Fibrous Dysplasia of the Maxilla and Mandible

Definition and Pathogenesis

• Cummings Otolaryngology, p. 2917 | Scott-Brown's ORL, p. 1148

Classification

• KJ Lee's Essential Otolaryngology, p. 1232 | Harrison's Principles, p. 3361

Clinical Features

• Most commonly diagnosed in the first two decades of life
• Equal sex frequency overall; MAS with precocious puberty is 10:1 female predominance
• Monostotic form may become quiescent at puberty; polyostotic form can continue progressing
• Lesions may reactivate during pregnancy or with estrogen therapy

• Diffuse, painless bony swelling with facial deformity - the hallmark presentation
• Does not cross the midline
• Facial asymmetry and malocclusion
• Dental displacement; involves and incorporates the lamina dura and cortical bone
• Nasal obstruction and sinusitis (maxillary sinus encroachment)
• Orbital displacement causing proptosis or diplopia
• Optic nerve compression from orbital roof or sphenoid involvement - a serious complication
• In advanced cases: pain, pathological fracture, cranial nerve palsies
• Leontiasis ossea (lion-face deformity) in severe craniofacial involvement

• Café-au-lait spots with rough "coast of Maine" borders (vs. smooth "coast of California" borders in neurofibromatosis)
• Precocious puberty (most common endocrinopathy)
• Less common: thyrotoxicosis, Cushing's syndrome, acromegaly, hyperparathyroidism

Radiological Findings

• Classic: ground-glass appearance with fusiform, tapered expansion and diffuse margins
• May also appear as: multilocular radiolucency, radiolucent/lytic, or irregularly mottled (mixed opaque and lucent)
• Involves and incorporates the lamina dura and cortical bone (unlike ossifying fibroma)
• The lesion blends with surrounding bone without a discrete capsule

• Appearance depends on degree of mineralization:
  • Early/high fibrous content: radiolucent/lytic appearance
  • As mineralization increases: ground-glass (most characteristic)
  • Advanced: sclerotic/dense
• Expansile lesion with mixed density; no sharp peripheral cortical rim (unlike ossifying fibroma)
• Involvement of the maxillary sinus walls, orbital floor, and skull base can be assessed

Axial CT: expansile fibrous dysplasia lesion (T) in the sphenoid showing ground-glass appearance (arrowheads) and low-density areas (asterisks) - Cummings Otolaryngology

Lateral skull X-ray showing lytic (L) and fibrous (F) phases; ground-glass appearance from disorganized woven bone spicules - Cummings Otolaryngology

• Variable T2 signal (reflects varying degrees of mineralization)
• T1: commonly hypointense
• Non-homogeneous enhancement with gadolinium

Histopathology

• Stroma: cellular, spindle-cell fibrous tissue
• Trabeculae: curvilinear, disconnected woven bone (like "Chinese letters" or alphabet soup)
• No osteoblastic rimming of bone trabeculae (important!)
• No lamellar bone
• Diagnosis cannot be made by microscopy alone - requires correlation with clinical and radiographic findings

Differential Diagnosis

Laboratory Findings

• Serum alkaline phosphatase (ALP) elevated in ~30% of polyostotic cases
• Serum calcium, phosphorus, PTH, 25-OH vitamin D: usually normal
• Extensive polyostotic lesions: may cause hypophosphatemia + hyperphosphaturia + osteomalacia (due to FGF23 overproduction by dysplastic tissue)
• Biochemical markers of bone turnover may be elevated

Treatment

• Asymptomatic patients should be followed with periodic clinical and radiological examinations
• Monostotic FD can often be observed; lesions tend to stabilize after skeletal maturation
• Surgery should be postponed as long as possible in younger, asymptomatic patients

• Bisphosphonates (IV): Reduce bone pain and may partially resolve radiographic lesions; reduce fracture risk
• Denosumab: Monthly or every 3 months; effective in reducing bone turnover markers; note - discontinuation can occasionally result in rebound hypercalcemia (per Harrison's 22nd ed., 2025)
• No role for radiotherapy - it is ineffective and increases risk of malignant transformation

1. Visual impairment (optic nerve compression)
2. Cosmetic/aesthetic deformity
3. Sinus obstruction causing sinusitis
4. Pathologic fracture risk or destruction of joint space
5. Cranial nerve compression

• Endoscopic sinus surgery for paranasal sinus lesions - improves drainage, relieves sinusitis; ideally with computer-assisted navigation
• Local controlled resection and bone recontouring (not radical excision) for cosmetic deformity
• In contrast to ossifying fibroma, wide radical resection is NOT required for FD

Complications and Prognosis

• Sarcomatous transformation: Rare; estimated at 0.4-0.5% (osteosarcoma most common)
  • Any rapidly growing, painful lesion should raise suspicion
  • Risk is increased by radiation (never irradiate FD)
• Lesions typically stabilize after skeletal maturity
• Polyostotic form can continue progressing into adulthood
• Renal phosphate wasting with rickets/osteomalacia in widespread disease

Key Distinguishing Points for the Maxilla vs. Mandible

• Maxilla is the most commonly involved jaw bone in craniofacial FD, particularly in polyostotic disease
• Maxillary FD can obliterate the maxillary sinus, encroach on the orbit, and involve the pterygoid plates
• Mandibular FD is less common; when the mandible is the sole site in children, consider cherubism (which bilaterally involves mandible and maxilla but spares the condyles)
• The juvenile aggressive variant almost exclusively involves the maxilla - rapidly growing, destroys tooth buds, and is refractory to treatment

Recent evidence note (2026): A systematic review (PMID 41955566, J Clin Endocrinol Metab, June 2026) from the ECTS Rare Bone Disease Action Group reviewed denosumab use in rare bone diseases including fibrous dysplasia. Its findings support denosumab as an option when bisphosphonates are insufficient, consistent with Harrison's 22E guidance above.

Fibrous Dysplasia of the Maxilla and Mandible

Definition and Pathogenesis

• Promotes cellular proliferation
• Disrupts osteoblast differentiation
• Prevents maturation of bone to lamellar structure

• Robbins & Kumar Basic Pathology, p. 789 | Scott-Brown's ORL Vol. 1, p. 1148

Classification

Ossifying fibroma and FD were historically grouped together due to histologic overlap, but Reed (1963) separated them. FD is a genetic developmental anomaly; ossifying fibroma is a true benign neoplasm. The key histologic difference is the absence of a capsule and lack of osteoblastic rimming in FD.

• Cummings Otolaryngology, p. 996

Clinical Features

• Presents in the first to second decade of life
• Equal sex frequency overall; MAS with precocious puberty is 10:1 female predominance
• Monostotic form often becomes quiescent at skeletal maturity (puberty); polyostotic can progress into adulthood
• Early-onset disease is generally more severe
• Lesions may reactivate during pregnancy or with estrogen therapy

• Diffuse, painless bony swelling causing facial deformity - the cardinal presentation
• Does not cross the midline
• Facial asymmetry and malocclusion
• Loose dentition; incorporates and displaces the lamina dura
• Mass of the body of the mandible or alveolar ridge of maxilla
• Paresthesias, pain (if nerve involved)
• Maxillary: nasal obstruction, sinusitis, sinus drainage obstruction
• Maxillary/orbital: proptosis, diplopia, epiphora
• Optic nerve compression from orbital roof or sphenoid extension - a sight-threatening complication
• Headache, facial pressure

• Café-au-lait spots with rough "coast of Maine" borders (vs. smooth "coast of California" in neurofibromatosis)
• Isosexual pseudoprecocious puberty (most common endocrinopathy - girls >> boys)
• Less common: thyrotoxicosis, Cushing's syndrome, acromegaly, hyperparathyroidism, hyperprolactinemia
• Leontiasis ossea (lion-face appearance) in severe craniofacial involvement
• Skull base foraminal narrowing causing hearing loss, visual loss, or other cranial nerve deficits

Radiological Features

• Classic: ground-glass appearance with fusiform, tapered expansion and diffuse margins (no discrete capsule)
• Also: multilocular radiolucency, lytic, or irregularly mottled (mixed opaque and lucent)
• Involves and incorporates the lamina dura and cortical bone (key point - does not displace or thin the cortex as a separate rim)
• Lesion blends imperceptibly with surrounding bone

Lateral skull radiograph: lytic (L) and fibrous (F) phases of fibrous dysplasia - Cummings Otolaryngology

• Appearance tracks degree of mineralization:
  • Early/high fibrous content → radiolucent/lytic (mimics simple bone cyst)
  • Intermediate mineralization → ground-glass (most characteristic and diagnostic)
  • Advanced mineralization → cotton-wool / sclerotic
• Expansile lesion; no sharp peripheral eggshell cortical rim (ossifying fibroma has this)
• Useful for: sinus obliteration, orbital involvement, skull base foraminal compromise, optic canal narrowing

Axial CT: expansile FD of the sphenoid with characteristic ground-glass + low-density mixed pattern - Cummings Otolaryngology

• T1: intermediate signal (hypointense in many cases)
• T2: hypointense (helpful to distinguish from meningioma and bone cysts, which are T2 bright)
• Non-homogeneous gadolinium enhancement
• Useful to evaluate soft tissue component and nerve compression

Histopathology

• Fibrous stroma arranged in a whorled pattern
• Woven bone spicules are irregular, disconnected, curvilinear
• No rim of osteoblasts around bone trabeculae (critical distinction from ossifying fibroma)
• No lamellar bone maturation
• Cystic degeneration, hemorrhage, and foamy macrophages may be present
• No capsule (contrast: ossifying fibroma is capsulated)
• Periosteal reaction: usually absent

"Diagnosis is often impossible by microscopy alone and requires clinical and radiographic information." - KJ Lee's Essential Otolaryngology

Histology: curvilinear woven bone trabeculae without osteoblastic rimming in a cellular fibrous background - Robbins & Kumar Basic Pathology

Laboratory Findings

• Serum alkaline phosphatase (ALP) elevated in ~30% of polyostotic FD cases
• Serum calcium, phosphorus, PTH, 25-OH vitamin D: usually normal
• Extensive polyostotic lesions: hypophosphatemia + hyperphosphaturia (due to FGF-23 overproduction by dysplastic tissue) causing rickets or osteomalacia
• Biochemical markers of bone turnover may be elevated

Differential Diagnosis

Treatment

• Asymptomatic monostotic FD can be observed with periodic clinical and radiological follow-up
• Lesions tend to stabilize after skeletal maturation; surgery should be deferred as long as possible in asymptomatic children

• IV bisphosphonates - reduce bone pain, reduce fracture incidence, may partially resolve radiographic lesions
• Denosumab (monthly or every 3 months) - reduces bone turnover markers; note that discontinuation can trigger rebound hypercalcemia

1. Visual impairment / optic nerve compression
2. Cosmetic/aesthetic deformity
3. Sinus obstruction causing chronic sinusitis
4. Pathologic fracture risk or joint destruction
5. Cranial nerve compression (hearing loss, etc.)

• Endoscopic sinus surgery for paranasal sinus involvement - improves drainage; computer-assisted navigation is preferred
• Local controlled resection + bone recontouring for cosmetic deformity - not radical resection (unlike ossifying fibroma)
• Wide radical excision is NOT indicated; FD does not have sharp margins and recontouring is the goal

No role for radiotherapy - it is ineffective and significantly increases the risk of malignant transformation. Never irradiate FD.

Complications and Prognosis

• Sarcomatous transformation: ~0.4-0.5%; osteosarcoma most common
  • Risk significantly increased by prior radiation therapy
  • Suspect in any rapidly growing or painful lesion
• Monostotic FD: generally stabilizes at skeletal maturity; favorable prognosis
• Polyostotic FD: may progress into adulthood; more complications
• Renal phosphate wasting (FGF-23 mediated) in widespread disease

Maxilla vs. Mandible: Specific Points

• Most commonly involved jaw bone in craniofacial FD, especially in polyostotic disease
• Can obliterate the maxillary sinus entirely, erode the orbital floor, and extend to the pterygoid plates and skull base
• The juvenile aggressive variant almost exclusively affects the maxilla - rapidly growing, destroys tooth buds, and is refractory to treatment
• Orbital/optic nerve complications are more likely with maxillary involvement

• Less commonly involved than maxilla in FD
• Presents as painless swelling of the body of the mandible
• When bilateral mandibular FD occurs in children, always consider Cherubism (inheritable, autosomal dominant, spares condyles - unlike conventional FD)
• Monostotic mandibular FD: relatively better prognosis; often stabilizes at puberty

Recent literature (2025): A systematic review on craniofacial FD (Tuompo et al., Bone, Mar 2025; PMID 39681203) provides an updated synthesis of diagnosis and management of craniofacial FD - the most relevant recent evidence for this topic.