Polyostotic cystic fibrous dysplasia of the spine and ribs

Description

Fibrous dysplasia is a benign fibro-osseous bone lesion characterised by the substitution of the medullary component in one (mono-ostotic) or, less frequently, multiple bones (polyostotic) with immature fibro-osseous tissue. This condition is more prevalent in males. While many patients with fibrous dysplasia are asymptomatic, some may experience pain or swelling. Fibrous dysplasia represents 7% of benign bone tumours and 2.5% of all bone lesions, and it can manifest in any bone, with a higher incidence in the proximal femur, tibia, ribs and skull. Polyostotic disease often affects the craniofacial bones.¹ Spinal involvement is observed in 1.4% to 5.5% of fibrous dysplasia cases, and polyostotic fibrous dysplasia in the spine is uncommon, with fewer than 40 documented cases in the literature.^2–6 This report aims to present a case involving isolated polyostotic fibrous dysplasia in the spine and ribs with cystic components.

A man in his early 40s visited the orthopaedic clinic, reporting a chronic, progressively worsening backache. His family history was unremarkable. On examination, tenderness was noted over his dorsal spine. Laboratory tests, including blood counts, serum electrolytes, erythrocyte sedimentation rate and alkaline phosphatase, were within normal limits. A radiograph revealed multiple lytic expansile lesions in the dorsal vertebrae and adjacent ribs. Further investigation via CT scan revealed lytic expansile cystic lesions affecting the T4 to T9 vertebral bodies, their transverse processes and posterior elements. Similar lesions were observed in the ribs on both sides. Involved vertebral bodies displayed mild compression at multiple levels with slight compromise of the spinal canal and neural foramina. A mild exaggeration of thoracic kyphosis was evident, with no scoliotic deformity (figure 1 and video 1). A skeletal survey subsequent to the diagnosis did not reveal any additional lesions. Imaging differentials, in this case, were polyostotic fibrous dysplasia, expansile osteolytic metastasis, Paget’s disease and Gorham–Stout disease (vanishing bone disease).

Figure 1.

A. Frontal radiograph showing lucent expansile lesions involving multiple thoracic vertebrae and ribs. Pathological compression fractures of multiple vertebrae are seen. B. Sagittal reformatted CT of the thorax in bone window setting shows involvement of T4 to T9 vertebral bodies as well and posterior elements with multiple pathological compression fractures. Note the presence of a ground-glass matrix better visualised on CT. C. Volume rendered image of the thoracic cage shows multiple expansile lesions involving vertebral bodies and ribs on both sides. The thoracic cage is distorted due to lesions.

Video 1. CT of the thorax in a bone window setting showing multiple lytic expansile lesions involving multiple thoracic vertebrae and ribs with the presence of ground-glass matrix better visualized on CT.

bcr-2024-260222supp000.mp4 ^{(668.9KB, mp4)}

DOI: 10.1136/bcr-2024-260222.video01

A CT-guided biopsy confirmed the presence of fibrous dysplasia upon histopathological examination (figure 2). Since the patient lacked neurological symptoms and declined surgery, medical treatment with pamidronate and analgesics was initiated, and close follow-up was maintained.

Figure 2.

A. Haematoxylin and eosin-stained sections show varying proportions of fibrous and osseous woven bone deposition (H&E; x100). B. Higher magnification shows ‘Sharpey-like fibres (Growing collagen)’ without nuclear atypia between the irregular woven bone (H&E; x400).

Fibrous dysplasia is classified into two forms based on the number of affected bones: monostotic and polyostotic, with the monostotic form being more common, accounting for 75–80% of cases. The polyostotic form may be associated with syndromes such as McCune–Albright syndrome, characterised by polyostotic fibrous dysplasia, cafe-au-lait spots and endocrine dysfunction, or Mazabraud syndrome, which involves polyostotic fibrous dysplasia and soft tissue/intramuscular myxomas. No syndromic association was noted in our case. Malignant transformation is rare, occurring in only 0.5% of cases of the monostotic form, but the risk may increase to 4% in cases associated with McCune–Albright syndrome. The most common malignant tumour to occur is osteosarcoma, followed by malignant fibrous histiocytoma and chondrosarcoma. Aneurysmal bone cyst transformation in the pre-existing cystic fibrous dysplasia can add challenges to the diagnosis.^{7 8} Imaging armamentariums available for the diagnosis and follow-up of fibrous dysplasia include radiography, scintigraphy, CT, MRI and hybrid imaging like positron emission tomography (PET) combined with CT. Bone scintigraphy and PET-CT can sometimes show high uptake and avidity in cases of cystic fibrous dysplasia, and the treatment scheme should not be solely guided by them. Additional imaging is recommended for accurate staging or the development of an appropriate treatment plan.⁹

Polyostotic fibrous dysplasia limited to the spine and ribs is rare and should be recognised by radiologists to avoid misinterpretation and make a timely diagnosis to prevent further deformities and neurological compression.^2–6 The role of surgical treatment for fibrous dysplasia is controversial.¹⁰ In most cases of fibrous dysplasia involving the nonaxial skeleton, conservative treatment is recommended, even after pathological fractures. The curative potential for all fracture sites has been reported to be 94%.¹¹ Conservative treatment, particularly with polyostotic fibrous dysplasia, has also been recommended in the spine. In patients with extensive spinal involvement, like in our case, an option of surgery can be offered to the patient to prevent neural compression. When the involvement of multiple vertebral bodies necessitates resection across several segments, the process of stabilisation and fusion should be approached with care to prevent potential complications.¹² Historically, medical treatments like calcitonin, etidronate and mithramycin have been employed. The introduction of second-generation bisphosphonates has shown promise in offering non-surgical alternatives for treating individuals with fibrous dysplasia, as it is now recognised that the underlying pathology of fibrous dysplasia lesions involves excessive osteoclastic activity coupled with increased bone resorption.¹³ Denosumab has also been advocated as a potential treatment for fibrous dysplasia; however, there is limited data to support safety and efficacy.¹⁴

Patient’s perspective.

As a middle-aged man experiencing chronic and worsening back pain, I found myself at the orthopaedic clinic seeking answers and relief. The discomfort in my dorsal spine was becoming increasingly debilitating. During the examination, the tenderness over my dorsal spine raised concerns, leading to a series of laboratory tests and imaging studies. Despite the normal results from blood work and other tests, the radiograph revealed a troubling sight: multiple lytic expansile lesions in my dorsal vertebrae and adjacent ribs. This discovery prompted further investigation, including a CT scan, which provided a clearer picture of the extent of these cystic lesions affecting several levels of my spine and ribs.

The images painted a stark reality—my vertebrae were affected, showing signs of compression and compromising the spinal canal and neural foramina. The mild exaggeration of thoracic kyphosis only added to the concern, although thankfully no scoliotic deformity was detected. The confirmation of fibrous dysplasia through a CT-guided biopsy added a name to my condition but also introduced a new set of decisions to be made. Despite the absence of neurological symptoms, the option of surgery was presented to me. However, after careful consideration and discussion with my healthcare provider, I made the decision to pursue medical treatment instead. Close follow-up became essential as we embarked on this journey of managing my condition and its impact on my daily life.

Navigating this diagnosis has been daunting, but I am grateful for the support of my healthcare team as we continue to monitor and address my needs. Though the road ahead may be uncertain, I am determined to face it with resilience and optimism, taking each step forward with courage and hope for a brighter tomorrow.

Learning points.

• Fibrous dysplasia represents 7% of benign bone tumours and 2.5% of all bone lesions. Spinal involvement is observed in 1.4% to 5.5% of fibrous dysplasia cases, and polyostotic fibrous dysplasia in the spine is uncommon, with fewer than 40 documented cases in the literature.

• The occurrence of polyostotic cystic fibrous dysplasia lesions limited to the spine and ribs is rare. Radiographic features differ in spinal cases compared with extra-spinal fibrous dysplasia. CT scans may reveal typical features such as ground-glass opacities, expansile lytic lesions and sclerotic rims, while MRI findings are non-specific with variable signal characteristics. Imaging differentials in such cases can be expansile osteolytic metastasis, Paget’s disease and Gorham–Stout disease (vanishing bone disease).

• The role of surgical treatment for fibrous dysplasia is controversial, with conservative approaches generally recommended for nonaxial skeleton involvement. Conservative management, even after fractures, has shown a high curative potential. Surgery may be considered for extensive spinal involvement to prevent neural compression, but careful stabilisation and fusion are essential to avoid complications. Bisphosphonates offer non-surgical options, targeting excessive osteoclastic activity. Denosumab shows promise but lacks sufficient data on safety and efficacy.

Ethics statements

Patient consent for publication

Consent obtained directly from patient(s).