Fibrous dysplasia is a developmental abnormality characterized by a disorganized mixture of fibrous and osseous elements in the medullary region of affected bones.
Fibrous dysplasia of bone is a disease of unknown cause which involves either a single bone (monostotic form) or several bones (polystotic form). Both forms occur in the temporal bone.
Monostotic Fibrous Dysplasia
Monostotic fibrous dysplasia is the most common form of the disease and is most often seen in the second and third decade, with no predilection for either sex. The bones commonly involved are femur, tibia, ribs and facial bones, although any bone may be affected. The disease may have no clinical signs or it may lead to a fracture.
Polystotic Fibrous Dysplasia
One fourth of patients with polystotic fibrous dysplasia exhibit disease in more than half of the skeleton, including the facial bones. Symptoms usually seen in childhood, and almost all patients have pathological fractures, or limb deformities. Polystotic fibrous dysplasia is more common in females. Pregnancy may stimulate the growth of lesions.2 Although monostotic cases in the femur can predispose to fracture, the majority of monostotic cases at other sites do not progress and the long-term outcome is favorable regardless of treatment.3
Pathologically, the disease is characterized by abnormal proliferation of fibrous tissue within cancellous (spongy) bone. This fibro-occeous tissue replaces normal bone and fills all the pneumatic air cells. The disease occurs in children and adults.
Fibrous Dysplasia of Bone and Paget's Disease
Fibrous dysplasia of the temporal bone is very rare. It is frequently located in the midface in frontal skull base. The affected areas are thickened. Similar tumor-like changes can be caused by Paget's disease.
Sarcomas in Fibrous Dysplasia
Malignancy is a well-known complication in patients with fibrous dysplasia. Although a complication in both monostotic and polystotic disease, it is more common in polystotic type. The most frequent tumor is osteogenic sarcoma, although fibrosarcoma, chondrosarcoma, and malignant fibrous histiocytoma have been described. The bones involved are the skull, facial bones, and femur. Radiation, not the preferred treatment for fibrous dysplasia, significantly increases the risk of malignant transformations.3
Prognosis for Fibrous Dysplasia of Bone
The prognosis is usually good but it depends on the form and the extent of the disease and the location of the lesions. The monostotic form stops growing at puberty, and there is some evidence of the decrease of the activity of polystotic form at this age as well.1
Fibrous Dysplasia in Animals
Although quite rare, fibrous dysplasia occurs in horses, dogs, and cats. Familial canine polystotic fibrous dysplasia has been seen in doberman pinscher puppies and Old English Sheepdogs. As in humans, young animals are most often affected by fibrous dysplasia.4 The condition is characterized by swelling just above the wrist of the forelegs. This is accompanied, or followed, by lameness at about 5-7 months of age. The bone material is replaced by fibrous tissue which contains pockets of degenerative matter and straw-colored fluid. The disease may be successfully treated by surgery. A genetic basis is suspected.5
- Manual of middle ear surgery, Volume 3. Mirko Tos
- Rubin's Pathology: clinicopathologic foundations of medicine. Raphael Rubin, David S. Strayer
- Orthopaedic Pathology. Vincent J. Vigorita, Bernard Ghelman, Douglas Mintz
- Tumors in domestic animals. Donald J. Meuten
- Genetics for dog breeders. Roy Robinson