Definition
- Rare benign, locally aggressive bone tumour
- Bland spindle cells in abundant collagen
- Intraosseous counterpart of desmoid fibromatosis
- Does not metastasise
Epidemiology
- Among the rarest primary bone tumours
- Adolescents and young adults, usually under 30
- No clear sex predilection
- Mandible most frequent, then femur, humerus, tibia, radius and pelvis
Pathology
- Low cellularity spindle and stellate cells with minimal atypia
- Dense collagen resembling desmoid, with rare mitoses
- Infiltrates between existing trabeculae
- CTNNB1 mutation and nuclear beta-catenin in some cases
Clinical Features
- Mild pain, swelling or palpable mass
- Pathological fracture in a minority
- Some lesions are incidental
Investigations
- Purely lytic, expansile metaphyseal lesion extending into the diaphysis
- Well defined margins with pseudotrabeculation giving a “soap bubble” appearance
- No mineralised matrix
- Aggressive lesions breach cortex with soft tissue extension
- Low T2 signal areas on MRI reflect collagen content
- Biopsy correlated with imaging
Differential Diagnosis
- Low grade fibrosarcoma
- Low grade central osteosarcoma, separated by MDM2 amplification
- Fibrous dysplasia and non-ossifying fibroma
- Aneurysmal bone cyst and giant cell tumour of bone
- Chondromyxoid fibroma
Management
- Wide or marginal en bloc resection gives the lowest recurrence
- Curettage with burr, phenol or cryotherapy where resection would be morbid
- Reconstruction with allograft, autograft or endoprosthesis
- Radiotherapy has little role
- Long term clinical and radiological follow up
Prognosis
- Recurrence common after intralesional treatment, less after resection
- No malignant transformation or metastasis
- Malignant behaviour prompts review for fibrosarcoma or osteosarcoma
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.