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Background
Depending on the number of bone involved, fibrous dysplasia (FD) is generally classified as monostotic FD (MFD; single bone affected) and polyostotic FD (PFD; multiple bones affected). Although craniofacial bone involvement can occur in both types of FD, polyostotic variant is more prevalent. 1 The most affected bones in decreasing order for MFD are cranial bones, facial bones, rib, femur, tibia, humerus and those in PFD are femur, tibia, cranial bones, facial bones, pelvis, rib, upper extremities and clavicle. Only 1.4-5.5% of all FD lesions reported spinal involvement of which, lumbar spine is the most commonly affected followed by thoracic, sacral and cervical. 2 3 Based on the diverse histopathological features in correlation with the clinical occurrence and event of prenatal genetic mutation, FD can be classified into three types: Chinese letter pattern, pagetoid pattern and hypercellular pattern. 4
To the best of our knowledge, on rigorous PubMed/ medline search, the present case is the first of its kind to report occurrence of sternum, rib and cervical vertebra involvement in histopathological pagetoid variant of polyostotic FD.
Case presentation
A 30-year-old woman presented with a 1-year history of swelling under her right eye that had gradually increased in size. On extraoral examination, a large, ill-defined swelling measuring approximately 8x6 cm was noted on the right side of face extending anteroposteriorly from preauricular region to nasolabial fold and frontonasal region and superoinferiorly from zygoma to body of mandible ( figure 1 ), causing ipsilateral proptosis ( figure 2 ) and contralateral deviation of nose. Functional deformity was absent. On intraoral examination, the swelling caused obliteration of the right maxillary and mandibular buccal vestibule in relation to 14-17 and 44-47 regions.
Investigations
Radiologically, the posteroanterior view and lateral view of skull revealed expansile lytic lesions involving right frontal, parietal, temporal, zygomatic, maxillary and mandibular bones. The lesions show ground glass attenuation in diploic spaces of calvarium; medulla could not be differentiated from the cortex ( figures 3 and 4 ). CT of the head and neck revealed diffuse ill-defined expansile ground glass lesions in right frontotemporoparieto-occipital calvarium, right sphenoid, base of skull, petrous part of right temporal, right medial wall of ethmoid bone, right lateral wall of orbit, right zygomatic process, right maxilla, right mandible and vomer...