Surgical Removal of Fibrous Dysplasia From the Craniofacial Skeleton
Alexander Govshievich
Gaby Doumit
DEFINITION
Fibrous dysplasia (FD) is a benign bone disorder characterized by progressive replacement of normal bone by abnormal fibrous tissue.
FD accounts for 2.5% of all bony tumors and 5% to 7% of all benign bony tumors.1
This disorder may be monostotic (MFD) or polyostotic (PFD), involving one or more bones. The term craniofacial fibrous dysplasia (CFD) has been used to describe FD confined to contiguous bones of the craniofacial skeleton.
PFD accompanied by café au lait spots and endocrinopathies including hyperthyroidism, Cushing syndrome, and precocious puberty, is known as McCune-Albright syndrome (MAS).
Craniomaxillofacial involvement in FD occurs in 27% of monostotic and up to 50% of polyostotic cases.2
FD can remain asymptomatic or present with pain, stress fractures, localized swelling, or deformity.
In the craniofacial skeleton, neurologic impairment can result from nerve compression by expansile FD lesions, potentially leading to blindness, deafness, or spinal cord compression.
Diagnosis is based on an accurate clinical history, physical examination, and imaging studies.
Bone biopsy is required to confirm diagnosis.
ANATOMY
Any bone of the craniofacial skeleton may be affected by FD.
Although the exact prevalence for each bone is unknown due to the relative rarity of this condition, the maxillary bone is the most frequently involved in several series.3,4,5
However, due to the compact and complex nature of the craniomaxillofacial construct, solitary FD lesions of the skull are seldom confined to individual bones, often affecting several contiguous structures.
As a result, surgical approach and treatment principles are focused on general anatomic regions rather than individual bones.
Chen et al. classified the craniomaxillofacial region into four major zones based on anatomic location, structures involved, surgical access, importance of reconstruction, and recommended treatment methods (FIG 1).6
Zone 1: Includes the frontal, nasal, ethmoidal, and zygomatic bones as well as the superior, non-tooth-bearing portion of the maxillary bone
Zone 2: Parietal, occipital, and squamous portion of the temporal bones
Zone 3: Petrous portion of the temporal bones including the mastoid process and the sphenoid bone
Zone 4: Tooth-bearing portion of the maxillary bone and the mandible and is separated into zones 4a and 4b
PATHOGENESIS
FD is a noninherited genetic disease stemming from a postzygotically occurring missense mutation in the GNAS gene.
Two mutations have been described, resulting from replacement of the arginine residue in codon 201 by either cysteine or histidine.
The mutation leads to somatic activation of the alpha subunit of signal-transducer G protein (Gs), causing increased levels of cAMP and in turn resulting in high rates of cellular proliferation.7
The abnormal proliferation and high cellular turnover produce poorly differentiated osteoblasts and immature mesenchymal cells, which are deposited within the bone and marrow of FD lesions.
Elevated cAMP levels have also been demonstrated to upregulate the growth of thyroidal, adrenal, and gonadal cell lines resulting in the characteristic endocrinopathies seen in MAS.
 FIG 1 • Subdivision of the craniomaxillofacial region into 4 major zones as described by Chen et al. |
NATURAL HISTORY
The onset and natural evolution of FD can be variable and unpredictable, largely depending on lesion type.
MFD lesions generally develop in childhood, progress through puberty, and arrest at the end of adolescence once skeletal maturity is complete.
PFD and MAS variants have been associated with more aggressive growth patterns, demonstrating younger age at presentation and continued tumor growth into adulthood. Up to 90% of these lesions may present before 15 years of age.8
Lesions seen in MAS can continue growing indefinitely, causing progressive disfigurement and functional deficits, requiring prompt surgical intervention.9,10
Pregnancy and other settings of estrogen excess such as estrogen therapy have been associated with heightened lesion growth.9,11
Spontaneous malignant transformation in FD is possible but is rare. It can be observed in MFD, PFD, and MAS forms with reported frequencies ranging from 0.5% to 6.7%.12
Any rapidly developing symptoms such as swelling or pain should raise suspicion of malignant change and prompt the appropriate investigations.
Exposure to radiotherapy has been demonstrated to be the main risk factor for malignant transformation, being associated with a 44% rate of sarcomatous change. For this reason, radiotherapy is contraindicated in patients with FD.
Osteosarcoma accounts for the majority of cases, with the remainder consisting of fibrosarcoma, chondrosarcoma, and malignant fibrohystiocytoma.13
PATIENT HISTORY AND PHYSICAL FINDINGS
Patient history should include the age at presentation, evolution of the lesion (including periods of rapid growth), and associated symptoms.
Physical examination should characterize the location of the lesion, its dimensions and any associated contour deformities, facial asymmetry, or functional deficits.
Although FD is often asymptomatic, presenting as a slowly growing, painless, and nontender swelling, it may be associated with a variety of signs and symptoms that are specific to the anatomic zone affected.
Zone 1
Hypertelorism, vertical dystopia, and exophthalmos from fronto-orbital involvement and displacement of intraorbital contents
Changes in visual acuity and blindness can result from impingement of the optic nerve by lesions invading the anterior cranial fossa
Nasal obstruction and recurrent sinusitis can be caused by sinus involvement (FIG 2)
Facial asymmetry secondary to tumor enlargement
Zone 2
Headaches and elevated intracranial pressure (ICP) may result from calvarial involvement.
Cranial vault asymmetry secondary to tumor growth
Macrocephaly
Zone 3
Otalgia, fullness, conductive hearing loss, and cholesteatoma formation from external auditory canal (EAC) involvement
FIG 2 • Lateral (A) and anterior (B) views of a patient with large lower zone 1 fibrous dysplasia. Important nasal airway involvement is seen.
Vertigo, tinnitus, sensorineural hearing loss, or facial nerve paralysis from invasion of the inner ear and internal auditory canal
Visual disturbances or blindness with a lesion affecting the sphenoid bone
Zones 4a and 4b
Displacement of teeth, vertical maxillary excess, or malocclusion
Patients with lesions neighboring the orbit, namely, those in zones I and III, must be followed with serial visual acuity and visual field measurements to rule out impingement of the optic nerve. Conduction of neuroophthalmological studies is also recommended.
Given that craniofacial FD can be part of PFD or MAS, the primary clinical assessment should include a full body examination looking for any additional bony lesions, café au lait spots, or findings suggestive of hyperthyroidism, Cushing syndrome, or precocious puberty.
When suspected, a multidisciplinary approach with an endocrinologist is recommended for further investigations and follow-up.
IMAGING
Radiologic investigation should be conducted in all patients with FD.
Radiologic appearance of lesions demonstrates three radiologic patterns, namely, pagetoid, sclerotic, and cystic.13 Mixed changes also can be seen.
Standard roentgenography is of limited diagnostic use in FD. Images can demonstrate expanded bone with groundglass appearance, widened diploic space with displacement of the outer table and sparing of the inner table, cystic skull vault lesions, obliteration of paranasal sinuses, or dental malocclusions.
High-resolution CT (1-mm cuts) is the preferred imaging modality, providing useful information for diagnosis, follow-up, and surgical planning. Three-dimensional (3D) reconstruction can further assist in surgical planning.
Images obtained with CT scan:
Provide more accurate information regarding lesion size, location, surrounding structures, and potential compression sites (FIG 3).
Appearance is related to lesion age, with younger lesions appearing more radiolucent and mature lesions appearing
more opaque. Ground-glass appearance is seen in established lesions and often represents the best diagnostic clue.9
FIG 3 • CT scan of patient with large lower zone 1 fibrous dysplasia. A. Sagittal cut. B. Coronal cut. C. 3D reconstruction.
Bones affected by FD are usually expanded with intact cortices. Normal corticomedullary differentiation is lost. The margin between abnormal and normal bone is often difficult to identify because the two regions blend into each other.
MRI is of lesser diagnostic value than CT. Image appearance is variable, depending on the degree of lucency vs sclerosis.
T1- and T2-weighted images generally demonstrate a heterogeneous appearance or decreased signal.
Injection of contrast demonstrates variable enhancement, which depends on lesion type.
Bone scan has a very limited diagnostic role in FD; however, images can provide useful information regarding the presence of secondary lesions in the setting of PFD. Radionuclide uptake is variable.
DIFFERENTIAL DIAGNOSIS
Paget disease of bone
Cherubism
Interosseous meningioma
Garré sclerosing osteomyelitis
Cemento-ossifying fibroma
Craniometaphyseal dysplasia
Sclerotic metastasis
NONOPERATIVE MANAGEMENT
Nonoperative treatment in FD can be twofold, including expectant management or medical therapy.
Expectant management is appropriate in most cases, particularly when lesions are small, slowly growing or static, asymptomatic, and causing minimal functional or aesthetic deficits.
Regular follow-up and routine annual checkups with CT imaging are required to assess for progression or development of complications.
Medical therapy is primarily aimed at providing symptomatic relief and can be used as an adjunct to surgery.
Acetaminophen and NSAIDs
Used for mild bone pain
Narcotics
Used for more severe bone pain
Bisphosphonates
Inhibit osteoclast activity, thus improving bone density and potentially delaying progression of lesions into adjacent structures.4
Reduce pain associated with FD, improve radiologic appearance of lesions, and decrease biochemical markers of bone remodeling (ie, serum ALP).14
Typically used in more severe cases such as those seen in MAS.
The most commonly used agent is pamidronate and is administered intravenously every 6 months (180 mg for adults and 3 mg/kg in children and adolescents).
Alendronate and zoledronate have also been used.
Monoclonal antibodies
The most commonly used agent is tocilizumab.
Decreases IL6 levels and subsequent osteoclast activity by binding to IL6 receptors.
Used for pain reduction in patients that fail to respond to bisphosphonate treatment.
Calcium, phosphate, and vitamin D supplementation can be useful in patients with deficiencies or mineralization defects such as hyperparathyroidism, osteomalacia, and renal phosphate wasting.
SURGICAL MANAGEMENT
Surgery is the mainstay of treatment for symptomatic FD and is the only definitive treatment modality.
Because of the complexity of the craniofacial skeleton and the important structures it contains, a multidisciplinary team including otolaryngology, ophthalmology, neurosurgery, and plastic surgery is required.
The presence of FD alone is not an indication for surgery because many lesions remain static and asymptomatic and are often found incidentally with CT imaging.
Indications for surgery include the presence of pain not controlled by medical therapy, significant aesthetic deformity, functional deficit (ie, optic nerve compression), rapidly growing lesions, or malignant transformation.
Surgical approaches are generally divided into shaving/contouring procedures, subtotal/partial resections, and total or wide excisions.
Total resection of dysplastic bone is the preferred treatment modality (for rapidly growing, malignant, or recurrent lesions), minimizing the risk of recurrence and subsequent need for revisional surgeries. However, total resection may not be feasible, particularly in extensive CFD lesions where wide resection can significantly increase morbidity and the risk of complications.
It is of paramount importance to ensure that the defect caused by the procedure does not cause a greater functional or aesthetic deficit than present before surgery. Risks
and benefits should be clearly described to patients and families.
No guidelines exist for surgical management of FD. Treatment should be personalized and guided by the patient’s age, lesion characteristics (location, extent, and evolution), and the presence of any functional or aesthetic deficits.
Bone biopsy must be obtained before surgical intervention when diagnosis is uncertain or when there is concern for malignancy.
Timing of intervention:
Defer surgical procedures until lesion growth subsides and skeletal maturity is attained.
Earlier intervention may become necessary if progressive expansion of the lesion causes significant functional, aesthetic, and psychological disturbances to the affected child.
Conservative shaving is recommended in these cases. However, patients should be informed that recurrence is possible and further contouring procedures may be required, particularly in cases of PFD and MAS, where continued growth is anticipated.
Conversely, if severe deformity is present, which cannot be corrected by contouring, radical excision and reconstruction is indicated. Patients should be made aware that recurrence is possible despite a wide excision.
In the adult population, static lesions causing a contour deformity can be appropriately managed by shaving of the lesion. The presence of a functional deficit (such as airway obstruction, oral obstruction or optic nerve compression, etc.) warrants a more radical resection or an en bloc resection, when feasible, and immediate reconstruction.
Zone 1
Represents the most cosmetically sensitive part of the face and is of particular relevance to the craniofacial surgeonRelated posts:
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