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Craniofacial fibrous dysplasia

Craniofacial fibrous dysplasia is one of 4 types of fibrous dysplasia and is characterised (as the name suggests) by involvement of the skull and facial bones. Although leontiasis ossea has been used synonymously with craniofacial fibrous dysplasia, as the former has been used to describe a number of entities, its use is discouraged.

For a general discussion of the underlying pathology, refer to the parent article fibrous dysplasia.

Epidemiology

Young adult patients are most frequently affected. Refer to fibrous dysplasia article for a discussion of epidemiology.

Clinical presentation

Craniofacial involvement may occur both as true craniofacial fibrous dysplasia, considered a form of monoostotic fibrous dysplasia (despite multiple cranial bones being affected) which accounting for 10-25% of monoostotic 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
  • proptosis
  • visual impairment / unilateral blindness

The anterior craniofacial bones are more frequently involved than more lateral or posterior portions; sphenoid, frontal, maxillary, ethmoid bones > occipital, temporal bones. 

Pathology

Refer to fibrous dysplasia article for a discussion of pathology.

Radiographic features

Similar to fibrous dysplasia elsewhere, affected bones demonstrate a variety of radiographic features ranging from lucency to sclerosis.

Plain film
  • 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
CT

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 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 there the mixed regions of sclerosis and lucency are reminiscent of Paget's 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

MRI appearance is variable depending of 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 no contraindicated 5.

Differential diagnosis

General imaging differential considerations include

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