Fibrous Dysplasia Overview

Fibrous Dysplasia

• Benign condition affecting bones, often in childhood/adolescence, rarely after 30.
• Caused by abnormal osteoblasts, replacing healthy bone with fibrous tissue.
• Most cases are monostotic (affecting one bone), but about 20% are polyostotic (affecting multiple bones).
• Long bones are more commonly affected in polyostotic cases, but virtually any bone can be involved.
• Diagnosis is often by X-ray or CT, showing "ground glass" appearance in the medullary (center) of the bone, commonly causing bony expansion.
• Increased risk of fractures, but without acute injury, there's usually no periosteal reaction.
• Bone scan shows increased uptake, not helpful in diagnosis.
• Secondary degeneration can lead to osteosarcoma, particularly in those exposed to radiation, signaled by pain and soft tissue mass growth.

Eponymous/Descriptive Terms Related to Fibrous Dysplasia

• Shepherd's Crook Deformity: Coxa varus deformity of the proximal femur, caused by chronic bowing and remodeling secondary to microfractures in the bone. Similar appearances are possible in Paget disease and osteogenesis imperfecta.
• Protrusio Acetabuli: Fibrous dysplasia can cause femoral head protrusion into the pelvis due to acetabulum remodeling.
• Leontiasis Ossea: Facial involvement, resembling a lion, due to canal stenosis (narrowing) by bony expansion. Can cause cranial nerve palsies.
• Cherubism: Maxilla and mandible facial involvement resulting in a cherubic appearance. Also causes canal stenosis and potential cranial nerve palsies. Inherited in an autosomal dominant pattern.

McCune-Albright Syndrome

• Primarily affects females.
• Triad of symptoms:
  • Cafe-au-lait spots (often on the back and respecting the midline).
  • Precocious puberty (or other endocrine issues).
  • Polyostotic fibrous dysplasia.

Mazabraud Syndrome

• Very rare.
• Polyostotic fibrous dysplasia, along with soft tissue tumors.
• Increased risk of malignant degeneration to osteosarcoma.