1 Introduction

Fibrous dysplasia is a benign fibro-osseous bone lesion originating in the medullary bone and containing irregularly shaped, immature, metaplastic bone and fibroblastic tissue. In the maturation process, an isolated mass of immature trabeculae surrounded by dysplastic fibrous tissue occurs. It is continuously renewed but never properly completed. Stress misalignment and inadequate mineralization cause a significant loss in the mechanical strength of the bone, leading to the development of pain, deformity, and pathological fractures.¹

If it affects a single bone, it is called monostotic; if it involves more than one bone, it is called polyostotic. The polyostotic form is less common. Fibrous dysplasia accounts for 3 % of all bone lesions and 7 % of benign bone tumors. It is most often seen in the metaphysodiaphyseal regions of long bones, the cranium, and the pelvis, while vertebral involvement is rare.² The spine is involved in 1.4 %–5.5 % of fibrous dysplasia lesions, and the polyostotic form of fibrous dysplasia of the spine is very rare.³ However, fibrous dysplasia rarely leads to neurologic deficit and few cases have been reported with myelopathy.

The aim of this report is to present the diagnosis and treatment of polyostotic fibrous dysplasia, which acts locally aggressively, reaches large sizes, and involves the spine.

2 Case report

The patient was a 49-year-old woman who first observed a mass on her back two years ago and subsequently experienced back pain for several months. The patient reported that the pain was exacerbated by physical activity, but the primary complaint was the presence of the mass. Prior to treatment, the patient's visual analog scale (VAS) score was 5 out of 10. A history of trauma or infection was absent. Upon physical examination, a palpable mass was observed beneath the right scapula, extending to the right side of the back. A dermatological examination revealed no evidence of a skin lesion. Motor strength in the lower extremities was 3/5 according to the Medical Research Council (MRC) scale and the patient reported diffuse paresthesia. Reflex examination revealed bilateral 2+ hyperreflexia in the lower extremities. Babinski's finding was positive in both feet. She had normal bowel and bladder function.

Laboratory examination revealed an alkaline phosphatase level of 337 U/L (within the normal range of 35–105 U/L), while other tests, including a hemogram, electrolytes, C-reactive protein, and sedimentation rate, demonstrated normal results. Direct radiography of the thoracic spine revealed irregular calcific opacities in the region corresponding to the T5-6-7 spine and the right ribs at the same level. Computed tomography (CT) imaging revealed lytic lesions that were responsible for enlargement of the T6 body and its posterior elements. At the 6th rib, a mass with hyperdense signal, encased in sclerotic bones and exhibiting localized lytic areas, had advanced to the anterolateral aspect of the thorax (Fig. 1).

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Fig. 1 A. Posterior lytic areas on axial computed tomography sections. B. Three-dimensional computed tomography images demonstrate the presence of a sizable mass at the T6 vertebral level and adjacent ribs.

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Magnetic resonance imaging (MRI) revealed that the mass encased the spinal canal in the extradural region at the T6 vertebral level, resulting in a reduction in canal volume and the development of stenosis. The canal diameter was 3 mm at the narrowest point (Fig. 2). MRI and CT images were consistent with a diagnosis of fibrous dysplasia. The histopathologic evaluation of the open biopsy performed preoperatively was reported as fibrous structure accompanying an aneurysmal bone cyst.

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Fig. 2 Representation of mass within the body and posterior elements of the T6 vertebra, resulting in spinal stenosis as observed on sagittal magnetic resonance imaging.

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The patient underwent surgery with the prediagnosis of fibrous dysplasia. In the lateral decubitus position, the mass was accessed by transverse incision over the sixth rib in such a way that the previous open biopsy scar was removed in the form of a fish mouth. The mass was then separated from the surrounding tissues by sharp dissection. The sixth rib and the mass were then disarticulated from the costotransversal and sternocostal joints. The areas adherent to the parietal pleura were completely excised together with the mass, taking care to avoid creating a defect in the visceral pleura (Fig. 3).

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Fig. 3 The mass was excised via a wide resection, encompassing the sixth rib and parietal pleura, as well as the surrounding soft tissues.

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Following the hemorrhage control, a thorax tube was positioned, the fifth and seventh ribs were secured with strength sutures, and the layers were closed in an anatomically manner. Subsequently, during the same session, the patient was positioned prone. The posterior elements of the spine were accessed via a longitudinal midline incision made between the T3 and T10 vertebrae. Bilateral transpedicular screws were placed in the T3, T4, T5, T8, T9, and T10 vertebrae on both sides. The spinous processes, bilateral laminae, and facet joints of the T6 and T7 vertebrae were excised with a wide margin of tissue to include the mass. Bone structures that were causing pressure on the spinal cord were removed and width was provided in the extradural space. Subsequently, a T5 right costotransversectomy was conducted, followed by a T6 corpectomy. In pursuit of a 360-degree fusion, an expandable cage filled with autogenous grafts was positioned within the corpectomy area. The system was affixed with two rods (Fig. 4).

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Fig. 4 Postoperative direct radiograph. Stabilization with pedicle screws T3-T10 and T6 corpectomy cage.

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Histopathologic examination of the biopsy material confirmed the diagnosis of fibrous dysplasia. In addition, the biopsy material was found to contain an aneurysmal bone cyst in some places. Postoperative follow-up visits at 6th weeks, 12th weeks and 6th months were performed and the patient had no neurologic deficit and back pain. At the first postoperative year, the patient was asymptomatic, had no recurrence and was evaluated as grade I according to the modified McCormick scale.

3 Discussion

The onset of the lesion typically occurs during adolescence and young adulthood; however, it can be observed in the clinic at any age. The clinical findings are dependent on the age of the patient and the location of the lesion.¹ The monostatic form, which involves a single bone, is approximately twice as common as the polyostatic form, which involves more than one bone.⁴ The precise incidence of the monostotic form is difficult to determine because many patients are asymptomatic and are often diagnosed incidentally after radiographic evaluation for other reasons. Fibrous dysplasia represents approximately 1 % of primary bone tumors and 7 % of benign bone tumors.⁵ In the polyostotic form, the bones most commonly affected are the craniofacial bones, ribs, proximal femur, and tibia.⁶ Symptomatic patients usually present with complaints of pain and swelling. It is established that excessive osteoclastic activity, coupled with augmented bone resorption in fibrous dysplasia lesions, gives rise to pain.

The prognosis for fibrous dysplasia is typically favorable, although malignant transformation has been observed in approximately 1 % of cases. The risk of malignancy is lower in the monostotic form. In cases of McCune-Albright syndrome, the risk of malignant transformation is 4 %.⁷ The most common site of malignant transformation is craniofacial bones and most often turns into osteosarcoma. Disseminated polyostotic fibrous dysplasia has the potential to result in progressive deformities and pathological fractures. The severity of the deformation is contingent upon the location of the lesion, the age of the patient, and whether the disease is monostotic or polyostotic. Fibrous dysplasia lesions in the spine can also cause scoliosis or kyphosis.¹ Scoliosis is very rare in monostotic fibrous dysplasia.⁸ However, the prevalence of scoliosis in patients with polyostotic fibrous dysplasia has been found to be up to 40 %. Leet et al. in a study of 62 patients with polyostotic fibrous dysplasia found spinal involvement in 63 % of the patients and reported a 40 % prevalence of scoliosis in these patients and no neurologic deficit except in 2 patients.⁹ In a series of 7 cases of monostatic fibrous dysplasia of the spine with a mean follow-up of 9.8 years by Schoenfeld et al. none of the patients had neurologic deficit and scoliotic deformity. They performed curettage in two patients and symptomatic treatment and observation in the others. The size of the lesions remained constant throughout the follow-up period for all patients.¹⁰

Although neurological deficit is not expected in cases of monostotic fibrous dysplasia, single case reports have also described patients who developed spinal cord compression¹¹ or pathological fracture¹² due to the lesions. Wu et al.'s literature review and study including their own patients reported that myelopathy developed due to atlantoaxial instability, kyphosis and mass compression.¹³ Harimaya et al. retrospectively studied 10 patients with malignant tumors in the spinal column, including the posterior chest wall. All surgeries were performed with a combined anterior and posterior approach. Muscle weakness in the lower extremities was observed in two patients immediately after surgery. The cause of paralysis in both patients was unclear. However, the paralysis was temporary in both patients and completely resolved at the last follow-up.¹⁴ In our patient, preoperative motor strength in the lower extremity muscles was 3/5 according to the Medical Research Council (MRC) scale. After mass resection and spinal canal decompression, the neurological deficit was completely resolved at the 12th month follow-up.

The primary objective of surgical intervention in patients with fibrous dysplasia is to provide fixation of pathological fractures and control the size of the lesion. In the case of long bones, the surgical options are well established and include procedures such as curettage-grafting and internal fixation, which are frequently performed.¹⁵ A variety of surgical techniques have been employed for the treatment of spinal lesions, including kyphoplasty, vertebral column resection, and 360-degree fusion. Several studies have reported positive outcomes following vertebroplasty or kyphoplasty in monostatic limited lesions located in the vertebral body.¹⁶ However, this objective may not always be attainable in cases of polyostotic disease. In a case study by Joyce et al., stabilization and autologous graft fusion were performed on a patient with fibrous dysplasia lesions in the T5-7 thoracic vertebrae, without tumor resection, via a posterior approach.¹⁷ Arazi et al. resected monostatic fibrous dysplasia in the T6 thoracic vertebra en-bloc using a transthoracic approach. They utilized a costal graft and interbody cage for 360-degree fusion.¹⁸ Tezer et al. performed a costotransversectomy and corpectomy on the polyostotic lesions involving T6-8 thoracic vertebrae and achieved fusion using a titanium mesh and costal autologous graft with posterior pedicular stabilization.¹⁹

We prefer vertebroplasty instead of radical resection in lesions that are local and not disseminated, even if they are poliostatic. It offers numerous advantages over surgical resection. Cement administration has been demonstrated to reduce the risk of pathological fractures and provide pain relief through the provision of mechanical support. Nevertheless, in cases of extensive lesions that cause mass effect, as in the present case, extensive surgical resection is unavoidable. The stabilization of the spine is as crucial as the excision of the lesion in achieving successful surgical treatment outcomes in fibrous dysplasia. In lesions involving the spine, a potential for pseudoarthrosis after extensive resection will lead to repeated surgeries. Healthy fusion is essential for successful spine surgery procedures. In our patient, we performed a wide resection and spinal canal decompression by combining transthoracic and posterior approaches, aiming for 360-degree fusion using a cage filled with autograft. One year after surgery, the patient exhibited no symptoms, the neurological deficit had completely resolved, and there were no signs of instability in the fusion site.

Patient consent

Informed consent was obtained from the participant included in the study. Consent for publication was obtained for personal data included in the study.

Author list

Abdullah IYIGUN, MD: Preparation, creation and/or presentation of the published work, specifically writing the initial draft (including substantive translation).

Omer POLAT, MD: Management activities to annotate (produce metadata), scrub data and maintain research data (including software code, where it is necessary for interpreting the data itself) for initial use and later reuse.

Bekir Yavuz UCAR, Professor: Conducting a research and investigation process, specifically performing the experiments, or data/evidence collection.

Necdet SAGLAM, Professor: Management and coordination responsibility for the research activity planning and execution.

Ethical statement

All procedures performed in studies involving human participants were in accordance with the ethical standards of the Institutional Review Board and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Funding

This study was not supported by any funding.