Visual Field Improvement Achieved by Decompression Surgery for Craniomaxillofacial Fibrous Dysplasia: A Case Report

Background Craniomaxillofacial brous dysplasia (CFD) is a type of congenital benign bone disorder that progressively replaces the healthy bone marrow with brous tissue. When the optic nerve is inuenced, the ecacy of therapeutic decompression is doubtful, as vision loss is irreversible with the thinning nerve ber layer. Case presentation A 22-year-old female presented to our institution with left painless, slowly-progressing orbito-fronto-temporal swelling. She had undergone several plastic surgeries before. Enlargement in her left frontal area involving the orbital region was seen, with increased frontal contour and vertical dystopia and minimal inferior displacement of the globe. We observed signicant visual eld defects in her left eye, and her retinal ber layer was thin on examination. She was therefore diagnosed as FD. Decompression operation was performed, and her visual acuity and central visual eld improved in the 1-month follow-up. Conclusions Our case indicated that visual defect caused by prolonged time course of optic nerve compression by craniomaxillofacial brous dysplasia can be relieved partially by decompression surgery.


Introduction
Fibrous dysplasia (FD) is a non-neoplastic, non-hereditary, and congenital benign bone disorder that progressively replaces the healthy bone marrow with brous tissue, accompanied by thinning of cortical bone [1,2]. Typically, FD was classi ed by the sites of pathological changes. Among them, the craniofacial region deformation is the most frequent [2]. Clinically, progressive swelling in affected area without pain was the most common chief complaint [3]. Other symptoms may include facial asymmetry, pathological fractures, and nerve compression [4,5]. With deformation of the ocular bones, the optic canal becomes fragile due to its location in the center area. The e cacy of therapeutic decompression is doubtful as the previous study showed its failure to reverse the vision loss if the nerve ber layer has displayed signs of damage in relevant ophthalmic examinations [2]. Regarding this, we reported a case of craniomaxillofacial brous dysplasia (CFD) with optic canal involved. Contracted visual eld caused by compression to the optic nerve signi cantly improved after decompression surgery.

Case Presentation
A 22-year-old female presented to our institution with left painless, slowly-progressing orbito-frontotemporal swelling in May 2018. At the age of ve, her family noticed her forehead protuberance in the left Page 3/9 face for the rst time and referred to the local hospital. She was then diagnosed as FD and underwent surgeries to improve her appearance. However, as residual diseases continued to enlarge, optic nerve was compressed and progressive contraction of visual eld was found in her left eye afterward. She suffered from diplopia and exotropia caused by the exophthalmos and mandibular protrusion. Disorder of the upper and mandibular occlusion worsened as her facial asymmetry grew. The progression nally ceased at the age of 12, and over the past ten years, her symptoms remained stable. During the process, there was no evidence of endocrinological disorders or an apparent decline in her visual acuity. She began to seek further treatment for cosmetic purposes two years ago. Her maxillofacial malformation improved after three more surgical remodeling procedures on the left maxillary bone and mandibular zygomatic region. As her vision-threatening orbital deformities remained, she was referred to us for further ophthalmic treatments.   Therefore, CFD was further con rmed. Reconstruction of the left eye socket was performed to improve her deformity. Under general anesthesia, bone tissue of the inner orbital wall was found proliferated, and the ethmoid sinus had disappeared. We therefore removed the bone tissue from the outer orbital wall to the apex of the orbit. (Figure.

Discussion And Conclusions
FD is a benign lesion with a low rate of malignancy. Typical classi cation of FD includes three variants: monostotic, polyostotic, and McCune-Albright syndrome (associated with endocrinopathies and skin hyperpigmentation) [2,6] . CFD usually starts in infancy. After a slow growth, typical symptoms will appear in childhood or adolescence. It will then enter a stable stage and nally stop processing during adulthood.
However, in a small proportion of cases, the course of the disease can reach 70 years [7] . In this case, the 22-year-old patient suffered signi cant facial deformities. She had a long history of progression, but facial deformity, visual acuity, and visual eld remained stable about ten years ago. Her disease course was typical.
For the diagnosis of FD, clinical, radiographic, and histopathological features are usually necessary.
Besides, examinations, including visual acuity, visual eld, color vision, and VEP tests are crucial for ophthalmologists. Pathologically, spindle cells surrounded by a brous matrix will replace the normal bone [8] . CT representation of FD consists of three varieties: pagetoid, or ground-glass pattern (56%), sclerotic lesions (23%) and cystic variety (21%) [9] . The characteristics of FD in CT include the expansion of the involved bone with a heterogeneous pattern of CT densities associated with scattered or con uent islands of bone formation. Speci cally, almost all CT ndings of CFD show the glass-like changes [10] .
Hence, it is usually the rst choice to choose CT for the examination of CFD. As for our patient, our CT results showed a homogenous, "ground-glass" lesion, with a left predominant expansion of the ethmoid and the temporal bone. CT images after the surgery presented our removal of the mass. Differential diagnosis should include nonossifying broma, brous dysplasia of bone, aneurysmal bone cysts, osteoma, giant cell tumor of bone, low osteosarcoma, low degree chondrosarcoma, and fracture healing.
History, location, and biopsy are essential for the identi cation of certain diseases [1] .
There are no standard treatments for FD currently, but it is recognized that tailored approaches according to the characteristics of the patient will be more appropriate. Surgical treatments will be required when symptoms occur and progress, especially when bothering one's daily activities. If the optic nerve is involved, either therapeutic or prophylactic decompression should start as soon as possible. Prophylactic decompression is performed to avoid further progression of visual loss caused by compression of optic canal stenosis, but the loss of vision is still di cult to control. While the effect of therapeutic decompression remains controversial, some experts believe that if the thickness of the retinal nerve ber layer is in normal status, visual function can recover after decompression. On the contrary, if the nerve ber layer has thinned, decompression cannot reverse the process, and the decline in visual acuity will progress [2] . The aims for surgical treatment are not only for cosmetic purposes but also to restore the physiological function of the affected organ. Although FD is usually of the multi-bone type involves a wide range of bones without clear boundaries, the recurrence rate is low in adult patients. Orbital bones will be removed to expose the surgical area, but extensive resection can lead to severe secondary deformities and damage to facial function. Therefore, su cient hemostasis and precise operation are necessary to prevent accidental injury to the optic nerve. Otherwise, visual acuity may be irreversibly damaged.
During our examination, VEP displayed a functional loss of visual pathway, while OCT proved the structural damage to the optic nerve. After the removal of an appropriate amount of orbital bone during surgery, her appearance considerably improved. Surprisingly, visual acuity was preserved, and we observed an overall improvement in her visual function. Besides, the central visual eld area enlarged at one month after surgery. Other than emergent decompression to salvage one's vision [11] , our case indicated that even when the compression has damaged the optic nerve for a prolonged disease course, relieving the compression can still improve visual function partially. Possible explanation was that the central visual eld might be recently affected, which was therefore reversible. However, overall or quadrant thickness of retinal nerve ber, which was most commonly used to assess the structure of optic nerve, could not distinguish that. Such phenomenon further displayed the importance of early decompression surgery in order to salvage the potential function of vision.
The patient's eye position was still oblique after surgery, and the left eye was not able to turn inward, which was one of the limitations of our treatments. We believed that the extraocular muscle was damaged but functional exercise can accelerate her recovery. There is no de nite information in the literature currently on how long it might take to restore the extraocular muscle movement to preoperative levels. This case is still being followed-up and we wish to determine whether the oblique position can recover and provide reference data for the treatment of future patients.

Conclusions
CFD is a type of disease that may signi cantly in uence one's visual function. Our case indicated that decompression may improve the visual function even the compression of optic nerve exists for a prolonged disease course. CT images demonstrated the pathognomonic ndings A: appearance of FD, a homogenous, "groundglass" lesion. Images revealed a left predominant expansion of the ethmoid and the temporal bone. B: The entire left maxillary sinus, ethmoid sinus, and bilateral frontal sinus cavities had been obliterated. C: The reconstructed CT image gave a sense of the three-dimensional shape of the lesion and showed the presence of a little stenosis of the left optic canal compared with the right.