Fibrous Dysplasia
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First described by Von Recklinghausen (1891)
characterized by expanding fibroosseous tissue within affected bones and
predominantly is a lesion of the growing skeleton.
Gross appearance of diseased tissue is gray-white or gray-red, with a gritty
texture.
Definition
 Fibrous dysplasia is a skeletal developmental anomaly of the bone-forming
mesenchyme that manifests as a defect in osteoblastic differentiation and
maturation.
 Non neoplastic, benign disease of bone whereby lamella bone does not form, but
is instead replaced by dysplastic fibrous tissue and immature woven bone
Aetiology
 nonhereditary disorder
 caused by sporadic mutation in the postzygotic stage , of the GNAS1 gene that
encodes the alpha subunit of the stimulatory G protein (G1)- stimulates cAMP
 Once activated, the mutated Gs alpha subunit remains activated for a prolonged
period – leads to constant stimulation cAMP
 The specific phenotype depends on the cell type containing the mutation
 The earlier the mutation occurs in embryogenesis, the more widespread the tissue
involvement.
 likely that activating Gsa mutations are lethal if they occur very early in
embryogenesis. This would account for the lack of autosomal dominant
transmission of this syndrome.
 2 theories
1. disorder of postnatal cancellous bone maintenance in which bone
undergoing physiologic remodeling is replaced by an abnormal
proliferation of fibrous tissue
2. arrest of bone maturation in the woven bone stage, forming
irregularly shaped trabecula.
Classification
1. Monostotic
a. Most common form (70-80%)
b. in decreasing order of frequency - rib (28%), femur (23%), tibia,
craniofacial bones 10-25%, and humerus
c. may present with pain or a pathologic fracture, usually 1st-3rd decade
d. degree of bone deformity is relatively less severe compared with that of
the polyostotic type
e. becomes inactive after age 30. It may reactivate during pregnancy.
2. Polyostotic
a. 20-30%
b. femur (91%), tibia (81%), pelvis (78%), ribs, skull and facial bones (50%),
upper extremities, lumbar spine, clavicle, and cervical spine, in decreasing
order of frequency.
c. Two thirds of patients are symptomatic before they are 10 years of age –
pain or pathological fracture
d. typically remains active throughout life
e. Cutaneous pigmentation occurs in 50% (cafe-au-lait spots) - in polyostotic
fibrous dysplasia is ipsilateral to the side of bony lesions, a feature that
differentiates this from pigmentation in neurofibromatosis.
3. Craniofacial form
a. occurs in 10-25% of patients with the monostotic form and in 50-100%
with the polyostotic form.
b. most common - frontal, sphenoid, maxillary, and ethmoidal bones
c. does not typically cross midline
d. tends to be more osseous than fibrous dysplasia of other sites
4. Cherubism
a. autosomal-dominant disorder of variable penetrance (100% penetrance in
males)
b. Bilateral symmetrical maxilla and mandible swelling
c. Usually begins with eruption of secondary dentition (age 2-4)
d. stabilizes after the growth period
e. strictly a self-limiting disease of children that regresses without surgery
and leaves no deformity.
f. May leave some facial deformity and malocclusion.
Associations
1. McCune-Albright syndrome (3-5%)
a. Polyostotic fibrous dysplasia
b. precocious puberty – usually in girls, menarche at 3yrs old
c. cutaneous café au lait spots (50%) with jagged "coast of Maine"
border, stops at midline (café au lait spots usually have smooth border
– coast of California)
2. endocrinopathies (2-3%)
a. precocious puberty in girls, hyperthyroidism,
hyperparathyroidism, acromegaly, diabetes mellitus, and Cushing
syndrome.
Problems
 Pathologic fractures
 Pain – due to deformity, structural weakening
 Deformity
 Metabolic changes
o Hypophosphatemic rickets and osteomalacia
 Malignant degeneration
o <1% (30 case reports)
o Radiation therapy is an important risk factor (50%)
o Osteogenic sarcoma most common, fibrosarcoma and chondrosarcomas
occur less frequently.
o Suspect if rapid increase in the size of the lesion, increasing pain and a
change from a previously mineralized bony lesion to a lytic lesion.
o CT will show local destruction and lytic areas
o Blood test – elevated ALT
Craniofacial problems
 Orbital bones - Hypertelorism, cranial asymmetry, facial deformity (ie, leontiasis
ossea), visual impairment, diplopia, extraocular nerve palsy, proptosis, dystopia,
and blindness
 Nasal bones - nasal obstruction, sinusitis, epistaxis, epiphora - occlusion of the
lacrimal duct
 Sphenoid wing and temporal bones - vestibular dysfunction, tinnitus, and hearing
loss, facial paralysis
 cribriform plate - hyposmia or anosmia may result.
 Mandible – occlusion, dentition, deformity, oral obstruction
Involvement around the orbital apex may be difficult to differentiate from orbital
meniogioma (Hansen J Craniofacial Surg 1994)
1. Fibrous dysplasia commences in childhood and early adolescence while
meningiomas are diseases of middle age.
2. Visual symptoms are prominent in meningioma cases, while uncommon in fibrous
dysplasia.
3. Proptosis is much more marked than orbital dystopia in the meningioma
group while the reverse is true in fibrous dysplasia.
4. Fibrous dysplasia patients have extensive frontal bone involvement that is
clinically obvious. There is no evidence of this in meningioma patients.
5. Pain is present in both groups and is not a useful discriminating feature.
Radiology
 usual appearance on xray
o a lucent homogenous lesion in the diaphysis or metaphysic (ground glass)
o endosteal scalloping
o with or without bone expansion
o absence of periosteal reaction.
Management
 Unless there are functional problems, wait until skeletal maturity whence disease
will burn out in monostotic form
 Treat endocrine abnormalities
 May respond to tamoxifen, biphosphonates.
Indications (craniofacial)
1. pain
2. pathologic fracture
3. to rule out malignancy
4. functional considerations
a. vision and hearing
b. sinus and nasal obstruction, epistaxis
c. malocclusion, and mastication.
5. cosmetic deformity
Indications for surgical decompression of orbit
1. progressive gradual visual loss
2. within 1 week of sudden visual loss
3. children or adolescents with no visual loss but radiographic evidence of optic
canal reduction, since they are likely to have progressive growth of fibrous
dysplasia
Surgical
 In the past conservative treatment was preferred.
1. Bone contouring
2. Curettage and replacement of the bone defect with autograft or allograft
o May result in resorption of the graft into fibrous dysplasia.
o Use of allograft or cortical autograft usually delays this conversion, as it is
more resistant to resorption and replacement by dysplastic bone
o Edgerton describes use of the dysplastic bone as grafts, which following
resection were contoured, thinned, and replaced.
o Others have autoclaved or cryotherapied the dysplastic bone prior to
grafting
o
3. Radical resection
o Chen and Noordhoff (PRS 1991) recommendations:
1. radical resection and reconstruction for most visible facial parts –
frontal, orbital, nasal, ethmoid and zygoma, upper maxilla
2. conservative or radical resection for hair covered cranium
3. observation for difficult or dangerous areas – central cranial base,
petrous, mastoid, pterygoid, sphenoid
4. conservative excision for tooth bearing bones - lower maxilla and
mandible
o Large functional defects (mandible) will need vascularised reconstructions
ie fibula flap
Postop
Needs long term followup