MyPACS.net: Radiology Teaching Files > Case 53507469

Never visited CRANIOFACIAL FIBROUS DYSPLASIA
Contributed by: antonio aguiar, Radiologist, Real Hospital PortuguÍs De Pernambuco - Realimagem, Brazil.
History:

Patient 01: 46 – year – old woman, with right proptosis.

Patient 02: 29 – year – old woman.

Patient 03: 07 – year – old boy.

This case has no images yet.
Findings:

Figure 01 (patient 01): skull x ray - Sclerosis and thickening of the right sphenoid bone (arrow).

Figure 02 (patient 02): axial computed tomography (CT), wide window – the right parietal bone is expanded, with heterogeneous ground glass appearance and intact cortex (arrow).

Figure 03 (patient 02): axial CT, wide window – thickening of the right parietal bone, with heterogeneous ground glass appearance and cystic component (arrow).

Figure 04 (patient 03): axial CT, wide window – there is thickening and a ground glass appearance of the right temporal bone, the sphenoid bone and both lateral orbit wall (arrows).

Figure 05 (patient 03): axial CT – the affected bones (right temporal, ethmoid and both lateral orbit wall) has a ground glass appearance  (arrows).

Diagnosis: Craniofacial fibrous dysplasia.
Discussion:

Fibrous dysplasia (FD), is a skeletal developmental anomaly of the bone-forming mesenchyme resulting from abnormal osteoblast function. Fibrous dysplasia is a nonheritable disease related to a sporadic mutation in the gene that encodes the subunit of a stimulatory G protein on chromosome 20. As a result, osteoblasts abnormally produce fibrous tissue within the bone marrow.

Macroscopically the medullary cavity is filled by abnormal whitish fibrous tissue. On histology, the fibrocellular matrix of immature collagen contains small irregularly shaped trabeculae of immature, inadequately mineralized bone trabeculae not rimmed by osteoblasts. cartilaginous islands present in 10%.

Fibrous dysplasia represents approximately 5% of all benign bone tumors. Any bone can be affected. Fibrous dysplasia can be divided into four sub types, although there is some overlap:

   - Monostotic : involving only one bone. This is by far the most common and accounts for 70 - 80% of cases. It is usually asymptomatic until 2nd - 3rd decade, but can be seen throughout adulthood. After puberty the disease becomes inactive, and monostotic form does not progress to polyostotic form. In monostotic form craniofacial bones are involved in 10 - 25%.

   - Polyostotic : In the remaining 20 - 30% of cases multiple bones are involved. As expected this presents earlier, typically in childhood, mean age of 8 years, with 2/3rds having become symptomatic by the age 10. In polyostotic cases there is a tendency for the lesions to be unilateral. If the lesions are bilateral, they are not symmetrical. In polyostotic form skull and facial bones are affected in 50 %.   

   - Craniofacial fibrous dysplasia : this is characterised by involvement of the skull and facial bones.

   - Cherubism : mandible and maxilla alone (not true fibrous dysplasia).

Fibrous dysplasia usually presents in persons aged 3-15. Most cases (75%) manifest themselves before the age of 30. There is no recognised gender predilection. Fibrous dysplasia may be associated with McCune-Albright syndrome, which occurs almost exclusively in females. The combination of bone lesions with areas of skin pigmentation and precocious puberty comprises the Albright syndrome. Without sexual precocity, the entity has been termed Jaffe-Lichtenstein disease.

Craniofacial fibrous dysplasia is characterized by involvement of the skull and facial bones. The craniofacial bones are affected in 10 - 25% of monostotic cases and up to 50% of polyostotic cases. The skull is relatively common affected. The pattern is generally mixed. The most commonly affected parts are the calvarium and floor of the anterior fossa. The vague term leontiasis ossea has been applied to a sclerosing form affecting one side of the face and, perhaps, the skull base. The mandible may also be affected by either cystic or sclerotic lesions.

The condition is often an incidental finding and is usually painless. Attention may first be drawn to the condition by cosmetic, like cranial asymmetry or facial deformity. It may present due to bony expansion. Morbidity may arises from compression and displacement of adjacent structures. The content of the orbit or cranial nerves may be compressed, with proptosis or visual impairment and unilateral blindness. No characteristic biochemical changes are found.

Sarcomatous de-differentiation (osteosarcoma, fibrosarcoma, malignant fibrous histiocytoma or rarely chondrosarcoma) is seen in less than 1% of cases of fibrous dysplasia, and is more common in the polyostotic form.

Characteristic radiographic findings include a relatively homogenous lucent lesion with or without bone expansion commonly described as a ground-glass appearance, with displacement of outer table and inner table spared; the lesions usually cross sutures; additionally the lucent lesion has a thick sclerotic border that is called the rind sign. There should be an absence of periosteal reaction. Occasionally, there is  bubbly cystic lesions. Flecks of calcium are sometimes seen within the translucent zones. It is important to remember that unaffected bone is of normal density. Obliteration of  paranasal sinuses may occur.

Computed tomography (CT) is very useful in evaluating the extent of disease in complex areas, as the craniofacial bones. The affected bones are usually expanded with an intact cortex and lose the normal cortico-medullary differentiation, being replaced classically by a homogeneous ground glass appearance, although mixed sclerosis and lucencies are also common. The margin between abnormal and normal bone is often difficult to identify, the two regions blending with each other, however on occasion a relatively sharp demarcation with well-defined borders may be seen. Cystic components may be present in the early active stage. 

Magnetic resonance (MR) is not particularly useful in differentiating fibrous dysplasia from other entities as there is marked variability in the appearance of the bone lesions, and they can often resemble tumour or more aggressive lesions. MR appearance is variable depending of the degree of lucencies versus sclerosis. The expanded, thickened bone is typically low to intermediate on both T1 and T2 weighted MR scans, although scattered hyperintense regions may be present. The lesion has heterogeneous contrast enhancement.

Nuclear imaging may also be used in conjunction with other imaging modalities to assist with the diagnosis of fibrous dysplasia. Nuclear imaging demonstrates increased tracer uptake on Tc99 bone scans, However, it is not specific for fibrous dysplasia. Lesions remain metabolically active into adulthood.

Needle biopsy can be used to confirm the diagnosis if there is uncertainty.

Asymptomatic patients do not require treatment. Bisphosphonates have been shown to be helpful treating chronic bone pain associated with fibrous dysplasia. Usually no treatment is required as the bone lesions usually do not progress beyond puberty. Treatment is reserved for cases where function is being threatened, particularly the airway or vision, then surgical decompression may be considered. Surgery may also be utilized for the treatment of severe deformity.

References:

1. Sutton D. A textbook of Radiology and Imaging. 3rd ed. Churchill Livingstone. Edinburgh, EH1. 1980.

2. Putman CE; Ravin CE. Textbook of Diagnostic Imaging. 1st ed. W.B.Saunders Company. Philadelhia, PA. 1988.

3. Yock DH. Imaging of CNS Disease – A CT and MR Teaching File. 2nd ed. Mosby - Year Book, Inc. St Louis, MO. 1991.

4. Latchaw RE. MR and CT Imaging of the Head, Neck, and Spine. 2nd ed. Mosby - Year Book, Inc. St Louis, MO. 1991.

5. Osborn AG. Diagnostic Neuroradiology. 1st ed. Mosby – Year Book, Inc. St. Louis, MO. 1994.

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Additional Details:

Case Number: 53507469Last Updated: 2011-07-18
Anatomy: Cranium and Contents   Pathology: Neoplasm
Modality: CT, Conventional RadiographAccess Level: Readable by all users
Keywords: fibrous dysplasiaACR: 10.355

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