Polyostotic Lytic Lesions

Fibrous Dysplasia

Polyostotic Fibrous dysplasia is a bone condition that frequently affects a limb or one side of the body, but can affect any combination of multiple bones in the body.  Patient often will have involvement of the entire bone.  Fibrous dysplasia on plain radiograph is often described as a long lesion in a long bone with a ground glass appearance to it.  A more modern way to perceive a ground glass lesion is if you imagine looking through a glass shower door.  Fibrous dysplasia is usually well circumscribed and may show cortical thinning at the site of the lesion.  It is usually hot on bone scan.  It is usually not associated with a soft tissue mass but if it is, one should be concerned for some other associated or similar appearing process like ostegenic sarcoma.  In the proximal femur, the classic shepards crook deformity will often be evident.  In this deformity, the proximal femoral neck takes on a varus deformity with an overgrowth of the greater trochanter.  Given the appearance of a shepard's crook.

Polyostotic fibrous dysplasia is frequently associated with the condition McCune-Albright's syndrome.  These patients present with coast of california shaped caffe au lait skin lesions, polyostotic fibrous dysplasia, short stature and endocrine abnormalities.  The endocrine abnormalities most often present as precocious puberty, but can present as any number of hormonal disturbances.  McCune-Albright Syndrome, as with fibrous dysplasia is associated with a mutation in the alpha subunit of a stimulating G-protien, which regulates intracellular cyclic AMP.  The mutation in the G-protien results in constitutive activation of the g-protien cascade resulting in elevated levels of intracellular cAMP.

Patients with fibrous dysplasia are at increased risk of fracture in the involved bones.  The bones may also undergo microfracture, leading to slowly progressive deformity, like that seen in the proximal femur.  Bones at risk of fracture should undergo prophylactic stabilization to prevent fracture when ever possible.  If bone graft is used in the lesion, cortical allograft should be used, not cancellous bone.  Cancellous bone is often re-absorbed by the lesion and truned back into a fibrous dysplasia lesion.

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