Fibrous bone dysplasia of the third distal femur in children

Clinical History

A 13 years old children came to our hospital with pain at the level of the right distal leg with a suspected femoral fracture. The patient underwent X-ray examination that showed an ostheolitic lesion of 11 cm in diameter with a pathologic fracture. Consecutively the patient underwent an MRI examination.

Imaging Findings

A 13 years old children came to our hospital with pain at the level of the right distal leg with a suspected femoral fracture. The patient underwent X-ray examination that showed an ostheolitic lesion of 11 cm in diameter with a pathologic fracture ( Fig 1a,1b ). Consecutively the patient underwent an MRI examination; T1 with and without fat suppression and T2 weighted sequences were performed in the axial ( Fig 2 ), sagittal and coronal planes, before and after the injection of gadolinium ( Fig 3 ). MRI confirmed a solid mass on the posterior-medial level of the third distal femur with a diameter of 11 cm. The cortical was thickened with peripheral sclerosis and normal periosthium. MRI confirmed a spiroid fracture and showed oedema at the level of soft tissue ( Fig 4). MRI was suggestive for fibrous bone dysplasia; patient underwent an orthopaedic examination and a biopsy confirmed the diagnosis.

Discussion

Fibrous dysplasia is a rare condition in which bone tissue is replaced by fibro-osseous lesions (1). This disease can involve one or several bones and is characterized by bone deformities, pain and iterative fractures. Some patients can present with endocrine dysfunction, generally precocious puberty. Some complications, such as nerve compression and malignant transformation, are uncommon. Many patients can, however, be asymptomatic. Diagnosis relies on X-ray examination MRI and pathology. Prognosis is assessed by X-rays and markers of bone remodelling. It is now recognized that fibrous dysplasia is caused by a somatic activating mutation of the Gs alpha subunit of protein G, resulting in an increased cAMP concentration and thus in abnormalities of osteoblast differentiation, these osteoblasts producing abnormal bone. There is also an increase in interleukin-6-induced osteoclastic bone resorption, which is the rationale for treating these patients with bisphosphonates(2). A safe differentiation of fibrodysplastic lesions from "real" bone tumours is of high importance because a fibrous dysplasia often requires no further therapy (3). Magnetic resonance imaging is considered the modality of choice for evaluation of other benign musculoskeletal lesions because it is highly sensitive to changes in the signal intensity of bone marrow and adjacent soft tissues. It provides useful information for diagnosis of the lesion as in primary or secondary aneurysmal bone cyst, chondroblastoma, osteoblastoma, fibrous dysplasia, and osteofibrous dysplasia, and it helps differentiate these lesions from osteomyelitis, Langerhans' cell histiocytosis, and stress fracture(4). Intramedullary fixation should be the first choice to treat femoral fractures and to prevent refractures in patients with fibrous dysplasia (1).

Differential Diagnosis List

Final Diagnosis

The histological specimen revealed a fibrous bone dysplasia

URL:	https://www.eurorad.org/case/3419
DOI:	10.1594/EURORAD/CASE.3419
ISSN:	1563-4086