visible on CT as dense cortical-like rim.
- Appearance:
- Well-defined intramedullary lucent / ground-glass lesion.
- Markedly thick sclerotic border (“rind”) – much thicker than the usual thin benign sclerotic margin.
- Often metaphyseal/diaphyseal in long bones, especially proximal femur.
- Associated changes (if fibrous dysplasia):
- Mild expansion, cortical thinning.
- Possible deformity (e.g. shepherd’s crook).
Typical association
- Exam-safe association:
- Rind sign + proximal femur + young patient → Fibrous dysplasia.
Differentials (rind-like lesions)
- Liposclerosing myxofibrous tumour – adult, intertrochanteric femur, mixed lytic–sclerotic, irregular thick rim.
- Healed/simple bone cyst or other fibro-osseous lesion – can have a prominent rim but usually less “classic”.
- Bone infarct – tends to have serpiginous central sclerosis, not a smooth, circumferential rind.
