Radiology Corner – Monostotic Fibrous Dysplasia

 

By: Terry R. Yochum, DC, DACBR, Fellow, ACCR, and Chad J. Maola, DC

Figure 1. Any fracture here?

Figure 1. Any fracture here?

Case History

This young adult presents with pain in the hip after suffering trauma. Is there a fracture?

DIAGNOSIS

Monostotic Fibrous Dysplasia. Observe the geographic radiolucency just below the lesser trochanter. There is a “ground glass” matrix and a sclerotic border. There is no fracture.

DISCUSSION 

The skeletal lesions of fibrous dysplasia are not usually present at birth; they are present, however, several years prior to puberty and often progress throughout the entire life of the patient. Because of the progressive turnover of bone, patients with fibrous dysplasia will have a positive bone scan.All of the bones of the body may be involved; however, there is a particular site predilection for monostotic and polyostotic involvement.

Monostotic Fibrous Dysplasia. The most common location for monostotic fibrous dysplasia is in the proximal one-third of the femur and the ribs.Most lesions affecting the long bones are placed in the diametaphysis and spare the subarticular surface of the bone. This anatomic predilection is helpful in the differential diagnosis of Paget’s disease. Paget’s disease on occasion may mimic fibrous dysplasia; however, involvement of the tubular bones in Paget’s disease invariably extends to include subarticular bone.

Figure 2. What about here?

Figure 2. What about here?

The lesions of monostotic fibrous dysplasia are usually radiolucent, often having a loculated or trabeculated appearance. Scattered throughout the fibrous lesion, there is an appearance of radiopacity. This represents the classic “ground glass” or “smoky” appearance of bone. This represents a base matrix of fibrous tissue with scattered osteoid, which Jacobson so appropriately calls the “wipe out of the trabecular patterns appearance.3

Many students of radiology have struggled with the phrase, “ground glass appearance of bone.” After hearing numerous explanations, the most plausible one offered suggests the appearance of glass following a grinder being used on its external surface to disturb its glistening sheen. This renders a homogenous, ill-defined density across the surface of the glass, which is very characteristic of the appearance within the medullary canal of the bones involved in fibrous dysplasia.4

These geographic cystic lesions are often very well demarcated and in the monostotic form, usually have a very thick, sclerotic border, referred to by Jacobson as the “rind” of sclerosis.3 There is a widening of the medullary canal, and the endosteum is often thinned and scalloped. Expansion of bone is a common finding. Deformity of bone, particularly in weightbearing bones, is often found and occasionally is associated with pathologic fracture. There is no evidence of periosteal response, except in those cases following pathologic fracture or malignant change. Most of these lesions render a very typical and characteristic appearance, allowing the radiologist to establish the correct diagnosis in a high percentage of cases (Fig. 3).

 

Figure 3. Note the large geographic “soap-bubbled” lytic lesion in the proximal femur characteristic of fibrous dysplasia. These lesions are often hot on bone scan.

Figure 3. Note the large geographic “soap-bubbled” lytic lesion in the proximal femur characteristic of fibrous dysplasia. These lesions are often hot on bone scan.

References

1. Edeiken J. Roentgen Diagnosis of Diseases of Bone, 3rd ed. Baltimore: Williams & Wilkins, 1981.

2. Gibson MJ, Middlemiss JH. Fibrous dysplasia of bone. Br J Radiol 1971; 44:1.

3. Murray RO, Jacobson HG. The Radiology of Skeletal Disorders, 2nd ed. London: Churchill Livingstone, 1977.

4. Yochum TR, Rowe LJ. Essentials of Skeletal Radiology, 3rd ed. Baltimore: Williams & Wilkins, 2004:1190.