Presentation
Hip pain. No reported trauma.
Patient Data
The proximal right femur shows a diffusely abnormal irregular trabecular pattern with areas of increased and decreased osseous density and ground-glass opacity. This lesion causes moderate cortical thinning with endosteal irregularity. There is no associated periosteal reaction or definitive soft-tissue mass. The proximal epiphysis of the right femur is spared. Similar lesions are present within the right ilium in the supra-acetabular region and along the iliac crest. The right femoral neck demonstrates a focally expansile lytic lesion with severe cortical thinning which appears to be a distinct lesion from the changes described previously. The cortex along the inferior margin of the right femur is not definitively intact, and may represent an area of cortical disruption indicating a pathological fracture.
The distal femur and tibia are grossly abnormal showing diffuse areas of ground-glass opacity within areas of soap-bubbly trabeculation which cause endosteal irregularity, cortical thinning and moderate osseous expansion. The epiphyses are spared, and no periosteal reaction or associated soft-tissue mass are present.
There is diffuse intraosseous abnormality characterized by heterogeneously increased STIR signal which is intermediate to low on T1 involving the right iliac bone, anterior acetabulum, femoral head, neck, metaphyses and diaphysis. The cortex is thinned throughout most of the femur to a varying degree, with several regions of severe cortical thinning.
A large area of cystic degeneration with fluid-fluid levels is present within the right femoral neck. The cortex is severely thinned surrounding this area, however no displaced fracture is noted at this site. There is a small right hip effusion with no adjacent soft tissue edema.
At least 3 discrete intramuscular masses with low T1 and high STIR signal are present, which demonstrate heterogeneous enhancement following contrast administration. The largest of these lies within the vastus intermedius.
Case Discussion
The bony changes seen in this case are typical for polyostotic fibrous dysplasia with an associated secondary aneurysmal bone cyst in the right femoral neck; however, the presence of intramuscular myxomatous lesions indicate that this is not simply polyostotic fibrous dysplasia but rather Mazabraud syndrome. Fibrous dysplasia may be either monostotic or polyostotic in Mazabraud syndrome, but is typically polyostotic.
The intramuscular myxomas in this case were biopsy proven, however biopsy is not critical because the lesions are characteristic in this setting and there is no potential for malignant degeneration.
Less than 100 cases of Mazabraud syndrome have been reported.
This case was shared with me by the late and great Dr. Deborah Forrester.
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