A 72-year-old man with a history of right lower limb deformity since the age of six years presented to the department due to increasing pelvic pains over the past two weeks. Physical examination revealed a shortened right lower limb with palpable right pubic mass upon which he was sent for imaging.
The CT scan of the Chest, abdomen, and pelvis done for tumor screening showed bone expansion with cystic changes and ground glass matrix in the pelvic girdle (Figure 1), proximal right femur, humerus, and scapula with coarse trabeculation (Figure 2). The right femur demonstrated the shepherd crook’s deformity (Figure 3). Also noted was the focal ground-glass area with cystic changes in the left scapula and humerus. An ill-defined heterogeneously enhancing soft tissue density mass was seen arising from the right superior pubic ramus with cortical destruction [Lodwick-Madewell classification 3B] (Figure 4).
The biopsy of resected neoplasm showed areas of diffuse population of pleomorphic cells with numerous mitosis and foci of necrosis suggestive of high-grade pleomorphic malignancy (Figure 5). Based on Immunohistochemistry (IHC), Vimentin turned out to be positive, while Desmin, CD34, S-100, HMB45, and CD 45 were all negative.
Fibrous dysplasia (FD) is a benign fibro-osseous lesion that typically occurs within the medullary space of bones in both pediatric and adult patients [1]. FD mostly occurs as a single lesion (monostotic) that is usually diagnosed in the first three decades of life and, less often multiple sites (polyostotic). Polyostotic FD is typically diagnosed in the first ten years of life and tends to involve the skeleton diffusely or on one side of the body. In both forms of FD, the long bones mainly the proximal femur and tibia, jaw, skull, and ribs are the most commonly affected sites [1]. Many patients of FD are asymptomatic, while others can present with pain, deformity, asymmetry, or pathologic fracture.
FD lesions are typically intramedullary, well-circumscribed, and often expansile lesions of variable densities. FD shows varying degrees of ground-glass density and may appear almost entirely lucent to almost completely sclerotic [2]. In the long bones, lesions are usually diaphyseal or meta-diaphyseal and rarely involve the epiphysis. They may be eccentric or centrally located. Although endosteal scalloping and cortical thinning can be seen, the outer cortex remains smooth and intact in benign diseases [2]. Expansile remodelling can cause “bulging or undulating” contours [3]. Because FD weakens the bone, weight-bearing bones can become deformed and bowed, resulting in the “shepherd’s crook” deformity. Although there have been numerous case reports, as well as a few small series describing malignant degeneration of FD, many cases are from the era before cross-sectional imaging was routinely available and descriptions of the imaging findings remain limited [4, 5, 6, 7,8].
Microscopically, FD is composed of characteristic curvilinear trabeculae of woven bone in C, S, or Y shapes and bland fibroblastic cells. Histologically, the malignant transformation of FD most commonly occurs as high-grade osteosarcoma, chondrosarcoma, and fibrosarcoma [4]. Vimentin expression may occur in pleomorphic sarcoma and osteosarcoma [9].
A detailed review of the clinical information revealed a history of polyostotic FD. Imaging findings with pathological correlation were compatible with the malignant transformation of FD.
Even though the malignant transformation of the FD is rare, clinical symptoms such as increasing pain with radiological findings such as bony destruction with or without soft tissue mass should raise the suspicion for malignant transformation.
This case underlines the importance of correlation of clinical, radiologic, and pathological findings.
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High-grade pleomorphic sarcoma
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According to the provided CT images and clinical information, there are significant abnormalities in the bilateral pelvic bones. The right iliac bone and pubic region show uneven density, characterized by varying degrees of “ground-glass” changes and bone expansion. Localized bone destruction is observed, accompanied by the formation of a soft tissue mass. The proximal right femur exhibits abnormal morphology, cortical thinning, and a distinctly deformed appearance consistent with the previously documented “shepherd’s crook” deformity. Overall, the imaging findings are consistent with localized erosion or malignant transformation on the basis of fibrous dysplasia (fibrous bone lesion).
Considering the patient’s history (multiple fibrous bone lesions diagnosed previously), clinical presentation (recent worsening pain and a palpable mass), imaging findings (“ground-glass” matrix, bone expansion with signs of erosion and soft tissue mass), and pathological examination suggesting malignancy, the most likely diagnosis is malignant transformation of fibrous dysplasia (commonly manifesting as osteosarcoma, chondrosarcoma, or fibrosarcoma).
The specific subtype of malignancy can be further confirmed using immunohistochemical staining or more detailed pathological evaluation following surgical resection. Further histological and molecular tests can help determine the precise subtype if needed.
Given the patient’s history of skeletal deformities and the current suspected malignant bone tumor transformation, a personalized rehabilitation program focusing on safety is essential:
Example of FITT-VP Principle:
Before undertaking any form of exercise, this patient should consult with the attending physician or rehabilitation specialist to develop an individualized plan and avoid fractures or risk of further tumor spread due to inappropriate or excessive exercise.
This report is a reference analysis based on the existing medical history and imaging data and cannot replace face-to-face consultation or the actual diagnosis and treatment advice of professional physicians. All diagnostic and rehabilitation measures should be carried out under the guidance and supervision of qualified medical professionals. If you have any questions or changes in symptoms, please seek medical attention promptly.
High-grade pleomorphic sarcoma
