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

Radiograph and CT
  • seen as a well-circumscribed lesion
  • demonstrates 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

Differential diagnosis

Imaging differential considerations include


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Bone tumours

The differential diagnosis for bone tumours is dependent on the age of the patient, with a very different set of differentials for the paediatric patient.

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