A not so rare case of headache

A 40-year-old female with chronic headache for 3 years, with a progressively intense oppressive pain in the right occipital region and a history of moderate non-surgical head trauma at the age of 7 due to a car accident. She also has primary Sjogren's syndrome and severe somato-neuropathic pain syndrome. Physical examination revealed an asymmetrical non-painful increase in the occipital region on the right side, and laboratory tests were within expected parameters.

A CT scan was performed revealing expansile ground-glass opacities in the occipital, sphenoid, and clivus bones, not surpassing the cortical bone as primary findings. Subsequently, an MRI was performed, which revealed a T1 hypointense and T2 hyperintense mass with expansile behaviour, defined margins, and asymmetric cortical thinning of the occipital bone, after the application of gadolinium, the mass showed heterogeneous enhancement.

Fibrous dysplasia (FD) is caused by a postzygotic mutation of the GNAS-I gene that encodes for the osteoblast G protein, leading to dysfunction in osteoblast differentiation and increased bone resorption. [2,5]. Normal bone is replaced by fibrous connective tissue mixed with irregular trabecular bone.

Clinical manifestations depend on the location and extent of the lesions, with cranial lesions being the most common (50%). [2] Fibrous dysplasia has two subtypes: monostotic, which accounts for 70-80% of cases and is limited to a single bone, and polyostotic, which accounts for 20-30% of cases and involves multiple bones. [3,5].

CT provides information about the anatomy of lesions, allowing for the determination of disease extend [8]. Fibrous dysplasia has typical patterns of appearance on CT which include ground glass (56%), sclerotic lesions (23%), and cystic lesions (21%), this becomes more evident after contrast. The attenuation of these lesions usually ranges from 60-140 HU. CT can be helpful identifying soft tissue masses, bone destruction and malignant transformation. The differential diagnosis for fibrous dysplasia can be quite extensive due to the variety of ways it can present, but it will depend largely on the dominant pattern observed. Other characteristics include the absence of a periosteal reaction, and the presence of a "rind" sign which can help narrow the possibilities.[4]

On MRI generally, fibrous dysplasia lesions appear homogeneously low intensity on T1 and hyperintense on T2, with gadolinium application showing avid enhancement in active lesions and milder enhancement in inactive lesions [8]. MRI enhancement is influenced by bony trabeculae, cellularity, and collagen content. Bony trabeculae can decrease the T2 signal, while the presence of cystic areas can increase it. MRI is frequently used to assess nerve and soft tissue involvement, as well as malignant transformation. [4,8]

Conclusion

Fibrous dysplasia is a benign bone disorder that can lead to pathological fractures, bone deformities, and functional deterioration. Initial assessment typically includes a CT scan, which is useful for evaluating the extent of the lesion, cortical thickness, periosteal new bone formation, risk of fracture, and subtle non-displaced fractures. MRI is use to asses nerve and soft tissue involvement. Treatment options include medical and surgical management, which depend on various factors such as age of the patient, date of diagnosis, symptoms, severity, location of lesions, and complications. Radiologist are crucial in detecting bone complications associated with FD.

Written informed patient consent for publication has been obtained.