A 74-year-old asymptomatic woman presented to our hospital to undergo an abdominal contrast-enhanced CT for follow-up imaging after surgical resection of an angiomyolipoma of the right kidney diagnosed with ultrasound and MRI.
As a collateral finding, CT revealed a bone lesion on the right iliac wing, next to the sacral articular surface. The lesion had a mixed density, predominantly sclerotic and determined slight bony enlargement; the cortical profile was intact, and no periosteal reaction was identified (Figures 1a and 1b). No other bone lesions were detected at CT. The patient underwent a Technetium-99m hydroxydiphosphonate bone scintigraphy, revealing a marked increased radioisotope uptake in the right sacroiliac joint. A 6-month follow-up CT was scheduled, and the patient was still asymptomatic; the CT scan revealed an increase in the size of the lesion, a larger osteolytic component with some areas of cortical disruption (Figure 2). Bone and pulmonary metastases were detected. Contrast-enhanced MR examination of the pelvis showed a bone lesion centred in the right sacroiliac joint with extra-osseous enhancing soft tissue component (Figures 3a, 3b, 3c and 3d).
Paget’s disease is the second most common chronic skeletal disorder after osteoporosis, with an incidence of 3–4% in people over 40 years of age [1]. Paget’s disease causes abnormal and excessive remodelling of bone that can lead to pathological fractures and, in rare cases, to sarcomatous degeneration [2]. The incidence of malignant transformation is about 1% [3]. The most frequent forms of malignant transformations of Paget’s disease are osteosarcoma (22–90%), fibrous histiocytoma (26%), fibrosarcoma (3–25%) and chondrosarcoma (1–15%) [3].
Paget’s disease usually affects the skull, spine, pelvis, and lower extremities. The structural changes may cause bone weakening and symptoms including pain, stiffness and reduced mobility [4]. Nevertheless, the majority of patients are asymptomatic, the diagnosis being an incidental finding on x-ray, CT or MRI [5]. Malignant transformation is more frequently observed in males between 61–70 years of age [6]. Clinically, it may be characterised by worsening of pain, pathological fractures, night sweats and weight loss; an elevation of serum alkaline phosphatase may be observed [7].
The primary radiographic feature of Paget’s disease is the widening of the bone, accompanied by other findings such as cortical thickening, osteolysis, and osteosclerosis [2]. The radiological findings of sarcomatous changes in Paget’s disease can include intensive sclerotic reaction, cortical destruction, bony spiculation, a non-healing fracture or the presence of a soft-tissue mass. CT and MRI have an important role in the diagnosis of sarcomatous transformation, allowing the identification of bony disruption as well as extra-osseous tissue.
In our patient, Paget’s disease of the bone was initially suspected based on CT and scintigraphy results. Follow-up CT and MR findings at 6-month follow-up were consistent with primary bone sarcoma, and an incisional biopsy was performed. The histological examination suggested the diagnosis of a secondary chondrosarcoma growing on abnormal bone in the setting of an underlying Paget’s disease. Due to the lack of conditions of surgery or chemotherapy, the patient underwent immunotherapy. Three-month follow-up CT examination revealed disease progression.
Malignant transformation represents a rare complication of Paget’s disease of the bone and can be suspected in patients with worsening symptoms or pathological fractures, although it can be asymptomatic. Follow-up imaging in Paget’s disease of the bone is needed, and radiologists play a pivotal role in the diagnosis and identification of complications. A definitive diagnosis of malignancy requires bone biopsy.
All patient data have been completely anonymised throughout the entire manuscript and related files.
Malignant sarcomatous transformation in monostotic Paget’s disease of bone
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Based on the provided abdomen/pelvis CT and MRI images, abnormalities are observed in the pelvis (mainly involving the iliac bone, sacrum, etc.), including disrupted bone trabecular patterns, local bone thickening and sclerosis, and focal bone destruction. On the CT scan, the affected bone shows abnormal expansion and cortical thickening, with noticeable changes in the outline of the pelvic bones. MRI sequences (including T1-weighted, T2-weighted, and contrast-enhanced sequences) indicate heterogeneous signals in the lesion area, with visible soft tissue mass signs. The T2 signal is mixed, suggesting heterogeneous soft tissue components.
Overall, there is evidence of significant bone remodeling and proliferation, coupled with focal destruction, raising the suspicion of a secondary neoplastic lesion. Taking into account the patient’s previous imaging comparisons and clinical background, there is a high index of suspicion for possible malignant transformation of Paget’s disease.
Considering the patient’s age, imaging findings, bone scan with CT and MRI correlation, and histopathological biopsy results (indicating chondrosarcoma components), the most likely diagnosis is:
“Paget’s Disease (Osteitis Deformans) with Secondary Chondrosarcoma”
Therefore, this is recognized as secondary chondrosarcoma arising from pre-existing Paget’s disease.
Based on the patient’s current condition and clinical situation, possible treatment strategies include:
As the bone structure has been significantly altered, safety and individualization are crucial when formulating rehabilitation and exercise prescriptions:
This report provides a reference analysis based on the limited current information. It is not a substitute for in-person consultations or professional medical advice. Specific treatment strategies and rehabilitation plans should be determined by specialized physicians after comprehensive evaluation of the patient’s condition.
Malignant sarcomatous transformation in monostotic Paget’s disease of bone
