Dedifferentiated Primary Parosteal Osteosarcoma of the Temporal Bone in a 19-Year-Old Patient: A Case Report.

Osteosarcoma is the most common primary malignant tumor affecting the bone but is a rare occurrence in the head and neck region. Complete surgical resection with wide surgical margins is currently the main treatment strategy for osteosarcoma but can be hard to achieve due to the complex anatomy of the head and neck. We report the first case of primary high-grade dedifferentiated parosteal osteosarcoma arising from the temporal bone in published literature. The 19-year-old patient presented with a left retroauricular lesion measuring 3 cm in diameter. Radiographic imaging and biopsy suggested the diagnosis of intermediate-grade chondrosarcoma, but definitive histopathology confirmed a diagnosis of dedifferentiated parosteal osteosarcoma. The tumor was resected with wide margins, removing the underlying temporal bone, periosteum and overlying soft tissue through a lateral temporal bone resection. The middle ear was reconstructed with cartilage grafting, and the dura of the posterior and middle cranial fossa was covered using temporal fascia grafts and local transpositional flaps. The patient is recurrence free 10 months after treatment. This report was assembled following CARE [The CARE guidelines (for Case Reports)] guidelines and describes clinical, histological, and radiological manifestations of our patient's rare clinical entity and may provide more data in treating patients with osteosarcoma affecting the anatomically complex head-and-neck region.

Periosteal chondrosarcoma: an unusual juxtacortical sarcoma.

Periosteal chondrosarcoma is a rare tumor. It can be difficult to diagnose radiographically and pathologically and can be confused with periosteal osteosarcoma; however, the treatment of these two lesions is quite different. Increased awareness of imaging features of this lesion, particularly those that can help differentiate it from other surface-based tumors, can help one recognize this entity. We report the case of a periosteal chondrosarcoma in a young woman, highlighting the diagnostic imaging features of this disease, and her treatment with a joint-sparing geometric resection of the distal femur, using patient-specific 3D-printed cutting guides and matched allograft reconstruction.

Does the adherence of distal femur parosteal osteosarcoma to the neurovascular bundle increase the rate of local recurrences?

BACKGROUND: Proximity of tumor to the neurovascular bundle (NVB) makes achieving a wide margin difficult. In low-grade parosteal osteosarcoma (POS), it is not clear whether adherence of tumor to NVB increases the rate of local recurrence (LR). In this study, we evaluated whether tumor adherence to the NVB increases the risk of LR in low-grade POS of the distal femur? HYPOTHESIS: We hypothesized that if the thin neurovascular barrier (the adventitia of the vessels and the epineurium of the nerve) prevents tumor penetration, the rate of LR should be comparable between the lesions with and without a continuous layer of healthy fatty tissue between the tumor and NVB. MATERIALS AND METHODS: In a retrospective survey, 30 patients with low-grade POS of the posterior aspect of the distal femur were evaluated for the proximity of mass to NVB. Based on the proximal to distal T1 axial MRI sections, the tumors were divided into two groups including the tumors with an uninterrupted (group A) and interrupted (group B) rim of fatty tissue between the mass and NVB. The rate of LR was compared between the two study groups. The concordance of MRI in detecting NVB adherence was checked with pathology specimen. RESULTS: Using MRI, we identified 16 cases in group A and 14 cases in group B. The MRI status of fatty rim was concordant with pathology specimen in 96.4% of cases. The mean follow-up period of the two groups was not statistically different (117±27.6 vs. 105.8±29.4 months, respectively, p=0.29). The other baseline characteristics of the two groups were statistically comparable, as well. The rate of LR was 12.5% (2 out of 16 patients) in group A and 14.3% (2 out of 14 patients) in group B (95% CI: 0.142-9.586, p=0.87). The 10-year recurrence-free survival was 87.5% for group A and 85.7% for group B (p=0.9). DISCUSSION: The absence of a continuous rim of fatty tissue between the tumor and NVB in MRI does not increase the risk of LR in low-grade POS of the distal femur. LEVEL OF EVIDENCE: IV.

Parosteal osteosarcoma of the thumb: A case report and literature review.

Parosteal osteosarcoma (PO) is a rare malignant tumor arising from the surface of the bone. Locations in the hand are even more exceptional. This low-grade osteosarcoma shows non-specific clinical and radiological presentation, making diagnosis challenging. Moreover, histologic examination is extremely difficult and can easily lead to misdiagnosis. We report the case of a 21-year-old woman who presented PO of the right thumb, initially diagnosed as a "benign exostosis" 9 years previously. En-bloc resection followed by reconstruction using a free corticocancellous iliac crest autograft provided good esthetic and functional outcome. No recurrence occurred at 2 years' follow-up. Our literature review confirmed the rarity of PO of the hand, with only 8 cases reported in the past 60 years. Amputation was the main treatment, but some authors reported limb-sparing surgery. The present result and those in the literature review support conservative surgery when feasible, with little recurrence and better functional and esthetic results. These rare tumors should not be misdiagnosed, and should be treated in specialized centers to optimize outcome.

Parosteal osteosarcoma of the mandible in a pediatric patient.

Gnathic osteosarcoma is a rare malignant mesenchymal neoplasm showing evidence of osteoid matrix formation. Clinical behaviour and radiological appearances overlap with benign osseous lesions and are prone to misdiagnosis. Early diagnosis of osteosarcoma plays a crucial role in the treatment plan and prognosis. Herein a rare case of parosteal osteosarcoma of fibroblastic histologic subtype affecting the angle of the mandible in a 12-year-old female is presented.

Parosteal Osteosarcoma: A Benign-Looking Tumour, Amenable to a Variety of Surgical Reconstruction.

Osteosarcoma arising from cortical surface is classified into parosteal, periosteal and high-grade surface osteosarcoma. Along the spectrum, parosteal osteosarcoma occupies the well-differentiated end. It is a relatively rare disease entity, comprised only 4% of all osteosarcomas and barely reported in the literature. The objective of this study is to describe cases of parosteal osteosarcoma as well as a variety of treatment options amenable to such entity. Six cases of parosteal osteosarcoma were identified based on histopathological reports in a tertiary referral hospital in Jakarta, Indonesia between January 2001 and December 2019. The mean age was 29.8 years old; four of them (66.7%) were male. Distal end of femur was the most commonly involved bone (five cases, 83.3%). The patients were treated with wide excision followed by several different reconstruction methods: replacement with endoprosthesis, extracorporeal irradiation, knee arthrodesis, or prophylactic fixation. One of our patients presented with dedifferentiated component, and therefore was treated by limb ablation. While two cases died of pulmonary metastasis, other patients reported fair to excellent functional outcome.

Gene amplification and tumor grading in parosteal osteosarcoma.

BACKGROUND: Parosteal osteosarcoma (POS) is a unique low grade osteosarcoma. Two separate oncogenes, MDM2 and CDK4, are specifically amplified in POS. Its clinical behavior is usually indolent. In some occasions, it may progress to high grade and become fatal. Malignant transformation with high grade differentiation is the most reliable indicator to predict its aggressiveness and metastatic potential. This study is to discover the relationship between gene amplification and grading. METHODS: Retrospective analysis of MDM2/CDK4 expression/amplification using immunostaining, multiplex quantitative polymerase chain reaction (MQPCR) and fluorescence in situ hybridization (FISH) were studied on 14 patients with recurrent POS. RESULTS: Forty tumor specimens in formalin-fixed paraffin-embedded blocks from 14 patients of POS were included in this study. Twenty-seven tumors are low-grade, 13 are high-grade. All POS showed increased expression of both MDM2 and CDK4 proteins, but not those from conventional osteosarcoma. Except some tumors were non-informative (poor DNA quality), the rest of POS had a marked increase of MDM2 and CDK4 genes copies by MQPCR, and confirmed by MDM2 FISH. Moreover, the folds of amplification increase as tumors progress. And, the amplification folds in high-grade POS are consistently higher than those of conventional ones. CONCLUSION: FISH and MQPCR are both useful assays for estimating oncogene amplification status in bone tumors. Amplification levels of MDM2 and CDK4 are related to tumor grading and progression. Molecular determination of gene amplification status can be a reliable alternative for predicting clinical behavior of POS at small biopsies.

Parosteal osteosarcoma: a monocentric retrospective analysis of 195 patients.

Parosteal osteosarcoma is a low-grade malignant bone tumor that can undergo dedifferentiation. The aim of this study was to analyze clinicopathologic features associated with clinical outcome in a large cohort of patients. Patients consecutively treated for parosteal osteosarcoma at Rizzoli Orthopedic Institute from 1900 to 2018 were reviewed and analyzed. Clincopathologic data of 195 patients with parosteal osteosarcoma were analyzed. Age at diagnosis ranged from 9 to 75 years (median 31). Median follow-up time was 150 months (range, 3-720). The most common tumor locations were femur (61.5%), humerus (15.9%) and tibia (12.8%). Wide surgical margins were achieved in 125 (64.1%) patients. Medullary involvement was present in 69 (35.4%) cases. Dedifferentiation occurred in 48 (24.6%) patients. Forty-five patients developed recurrence (23.1%; median time to recurrence of 36 months). At last follow-up, 155 (79.5%) patients were alive and without evidence of disease, 8 (4.1%) were alive with active disease, 23 (11.8%) died from disease, and 9 (4.6%) from unrelated causes. Patients with dedifferentiated parosteal osteosarcoma had worse 5-year (65% versus 96%) and 10-year survival (60% versus 96%) when compared to conventional tumors (P < .001). Wide surgical margins had positive impact on both disease-free (P < .001) and overall survival (P = .036). Medullary involvement, age at presentation and tumor size had no impact on survival. Dedifferentiation is the most important factor that negatively impacts clinical outcome. Surgical aim is to ensure radical removal with wide surgical margins to improve disease-free survival.

A rare rib lesion due to parosteal osteosarcoma: a case report.

INTRODUCTION: Masses which develop on the surface of the rib bones are rare. The differential diagnosis includes benign and malignant lesions. CASE PRESENTATION: A 23-year-old European woman presented at an out-patient clinic with a 9-month history of a painless swelling on the right posterolateral side of her chest wall. The case reported here is of a very rarely seen parosteal osteosarcoma of the rib that was treated with wide resection and chest wall reconstruction. There was no evidence of local recurrence or distal metastasis after a 1-year follow-up. CONCLUSION: Parosteal osteosarcoma is a locally aggressive malignant tumor, and resection with a wide margin is the most appropriate treatment. Correct diagnosis of parosteal osteosarcoma is challenging for an orthopedic surgeon. Although rare, in the differential diagnosis of lesions located on the ribs, parosteal osteosarcoma should be considered and a systematic diagnostic approach should be taken.

Can imaging distinguish between low-grade and dedifferentiated parosteal osteosarcoma?

BACKGROUND: Most instances of the parosteal osteosarcoma (OGS) are low-grade tumors. However, some parosteal OGSs undergo dedifferentiated transformation. Dedifferentiated parosteal OGS can cause distant metastasis and poor survival, and preoperative chemotherapy may be warranted. This study provides imaging clues for dedifferentiated parosteal OGS before treatment. METHODS: The study retrospectively enrolled 23 patients with histologically proven parosteal OGS, including 69.6% (n = 16) low-grade and 30.4% (n = 7) dedifferentiated types. Preoperative images including radiography and magnetic resonance imaging were reviewed. The following imaging parameters and clinical outcomes were evaluated: 1) average age; 2) sex; 3) tumor size; 4) presence of string sign; 5) necrosis; 6) hemorrhage; 7) solid soft tissue component; 8) perforating vessels; 9) ossification grade; 10) marginal ossification; 11) periosteal reaction; 12) sunburst reaction; 13) bone marrow edema; 14) bone marrow invasion; 15) perifocal soft tissue edema; 16) adjacent joint involvement; 17) adjacent neurovascular bundle compression; 18) regional lymph node; 19) bone metastasis; 20) preoperative lung metastasis; 21) follow-up lung metastasis; and 22) recurrence. RESULTS: The average maximal tumor sizes were 7.1 cm and 10.9 cm in low-grade and dedifferentiated types, respectively (p = 0.033). Sunburst periosteal reaction was visualized in two cases of low-grade type (12.5%) and four cases of the dedifferentiated type (57.1%) (p = 0.025) of parosteal OGS. None of our studied cases revealed preoperative lung metastasis. In the follow-up chest computed tomography, lung metastasis was noted in two cases of conventional type (14.2%), and four cases of dedifferentiated type (57.1%) (p = 0.040) of parosteal OGS. In receiver operating characteristic (ROC) curve analysis, the average tumor size and sunburst periosteal reaction showed good specificity (AUC = 0.070 and 0.072, respectively). CONCLUSION: Compared with low-grade types, dedifferentiated parosteal OGS exhibits a considerably larger tumor size, more sunburst periosteal reaction, and a more frequent development of lung metastasis in the disease course. Tumor size and sunburst periosteal reaction are the most crucial imaging diagnostic factors.

On the importance of considering disease subtypes: Earliest detection of a parosteal osteosarcoma? Differential diagnosis of an osteosarcoma in an Anglo-Saxon female.

A case of potentially dedifferentiated parosteal osteosarcoma was found in the proximal humerus of an adult female buried in the late Anglo-Saxon cemetery of Cherry Hinton, Cambridgeshire, UK. Key features include a large, dense, lobulated mass attached to the medial metaphysis of the proximal humerus by a broad-based attachment, accompanied by cortical destruction and widespread spiculated periosteal reaction. Radiographic images confirm medullary involvement, lack of continuity between the cortex and external mass, a radiolucent cleavage plane and possible radiolucent zones within the bony masses. Differential diagnoses considered include osteochondroma, myositis ossificans, fracture callus, as well as the primary malignancies of osteosarcoma and chondrosarcoma, and their various subtypes. The macroscopic and radiographic analysis of the tumor is described and discussed within clinical and paleopathological contexts. One of only 19 uncontested examples of osteosarcoma from past human populations, most of which remain unconfirmed, this case represents what we believe to be the earliest, and probably singular, bioarcheological example of parosteal osteosarcoma in human history.

A Pediatric Case of Metastatic Conventional Parosteal Osteosarcoma Treated With Multidrug Chemotherapy.

Parosteal osteosarcoma (POS) is conventionally a low-grade sarcoma with limited metastatic potential; however, the tumor occasionally transforms into a high-grade dedifferentiated POS, which commonly metastasizes to distant organs. The present report describes a rare pediatric case of conventional POS with no dedifferentiated component yet had multiple pulmonary metastases at initial diagnosis. Following limb-sparing surgery and osteosarcoma-oriented neoadjuvant chemotherapy, the patient received total resection of pulmonary metastases. Despite no treatment for pulmonary recurrence 1 year after adjuvant chemotherapy, the patient is alive with stable disease 4 years and 6 months after the initial diagnosis.

Características clínicas e epidemiológicas do paciente adolescente portador de osteossarcoma / Clinical and epidemiological characteristics of adolescent patients with osteosarcoma

O Osteossarcoma (OS) é uma neoplasia maligna que afeta o tecido ósseo, sem causa aparente, acomete mais o esqueleto apendicular, principalmente fêmur e tíbia de crianças e adolescentes. O tratamento consta de cirurgias de ressecção do tumor ou amputação de membros associados à quimioterapia. Quanto mais cedo se descobrir e tratar o OS, e quanto menor for a sua extensão melhor o prognóstico. Objetivo: Conhecer as características clínicas e epidemiológicas do paciente adolescente portador de OS atendido no Hospital do Câncer do Ceará (HCC) no Município de Fortaleza. Para isso foi investigado dados clínicos e epidemiológicos referentes aos pacientes adolescentes (de 10 à 19 anos) portadores de OS. Método: Realizou-se um estudo documental retrospectivo através dos prontuários dos pacientes atendidos nesse hospital no período de Janeiro de 2006 a Dezembro de 2007. Os dados foram coletados através de uma ficha semi-estruturada que constava de questões referentes às características clínicas e epidemiológicas dos pacientes, além dos dados de identificação. Foram selecionados 29 prontuários, sendo utilizados 26 para análise, pois 03 estavam incompletos por abandono de tratamento ou transferência hospitalar. Resultados: O OS foi mais frequente em pacientes do sexo masculino (57,7%), com idade entre 10 e 15 anos (73,1%), de raça afro-descendente (50%) e que residiam no interior (73,1%); 30,8% apresentavam história de câncer na família. O sintoma em comum detectado na queixa principal foi a dor (24 pacientes), seguida do aumento do volume local (20) e trauma prévio (08). O fêmur foi acometido em 65,4% dos casos, com ocorrência de metástase (76,9%), quase sempre ao diagnóstico e sua maioria (15 pacientes) para o pulmão. O tratamento consistia em quimioterapia (96,2%) associada a ressecção cirúrgica (69,2%) e amputação (73,1%) ou substituição por endoprótese. Outras especialidades como a fisioterapia foi prescrita em 42,3% dos casos tendo início no período do pós-operatório (23,1%) e geralmente para tratar as complicações. O paciente portador de OS se caracteriza por ser homem, afro-descendente, proveniente do interior e com antecedentes familiares de câncer. Conclusão: É necessário e importante conhecer as características clínicas e epidemiológicas do paciente portador de OS, redirecionando o olhar dos profissionais de saúde para a importância da inclusão de uma equipe multidisciplinar ao diagnóstico.

Osteosarcoma (OS) is a malignant neoplasia that affects the bone tissue with no known cause. It most commonly affects the appendicular skeleton, mainly the femur and tibia bones, in children and adolescents. The surgery treatment consists of a resection of the tumor or amputation of the affected limb, associated with chemotherapy. The earlier it is diagnosed and treated, and the smaller it is, the better the prognosis will be. Objective: The main objective of this study was to present the clinical characteristics and epidemiology of adolescent patients from the Ceará Cancer Hospital (HCC) in the city of Fortaleza. Clinical and epidemiologic data about these patients, who ranged from the age of 10 to 19 years old, was investigated in order to fulfill our objectives with this study. Method: A retrospective cohort study was developed gathering information from patients' charts from the above-mentioned hospital from the period of January 2006 to December 2007. The data was collected through a semi-structured form that consisted of questions that appraised both the clinical and epidemiological characteristics of the patients, as well as the demographic data. After selecting 29 cases, only 26 were used for the analysis due to either incomplete information, abandonment of treatment, or hospital transference. Results: Our results show that Osteosarcoma was found to be more frequent in male patients (57.7%), in patients between 10 and 15 years old (73.1%), in afro-descendant patients (50%), and in patients that came from more rural areas (73.1%). This study also shows that 30.8% of the patients presented a family history of cancer. The symptom that these patients seemed to have in common was pain (24 patients), followed by an increase of local volume (20 patients), and previous trauma (8 patients). The femur bone was affected in 65.4% of the cases, with occurrence of metastasis (76.9%), almost always during the diagnosis and with the majority (15 patients) to the lungs. The treatment consisted of chemotherapy (96.2%) associated with the surgical resection (69.2%) and amputation (73.1%) or limb replacement. Other treatments such as Physical Therapy were prescribed in 42.3% of the cases, mostly during post-surgery (23.1%), and generally just to treat the complications. Conclusion: This study suggests that the common profile of a patient with Osteosarcoma is male, afro-descendant, coming from the more rural areas and presenting a family history of cancer. In conclusion, this study suggests the importance of knowledge about both clinical and epidemiological characteristics of Osteosarcoma patients, so that there is more regard from health professionals concerning multidisciplinary teamwork at the time of the diagnosis.

Análise molecular dos genes HRPT2 e ciclina D1 na displasia fibrosa, no fibroma ossificante e no osteossarcoma dos maxilares / HRPT2 and Cyclin D1 molecular investigation in fibrous dysplasia, ossifying fibroma and osteosarcoma of the jaws

A displasia fibrosa (DF), o fibroma ossificante (FO) e o osteossarcoma (OS) são considerados lesões ósseo-relacionadas, que possuem uma patogênese incerta. O gene HRPT2 codifica uma proteína de 531 aminoácidos denominada parafibromina. Recentemente, foram descritas mutações no gene supressor de tumor HRPT2 em FO. Neste estudo, pela primeira vez, foi levantada a hipótese se estas alterações também não poderiam participar da patogênese da DF e do OS, além fod FO. Em amostras de lesões ósseo-relacionadas, foram investigadas alterações no gene HRPT2/parafibromina em nével de DNA ( por meio de análise da perda de heterozigosidade - LOH), do trancrito mRNA (por meio do RT-PCR, do sequenciamentodireto e PCR quantitativo em tempo real) e da proteína (por meio de imunoistoquímica)...

Local recurrence of a parosteal osteosarcoma 21 years after incomplete resection.

Parosteal osteosarcoma (POS) is the most common form of surface osteosarcoma. Its symptoms are insidious and its duration prior to diagnosis is considerably longer than that of other types of osteosarcoma. We report a case of POS with a growing mass but no evidence of metastasis. This tumor, which was diagnosed as calcified hematoma with benign characteristics, was incompletely resected in our hospital 21 years before the diagnosis of recurrence. The patient underwent a wide en bloc resection in our hospital and was free of symptoms, with no signs of tumor recurrence or metastasis during a 53-month follow-up.

Peripheral ossifying fibroma and juxtacortical chondrosarcoma in cynomolgus monkeys (Macaca fascicularis).

Literature on spontaneous primary bone tumors in nonhuman primates is sparse. This case report describes 2 different neoplastic bone lesions in 2 adult cynomolgus monkeys (Macaca fascicularis), including macroscopic, radiographic, histologic, and immunohistochemical findings. In one monkey, a firm mass located at the palatogingival junction of the left rostral maxilla was confirmed to be a peripheral ossifying fibroma in light of its histologic and immunohistochemical characteristics. In another monkey, a lobulated tumor at the right distal femur that radiographically showed moderate radiopacity with splotchy areas of mineralization was confirmed to be a juxtacortical chondrosarcoma on histologic examination. The 2 neoplastic bone lesions revealed rare histologic and immunohistochemical characteristics and contribute to the known tumor spectrum of cynomolgus monkeys.

MRI findings in parosteal osteosarcoma: correlation with histopathology.

PURPOSE: To assess the role of magnetic resonance imaging (MRI), particularly signal intensity changes, in predicting the dedifferentiation of parosteal osteosarcoma, and to evaluate other factors that may affect grading on MRI. MATERIALS AND METHODS: MRI of 12 patients with parosteal osteosarcoma diagnosed on plain radiography were reviewed with regard to size, location, extent, soft tissue component, intramedullary invasion, and signal characteristics. The findings are correlated with histopathologic results. RESULTS: By histopathological examination there were 6 Grade I, 3 Grade II, and 3 Grade III tumors. Average size was 11 cm. All cases had a soft tissue component. Intramedullary extension was evident in 3/6 of the Grade I cases, 2/3 of the Grade II cases, and all (3/3) of the Grade III cases. T1-weighted images revealed lesions of marked hypointensity. Signal intensity on T2-weighted images varied with the presence of necrosis and hemorrhage in relation to size, regardless of the grade of the tumor. Contrast-enhanced images revealed enhancement of the solid components; no enhancement was observed in the necrotic or hemorrhagic parts. CONCLUSION: High and heterogeneous signal on T2-weighted images of Grade I, II, and III tumors is not specific for the dedifferentiated component, due to hemorrhage and necrosis in large masses. Therefore, high signal intensity on T2-weighted images is not always a reliable way to predict the grade of the tumor. Contrast enhanced T1-weighted images can be valuable to show the solid component in the heterogeneous areas on T2-weighted images, and can be useful in guiding the biopsy.

Parosteal osteosarcoma of the orbit.

A 60-year-old woman was referred to Bristol Eye Hospital because of a progressive, painless, right proptosis. CT revealed a well-defined, hyperdense lesion adjacent to the lateral orbital wall. A marginal excision was performed. The mass was stony-hard, lobulated, and encapsulated. Histopathologic findings were consistent with a low-grade parosteal osteosarcoma. Parosteal osteosarcoma is a rare osteogenic tumor that usually affects the long bones. It represents a malignant, though well differentiated, tumor that has a relatively good prognosis after a wide excision. However, local recurrences are not rare and have been associated with dedifferentiation. The latter affects the prognosis adversely and, thus, regular follow-ups are strongly suggested after the initial tumor excision. In the present case, no further treatment was administered and the patient was reported disease free 26 months after surgery.

Dedifferentiated parosteal osteosarcoma with giant cell tumor component.

Dedifferentiated parosteal osteosarcoma is characterized histologically by the admixture of low-grade fibroblastic osteosarcoma and a high-grade component typically resembling conventional osteosarcoma or malignant fibrous histiocytoma. We report an unusual distal femoral dedifferentiated parosteal osteosarcoma in which the dedifferentiated component resembled a giant cell tumor of bone. This phenotype is rarely described in the dedifferentiated component of a dedifferentiated parosteal osteosarcoma. The clinical, radiographic, and pathologic features of this unusual tumor are described to further expand the histologic spectrum of dedifferentiated parosteal osteosarcoma.