Ossifying fibroma

Ossifying fibromas (OF), also commonly referred to as osteofibrous dysplasia (OFD), especially when in the extremities, are benign bone lesions that should be differentiated from non-ossifying fibromas and fibrous dysplasia.

Epidemiology

These lesions are most frequently encountered in young children (often <10 years).

Pathology

Histology

They comprise of haphazardly distributed lamellated bony spicules on a background of fibrous stroma. Despite being benign, they can be locally aggressive. Immunohistochemical staining of lesions shows positive keratin cells in the majority of the cases.

Location

• lower extremity
  • tibia: most frequent site ⁵ (90% of the time); there is a predilection for the anterior tibial cortex
  • femur: occurs in a diaphysial location
• mandible and maxilla: these are examples of cementum-poor cement-ossifying fibromas ² (see WHO classification scheme for odontogenic tumours)
• sinonasal: expansile lesions with peripheral ossification and central lucency

Radiographic features

Plain radiograph and CT

• well-circumscribed lesion
• evidence of intracortical osteolysis with a characteristic sclerotic band (osteoblastic rimming)
• moderate cortical expansion
• homogeneous lesion matrix

MRI

Reported signal characteristics include

• T1: low signal
• T2: iso-high signal
• T1 C+ (Gd): typically shows enhancement

Treatment and prognosis

Tend to regress over time. For locally aggressive lesions, surgical resection is often curative although recurrence has been reported.

Complications

• pathological fracture(s)
• limb bowing

Differential diagnosis

Imaging differential considerations include

• fibrous dysplasia: has no osteoblastic rimming
• adamantinoma: may share a common origin with ossifying fibromas
• osteoid osteoma

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