Clinical features

Three-quarters of patients with orbital FD have the monostotic form affecting several contiguous bones but the disease usually remains unilateral. The craniofacial area is affected in 20% of patients, with a predilection for the frontal, sphenoid, and ethmoid bones. Typically, there is a painless, firm, bony swelling with contour distortion; in the orbit, there is an accompanying mass effect. The clinical presentation depends on the predominant wall involved, most commonly the roof, resulting in proptosis and downward displacement of the globe and orbit.^5,6 The lacrimal fossa may be affected, mimicking a lacrimal gland tumor.⁷ Maxillary disease (Fig. 25.1) displaces the eye upwards, with persistent epiphora if the nasolacrimal duct is affected.⁸ Sphenoid involvement results in optic nerve compression^5,6 from narrowing of the optic canal (Fig 25.2) or by an associated sphenoid sinus mucocoele.⁹ Rarely, involvement of the sella turcica may result in chiasmal compression.¹⁰ Other uncommon neuro-ophthalmic complications include cranial nerve palsies,¹¹ trigeminal neuralgia, raised intracranial pressure, and papilledema.^11,12 Extensive craniofacial involvement can result in severe cosmetic deformity. Pain may occur, either localized or as a diffuse ipsilateral headache. Visual loss is not uncommon.^5,13 Malignant transformation to osteosarcoma, fibrosarcoma, chondrosarcoma, and giant cell sarcoma occurs in 0.5% of cases increasing to 15% with prior radiotherapy.¹³ The accompanying signs are rapid progression, worsening pain, and infiltration of surrounding structures.

Fig. 25.1 (A) This 16-year-old presented with a history of progressive facial distortion and decreasing vision in the left eye to 20/40. Compressive optic neuropathy was diagnosed secondary to fibrous dysplasia. (B) CT scan of the same case showing cystic fibrous dysplasia involving the orbital apex. (C) Axial CT scan shows optic canal involvement. This was surgically decompressed.

(Patient of the University of British Columbia.)

Fig. 25.2 (A, B) Fibrous dysplasia. CT scan showing sphenoid involvement. The optic canals are narrowed. (C, D) Same patient: there was chronic compressive optic neuropathy with atrophy on the left. This patient presented with decreased vision at 12 years of age and she showed no deterioration 2 years later with minimal residual signs or symptoms; she was not treated.

The main radiographic feature of FD is expansion of bone. The lesions may be sclerotic, with a dense ground-glass homogeneity, lytic, with increased lucency, or show a mixed picture with alternating areas of lucency and increased density. Most orbital cases are easily diagnosed since they are sclerotic.⁵ The main radiologic differential diagnosis includes histiocytosis-X, hyperostotic meningioma, Paget’s disease (both rare in children), and some bone tumors. On magnetic resonance imaging (MRI) there is a correlation between T1 and T2 signal intensity and clinical and pathologic activity of the lesion.¹⁴ Occasionally, large cystic lesions form in the orbital wall.⁵ These may contain blood (Fig. 25.3) and necrotic debris and can be mistaken for aneurysmal bone cysts.¹³ Involvement of a neighboring sinus may mimic mucocele.^13,15 Computed tomography (CT) scanning with the possible addition of MRI is the best modality to evaluate the extent of cranial and orbital involvement. The optic canal and chiasm should be assessed for signs of compression.

Fig. 25.3 (A) This 22-year-old developed sudden proptosis of the right eye after a history of slowly progressive facial asymmetry from early childhood. (B) CT scan showed the fluid level of a hemorrhage within the cystic dysplastic bone. The diagnosis was fibrous dysplasia.

(Patient of the University of British Columbia.)

Management

FD is usually benign and self-limiting. However, the final extent and time of arrest of the lesion are unpredictable. Treatment aims to prevent complications, especially optic nerve compression, and improve cosmesis while waiting for spontaneous arrest.

When there is little doubt about the diagnosis, initial observation and repeat radiologic assessment is best. If the lesion in the orbital wall is lytic or cystic, biopsy is usually necessary to confirm the diagnosis. Outside the orbit, the risk of malignant change after radiotherapy is high¹⁶ and is not used.

Surgery is indicated for cosmetic disfigurement, intractable pain, or optic nerve compression. Since dysplastic bone can be vascular, preoperative blood cross-matching is advisable. Resection of dysplastic bone around the optic canal can reverse visual loss of early compressive optic neuropathy.^9,13 Steroids may also be useful.¹⁷ When decompressing the optic nerve, rongeurs rather than high speed drills (heat producing) should be used to protect the nerve. Surgery traditionally consisted of de-bulking the lesion. However, the margins of the affected bone are difficult to define clinically and recurrence was common.⁶ In the last 20 years, there has been a shift toward more radical excision of all diseased bone and immediate facial and orbital reconstruction using bone grafts^5,18 by combined ophthalmology/craniofacial teams. Whilst some groups report no visual function deterioration following early optic canal decompression, there have been reports of blindness complicating prophylactic nerve decompression.¹⁹ Visual loss is not usually the result of progressive optic canal stenosis but from the rapid expansion of cystic components, FD mucoceles, or hemorrhage.²⁰ Prophylactic optic canal decompression is not indicated and a conservative approach is warranted, reserving optic canal decompression for patients with progressive or sudden deterioration of visual function.²¹