Craniofacial fibrous dysplasia
Craniofacial fibrous dysplasia is one of four types of fibrous dysplasia and is characterised, as the name suggests, by involvement of the skull and facial bones.
For a general discussion of the underlying pathology, refer to the parent article fibrous dysplasia.
Although the term leontiasis ossea has been used synonymously with craniofacial fibrous dysplasia, its use is discouraged, as the former has been used to describe a number of entities.
Young adult patients are most frequently affected. Refer to fibrous dysplasia article for a discussion of epidemiology.
Craniofacial involvement may occur both as true craniofacial fibrous dysplasia, considered a form of monostotic fibrous dysplasia (despite multiple cranial bones being affected) which accounts for 10-25% of monostotic cases, or as part of polyostotic fibrous dysplasia.The craniofacial bones are affected in up to 50% of polyostotic cases 1. Occasionally it is seen in the setting of McCune-Albright syndrome 2.
Presentation is usually cosmetic or due to mass effect on cranial structures:
- cranial asymmetry
- facial deformity
- nasal stuffiness
- visual impairment/unilateral blindness
Refer to fibrous dysplasia article for a discussion of pathology.
The anterior craniofacial bones are more frequently involved than more lateral or posterior portions; sphenoid, frontal, maxillary, ethmoid bones > occipital, temporal bones. Extracranial involvement is rare 6.
Similar to fibrous dysplasia elsewhere, affected bones demonstrate a variety of radiographic features ranging from lucency to sclerosis.
- blistering/bubbling cystic skull vault lesions
- commonly cross sutures
- sclerotic skull base
- widened diploic space with displacement of outer table; inner table spared (this is in contrast to Paget disease, in which case the inner table is involved)
- obliteration of paranasal sinuses
Affected bones are usually expanded with an intact cortex and lose the normal corticomedullary differentiation, being replaced classically by a homogeneous ground glass appearance, although mixed lucencies and sclerosis are also common 2-4.
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 may be present 2. Sometimes the mixed regions of sclerosis and lucency are reminiscent of Paget disease, and are thus referred to as 'pagetoid' 3.
When the maxilla or mandible are involved, resorption of the roots of teeth is uncommon 2.
MRI appearance is variable depending on the degree of lucencies versus sclerosis 2-4.
- T1: heterogeneous signal, usually intermediate
- T2: heterogeneous signal, usually low, but may have regions of higher signal
- T1 C+ (Gd): heterogeneous contrast enhancement
Treatment and prognosis
Treatment is reserved for cases where function is being threatened (particularly the airway or vision) and is surgical, although much controversy exists over the best approach (e.g. early vs late intervention, minimal vs radical resection).
As the region affected is often large and involves complex facial anatomy, complete resection is usually not possible. Likewise, reconstruction can be challenging 5.
Historically, radiotherapy was used to attempt to control growth. This not only was of limited success but encouraged sarcomatous degeneration, and is thus now contraindicated 5.
General imaging differential considerations include:
- histology may be similar; however, trabeculae are rimmed by osteoblasts
- usually more sharply defined
- may appear very similar
- usually abuts intracranial compartment
- predilection for skull vault
- usually spares facial skeleton
- usually little expansion
- usually has different demographics
- 1. Chong VF, Khoo JB, Fan YF. Fibrous dysplasia involving the base of the skull. AJR Am J Roentgenol. 2002;178 (3): 717-20. AJR Am J Roentgenol (full text) - Pubmed citation
- 2. Larheim TA, Westesson P. Maxillofacial Imaging. Springer Verlag. (2008) ISBN:3540786856. Read it at Google Books - Find it at Amazon
- 3. Som PM, Curtin HD. Head and Neck Imaging, Volume 1 und. Mosby. (2003) ISBN:0323009425. Read it at Google Books - Find it at Amazon
- 4. Fitzpatrick KA, Taljanovic MS, Speer DP et-al. Imaging findings of fibrous dysplasia with histopathologic and intraoperative correlation. AJR Am J Roentgenol. 2004;182 (6): 1389-98. AJR Am J Roentgenol (full text) - Pubmed citation
- 5. Thaller S, Garri JI, Bradley JP. Craniofacial Surgery. Informa HealthCare. (2007) ISBN:0849382106. Read it at Google Books - Find it at Amazon
- 6. Chapman & Nakielny's Aids to Radiological Differential Diagnosis: Expert Consult - Online and Print, 6e. Saunders Ltd. ISBN:0702051764. Read it at Google Books - Find it at Amazon