Parosteal osteosarcoma dedifferentiating into telangiectatic osteosarcoma: importance of lytic changes and fluid cavities at imaging
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- Azura, M., Vanel, D., Alberghini, M. et al. Skeletal Radiol (2009) 38: 685. doi:10.1007/s00256-009-0672-3
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This study was performed to assess the imaging findings in cases of parosteal osteosarcoma dedifferentiated into telangiectatic osteosarcoma. Parosteal osteosarcoma is a low-grade well-differentiated malignant tumor. Dedifferentiation into a more aggressive lesion is frequent and usually visible on imaging as a central lytic area in a sclerotic mass. Only one case of differentiation into a telangiectatic osteosarcoma has been reported. As it has practical consequences, with a need for aggressive chemotherapy, we looked for this rather typical imaging pattern.
Materials and methods
Review of 199 cases of surface osteosarcomas (including 86 parosteal, of which 23 were dedifferentiated) revealed lesions suggesting a possible telangiectatic osteosarcoma on imaging examinations in five cases (cavities with fluid). Histology confirmed three cases (the two other only had hematoma inside a dedifferentiated tumor). There were three males, aged 24, 28, and 32. They had radiographs and CT, and two an MR examination.
Lesions involved the distal femur, proximal tibia, and proximal humerus. The parosteal osteosarcoma was a sclerotic, regular mass, attached to the cortex. A purely lytic mass, partially composed of fluid cavities was easily detected on CT and MR. It involved the medullary cavity twice, and remained outside the bone once. Histology confirmed the two components in each case. Two patients died of pulmonary metastases and one is alive.
Knowledge of this highly suggestive pattern should help guide the initial biopsy to diagnose the two components of the tumor, and guide aggressive treatment.
KeywordsTelangiectatic osteosarcomaParosteal osteosarcomaFluid–fluid levelsCTMRI
Parosteal osteosarcoma is a well-differentiated, low-grade variant of osteosarcoma with good survival (about 90% of patients after 5 years). In our files, it accounts for 4.8% of all osteosarcomas. Dedifferentiation is a biologic phenomenon in which a high-grade sarcoma arises on a low-grade malignancy caused by a mutation that produces a high-grade malignant clone. About 15% of parosteal osteosarcomas show foci of dedifferentiation, usually evidenced by the onset of central radiolucencies. Dedifferentiation is usually towards a high-grade spindle cell sarcoma, or a high-grade surface osteosarcoma. Only one case of differentiation into a telangiectatic osteosarcoma has been reported . We report three cases of dedifferentiated parosteal osteosarcoma with teleangiectatic osteosarcoma appearance and describe the clinicopathological and radiographic features of the tumors. Early recognition of these tumors would allow a better yield of the biopsy as well as for planning a more aggressive treatment.
Materials and methods
A systematic review of 199 patients diagnosed as surface osteosarcoma in our institution from 1916 to 2003 was performed by a radiologist and a pathologist. We identified 86 patients with parosteal osteosarcoma and among them, 23 dedifferentiated. Radiological review revealed five possible cases of telangiectatic dedifferentiation because of fluid cavities within the tumor mass on CT or MRI. Only one case had been diagnosed on the initial histological report, but the histopathology review of the five cases confirmed three dedifferentiation into a telangiectatic osteosarcoma, while the two other patients only had a hematoma inside the dedifferentiated part.
Ossified mass. lytic component
Ossified lesion. Lytic component. Minimal medullary involvement
Fluid–fluid levels in the lytic part
Wide resection, prosthesis and adjuvant chemotherapy
Died after 11 months
Pain, limited ROM
Ossified mass. Proximal lytic component
Multiple fluid cavities in the lytic part. Obvious medullary involvement in the lytic part
Neoadjuvant chemo, wide resection and prosthesis, adjuvant chemo
Died after 17 months
Ossified mass. Massive central lysis
Ossified mass. Massive central lysis. Fluid component. Poorly visible levels
Multiple fluid–fluid levels in the lytic part, much better visible than on CT
Amputation and adjuvant chemo
Alive DF for 13 years now
Parosteal osteosarcoma (POS) is a well-differentiated, low-grade variant of osteosarcoma which arises from the surface of the bone. It was first described as a new and separate entity by Geschickter and Copeland in 1951, and was named parosteal osteoma . This lesion is uncommon, and only represents 5% of all osteosarcomas. The age of presentation is between 20 to 40 years, thus more typical in adults than in teenagers, with a slight predominance in females, unlike the classic osteosarcoma . Symptoms include a slow-growing, hard mass with no or slight pain, frequently associated with limitation of joint motion due to mechanical blockage. The tumor usually involves long-bone metaphysis, mostly the posterior aspect of distal femur and proximal humerus . The classic radiological feature is a densely mineralized, amorphous mass attached to the cortex by a broad base . The lesion is hot on bone scintigraphy. Macroscopically, it presents as a hard lobulated mass attached to the underlying cortex. Peripheral cap of cartilage may be present ; therefore, the lesion can be misinterpreted as osteochondroma or heterotopic ossification. Microscopically, it consists of well-formed bony trabeculae seen in a hypocellular stroma with minimal atypia of spindle cells . The bony trabeculae may show osteoblastic rimming. The treatment is surgery with wide surgical margin. POS has good survival, however, if the lesion is not adequately resected, local recurrence is likely to develop. It can occur on the surface of bone or in the soft tissue . Okada et al. evaluated the 5-year survival of 39 patients at 91% and the 10-year survival at 80% .
Telangiectatic osteosarcoma (TOS) is a high-grade variant of osteosarcoma, with a rapidly progressive course. It was first described by Paget in 1854 . It accounts for about 9% of high-grade osteosarcoma with male sex preponderance and mostly occurs in younger age group between 10 and 20 years . Patients may complain of rapidly increasing mass which is painful with increased local temperature. Radiograph shows a purely lytic lesion with ill-defined margin and destruction of the cortex. Sometimes, this lesion can be misdiagnosed as an aneurysmal bone cyst or giant cell tumor. CT and MRI reveal multicystic lesions with fluid–fluid levels. Isotope scan will show increase uptake beyond the osteolysis but cold area at the center due to fluid collection. Angiogram shows intense vascularity, but the findings can be adverse due to massive necrosis or hemorrhage. Treatment consists of neoadjuvant chemotherapy, surgery and adjuvant chemotherapy. Mervak et al. concluded that TOS has a similar prognosis as conventional osteosarcoma .
When a parosteal osteosarcoma dedifferentiates, it means that part of the tumor has transformed into a higher-grade lesion. This dedifferentiation can occur at the time of presentation (synchronous type) or at the time of recurrence (metachronous type) . The early report by Unni et al in 1976 described seven cases with coexistent areas of high-grade malignancy in POS . The latest review series by Bertoni et al. in 2005 described 29 cases of dedifferentiated POS (dd-POS) from 120 POS. Fourteen cases dedifferentiated into an osteoblastic, ten a fibroblastic, three a giant cell-rich and two a fibroblastic high-grade osteosarcoma . Literature review revealed that telangiectatic dedifferentiation of POS was only described once, by A. Wines et al. in 2000. The case report highlighted a 28-year-old woman who was diagnosed to have telangiectatic dedifferentiation of POS on histological examination of the resected specimen . Although it seems contradictory to the definition of dedifferentiation (which involves the development of a completely different tumor), low-grade parosteal osteosarcoma is different genetically and biologically from a high-grade osteosarcoma (including telangiectatic).
In our series, the three telangiectatic dedifferentiations were synchronous, patients were males with a mean age of 28. Lesions involved long-bone metaphyses. A central radiolucency in the highly mineralized areas, indicating dedifferentiation, as well as multiple fluid–fluid levels suggesting telangiectatic dedifferentiation were found on CT and/or MR examinations. They were better seen on MR examinations. The correct histological diagnosis was made immediately only once on the histology, and corrected retrospectively in two more cases after review. Bertoni et al., in 1985, compared radiological and histological findings of 18 parosteal osteosarcoma patients with intralesional radiolucencies within the tumor. They found that the majority of high-grade dedifferentiated areas of tumors corresponded to deep radiolucencies .
The prognostic implications of intramedullary extension of parosteal osteosarcoma remains controversial. Campanacci et al., in 1984, reported that 33% of grade I POS, 65% of grade II POS, and 90% of grade III POS had medullary involvement. Their series did not have metastasis without involvement of the medullary cavity. They suggested that POS with medullary involvement is more aggressive . Other authors however concluded that medullary canal invasion cannot be considered a sign of aggressiveness. Sheth et al., in 1996, found no significant prognosis difference in medullary canal invasion . The Rizzoli group in 2005 found medullary canal invasion in 65% (19 patients) of 29 dedifferentiated POS. Eight of nine patients who died had medullary canal invasion, however, this invasion was also present in 11 patients without evidence of disease after a long follow-up .
In our center, a patient diagnosed with dedifferentiated POS, is considered as a high-grade osteosarcoma. The treatment regime will follow the osteosarcoma regimen. The adjuvant chemotherapy is given to patients with dd-POS after histopathological post-tumor resection confirmation. If the histology of dedifferentiation could be confirmed earlier during biopsy, a more aggressive treatment with neoadjuvant chemotherapy could be planned. Therefore, the ability to detect telangiectatic dedifferentiation in POS can contribute to a better yield from the biopsy and better planning from more aggressive treatment.