Conventional radiography is probably the most helpful assessment in order to make diagnosis; typically,
non-ossifying fibroma is a well defined,
osteolitic,
eccentric subcortical lesion,
often lobulated,
with a sclerotic rim (Fig.1).
It is usually located at the metaphysis of long bones of femur and tibia,
near conjugation cartilage,
but atypical presentations can be seen (such as fibula,
homer,
clavicle) (Fig.2),
especially in cases of multiple non-ossifying fibromas associated to specific syndromes like neurofibromatosis type 1 and Jaffe-Campanacci syndrome3.
Non-ossifying fibroma does not cause involvement of the surrounding soft tissues and has no periosteal reaction,
unless a fracture is associated.
Computed tomography (CT) and magnetic resonance imaging (MRI) are useful only in selected cases,
for example when diagnosis is uncertain; CT is generally used to better evaluate the cortical bone and the risk of fracture (Fig.
3),
while MRI is able to exclude the involvement of the surrounding soft tissues with better accuracy.
MR imaging depends on when the exam is performed in the development or healing phase of the lesion4.
Initially,
the lesion has an intermediate to high signal intensity in the T2-weighted sequences and intermediate to low in the T1-weighted sequences,
with a low peripheral signal corresponding to the sclerotic rim (Fig.
4).
As the bone grows and the lesion is filled by the normal bone from the periphery,
signal becomes low in all sequences5.
Even after contrast injection,
the enhancement is variable6 (Fig.5).
Main differential diagnoses include:
- cortical fibrous defect,
which differs for a dimensional standard (<2 cm,
while non-ossifying fibroma is >2 cm),
- aneurysmal bone cyst,
that can be anywhere in the skeleton and is filled with blood,
- condromixoid fibroma,
very rare,
with a sclerotic inner margin and cortical destruction on the outer side,
- fibrous dysplasia,
which is a benign lytic lesion with fibro-osseous tissue proliferation; it often presents a ground-glass appearance with matrix calcifications,
- eosinophilic granuloma,
or Langerhans cell histiocytosis,
which can be a sclerotic or osteolytic lesion,
with either well or ill defined margins; it often involves the skull.
Non-ossifying fibroma is considered a "don’t touch lesion",
since most of them don’t require any treatment or biopsies.
Prophylactic curettage and bone grafting are only indicated in case of large lesionfibro-osseus tissuefibro-osseus tissues,
with risk of pathmargins ological fractures6.
It has been demonstrated how NOF’s fractures may heal even without bone grafting7-8,
even if bone grafts accelerate the process9.