Non-ossifying fibroma - an atypical presentation and bone scan appearance

Background: Non-ossifying fibroma (NOF) is a benign lesion that occurs commonly in the diametaphysis of the long bones in the lower extremities. It is often asymptomatic and found incidentally during routine radiographic evaluation. It is considered a developmental defect with characteristic radiological stages of progression, migration and regression ‘healing.’NOF shows variable degrees of uptake on bone scan, usually minimally to mildly increased during the progression and migration phase and mild hyperaemia and moderate uptake during the regression ‘healing’ phase.
Case Review and Results: An otherwise well 25-year-old female presented with atraumatic right distal thigh pain for 3 weeks. Her three-phase bone scan with SPECT-CT demonstrated intense focal hyperaemia in a ring like pattern on early images and markedly increased uptake on delayed images in the right distal diametaphysis of femur (most intense in the lateral cortical aspect) localising to an eccentric osteolytic lesion with an sclerotic margin on the low dose CT. There was no cortical erosion or fracture line with the lesion was noted to involve greater than 50% of the femoral diameter. The bone scan findings favoured the diagnosis of NOF complicated by micro fractures. Subsequently, a biopsy of the lesion confirmed the diagnosis of non-ossifying fibroma.
Conclusion: Bone scan was helpful in investigating this patient’s lower limb pain. The biopsy was helpful to confirm the diagnosis, reassure the patient and exclude other pathologies such as fibrous dysplasia, giant cell tumour or aneurysmal bone cyst.