Non-ossifying fibroma (NOF)

Case contributed by Dr Mohammad A. ElBeialy

Presentation

8 years old boy with history of recent trauma to the right shoulder and right upper arm pain.

Patient Data

Age: 8 years
Gender: Male
Modality: X-ray

Plain radiographs show upper lateral humeral well-demarcated eccentrically located lobulated cortical based lesion with medullary encroachment. The lesion has thin sclerotic margin. The lesion is oriented parallel to the long axis of the bone. No matrix calcification. Associated cortical expansion with no definite cortical breakthrough. No periosteal reaction.   

Modality: MRI
  • the antero-lateral aspect of proximal humeral metadiaphysis shows a well-defined lobulated fairly fusiform predominantly cortical expansile lytic mass lesion, with sclerotic margin and narrow zone of transition. The lesion causes medullary encroachment.
  • the lesion shows heterogenous predominantly hypointense T1 and intermediate T2 signal with foci of hypo- and hyperintensities. No evident fluid / fluid levels seen. No evident pathological fracture.
  • the lesion measures about 5 X 1.8 X 1.8 cm in its maximal craniocaudal and axial cross-sectional dimensions, respectively. No definite cortical destruction or pathological fracture.
  • the lesion is seen indenting the undersurface of the deltoid muscle with thin rim of fluid signal intervening.

Case Discussion

A well-demarcated expansile eccentric lytic lesion with scalloped sclerotic margins parallel to the long axis of the metaphyses of long bones is virtually diagnostic of non-ossified fibroma.

Non-ossifying fibroma is also known as fibroxanthoma. Fibrous cortical defect (FCD) is a fibroxantoma smaller than 2 cm. NOF is a "DO NOT TOUCH" lesion. No further work-up is required.

The DDx of NOF is:

  • simple bone cyst (SBC): central lytic lesion with fallen fragment sign in case of pathological fractures.
  • aneurysmal bone cyst (ABC): eccentrically located lesion with marked bone expansion and periosteal reaction. Fluid/ fluid level is diagnostic.
  • fibrous dysplasia: expansile medullary lesion with ground glass attenuation. Fibrous dysplasia is a long disease in a long bone!  
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Case Information

rID: 25846
Case created: 12th Nov 2013
Last edited: 25th Feb 2017
Inclusion in quiz mode: Included

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