A 45-year-old man presented with gradually progressive paraparesis associated with deforming multiple painful swellings involving the chest and back.
On clinical examination multiple hard bony swellings were palpable along the ribs bilaterally in the trunk.
X-ray of the dorsolumbar spine shows expansile lytic lesions with intact sclerotic cortices involving multiple bilateral ribs. (Fig.1)
CT demonstrated lesions with ground glass matrix involving body and posterior appendages of the cervicodorsal, lumbar, sacral segments, multiple thoracic ribs and left scapula. No evidence of abnormal soft tissue mass or periosteal reaction of the involved bones were noted. (Fig. 2, 3, 4)
MRI revealed multiple expansile multiloculated solid-cystic lesions involving lower cervical and upper dorsal vertebrae, their posterior elements with extension into pre & paravertebral regions, multiple bilateral upper ribs, left scapula. The solid components were heterogeneously hyperintense in T2, hypointense on T1 WI showing heterogeneous enhancement in post-contrast study. Few areas of cystic components showed fluid signal. (Fig. 5) Prevertebral and epidural extension posteriorly causing secondary spinal canal stenosis at D2 & D3 levels causing compressive cord myelopathy. Collapse of D3 causing gibbus with kyphotic deformity of the dorsal spine at this level. (Fig. 6, 7)
Fibrous Dysplasia (FD) is a benign skeletal disorder where fibro-osseous tissue replaces the normal medullary space of bone. Classified into two types: monostotic fibrous dysplasia and polyostotic fibrous dysplasia (PFD) which is more symptomatic. The lesions are usually homolateral, monomelic in distribution. [1, 2]
Most patients present in early adolescence with variable symptoms like pain, swelling, deformity or pathological fracture, though patients with PFD usually present in their first decade. No sexual predilection has been reported. [1, 2]
Fibrous dysplasia is known in association with many disorders like McCune-Albright syndrome, hyperparathyroidism, acromegaly, diabetes mellitus, Cushing syndrome associations, soft-tissue myxomas. [1, 2]
Most common sites of involvement are femur, tibia, pelvis; while ribs, skull & upper extremity bones are involved with intermediate frequency; and rarely lumbar spine, clavicle and cervical spine. 
Isolated spinal involvement without lesions elsewhere in appendicular skeleton have been reported. 72% of lesions are localized in 1 or 2 sites of the spine, extensive spinal disease is less frequent. Strong correlation reported between spinal lesions and scoliosis. 
CT features of FD are ground glass, sclerotic, rarely radiolucent/cystic. CT is indicated for involvement of skull base, to assess cranial foraminas, spinal lesions complicated by fractures and in evaluating lesions with suspected sarcomatous transformation. 
MR findings of PFD are variable and not as characteristic as CT findings. While increased fibroblastic activity is seen as hypointense on T1&T2 sequences, the regions with cystic/necrotic degeneration, high cellularity and increased chondroid matrix cause hyperintense images on T2W with generally heterogeneous contrast enhancement. MR images in different planes help to evaluate the extent of PFD, demonstrate neurological complications but for follow up, however, their diagnostic specificity is limited by the presence of similar features in other diseases. [5, 6]
The lesions of FD show avid uptake in early perfusion and late phase on bone scintigraphy. Bone scintigraphy is useful in determining the extent of the disease and in identifying subtle lesions. 
Though incidence of malignant transformation is rare, lesions with suspicious clinical signs need to be followed-up by MR and should be compared with prior imaging. [1, 2]
Spinal involvement in fibrous dysplasia is rare; we need to look for associated findings in PFD. Although diagnosis can be made on radiography, CT/MRI have specific indications and are complementary for preoperative evaluation.
Differential Diagnosis List
Polyostotic fibrous dysplasia
Polyostotic fibrous dysplasia