Parosteal osteosarcoma dedifferentiating into telangiectatic osteosarcoma: importance of lytic changes and fluid cavities at imaging

Dedifferentiation in bone and soft tissue sarcomas: How do we define it? What is prognostically relevant?

Dedifferentiation traditionally is defined by descriptive criteria as a tumor showing an abrupt change in histology from a conventional, classic, low-grade appearing neoplasm to a tumor that is more cellular, pleomorphic and "high grade", with grading typically being performed by subjective criteria. The dedifferentiated areas range from areas with recognizable histologic differentiation which differs from the primary tumor (such as an osteosarcoma arising from a low-grade chondrosarcoma) to areas containing sarcomas without specific histologic differentiation (such as pleomorphic or spindle cell sarcoma). Many, but not all, dedifferentiated tumors are aggressive and associated with significantly shorter survival than their conventional counterparts, even grade 3 conventional tumors. As a result, dedifferentiated tumors are generally considered to be clinically aggressive and as a result, more aggressive surgery or the addition of (neo)adjuvant chemotherapy is often considered. However, long-term (greater than 20 year) survivors are reported in the most common dedifferentiated bone and soft tissue sarcomas. Moreover, use of mitotic criterion for defining dedifferentiation in dedifferentiated liposarcoma as well as grading (by the French system) have been found to be associated with survival. This paper reviews the literature on dedifferentiated chondrosarcoma, dedifferentiated liposarcoma, dedifferentiated chordoma and dedifferentiated parosteal osteosarcoma. As a result of that review, recommendations are advocated to identify evidence-based, objective diagnostic and grading criteria for dedifferentiation that are appropriate for each tumor type. Adding such criteria will improve consistency in diagnosis worldwide, allow easier comparison of clinical research performed on dedifferentiated tumors and help communicate (to patients and clinicians) the tumors with highest risk of clinically aggressive behavior, to allow appropriate and personalized treatment planning.

Limb Salvage Surgery in a Rare Case of Recurrent Parosteal Osteosarcoma with Vascular Graft Thrombosis

Recurrent parosteal sarcomas with vascular involvement are rare and present unique challenges in their diagnosis and management. We report the case of a 21-year-old woman with parosteal osteosarcoma of the left distal femur, encasing the popliteal vessels. En bloc transarticular resection of the distal femur and popliteal vessels was performed, followed by reconstruction using a modular prosthesis and a saphenous vein autograft for both the artery and vein. On the 1st postoperative day, the patient developed an arterial thrombus requiring reintervention with a jump polytetrafluoroethylene (PTFE) graft. Histopathology confirmed parosteal osteosarcoma. After a disease-free survival of 41 months, the patient experienced local recurrence involving the PTFE graft, leading to graft compression, erosion, and subsequent thrombosis. Despite these complications, limb salvage was possible due to adequate collateral blood supply. This case highlights the feasibility of limb salvage surgery in select cases of parosteal osteosarcoma with vascular involvement.

Dedifferentiated Low-Grade Osteosarcoma, Outcome with or Without Chemotherapy: A Systematic Review

The treatment of low-grade osteosarcomas is surgical resection with wide margins. In instances of dedifferentiation, a therapeutic paradigm similar to that of conventional high-grade osteosarcoma has not been adequately evaluated in these neoplasms. The main objective of this review was to define whether the addition of chemotherapy to surgical treatment has an impact on the survival of patients with dedifferentiated low-grade osteosarcomas. Secondary objectives were to observe the degree of histological response to neoadjuvant chemotherapy and to describe the percentage of de novo dedifferentiation. A systematic search of articles including dedifferentiated low-grade osteosarcomas, published between 1980 and 2022 was carried out in the PubMed, Cochrane and Scielo databases. A qualitative synthesis of the results was performed. Twenty-three articles comprising 117 patients were included. The survival of patients treated with surgery alone and surgery with chemotherapy was not statistically significant between the two groups. A good histological response was seen in 20% of specimens treated with neoadjuvant chemotherapy. De novo dedifferentiation was seen in approximately a fifth of low-grade osteosarcomas. The evidence available suggests that the addition of chemotherapy does not have an impact on the survival of patients with low-grade dedifferentiated osteosarcomas.

Inflammation and infiltration: can the radiologist draw a line? MRI versus CT to accurately assess medullary involvement in parosteal osteosarcoma

Cancer causes inflammation as it progresses through healthy tissue. The differentiation of tumoral growth from the surrounding inflammatory change is paramount in planning surgeries seeking to preserve function. This retrospective study aims at illustrating how a careful use of imaging (computed tomography (CT)/magnetic resonance imaging (MRI)) can help to draw the line between infiltration and inflammation. Out of 72 cases of parosteal osteosarcoma in our institution we selected 22 which had pretreatment imaging, and out of those, 14 that had both MRI and CT. Using Fisher's exact test, we evaluated the performance of each technique on accurately diagnosing medullary tumor infiltration, using histological analysis as a gold standard. All cases (14/14) demonstrated medullary abnormality on MRI, but only 6/14 (42.9%) demonstrated abnormality on CT. The 8/14 cases with MRI abnormality but no CT abnormality (57.1%) showed inflammation with no tumoral cells present on histological analysis. In the cases where the two examinations showed medullary abnormality (6/14) histology demonstrated tumoral infiltration. MRI demonstrated high sensitivity and negative predictive value, but low specificity and low positive predictive value and accuracy (P=1). CT demonstrated high sensitivity, specificity, high positive and negative predictive values and accuracy (P = 0.000333). MRI is highly sensitive for the detection of medullary abnormality but lacks specificity for tumor invasion. Correlation with CT is recommended in all cases of positive MR to add specificity for tumors. The adequate use of the two imaging methods allows to differentiate between inflammatory change and tumoral infiltration in POS, relevant for surgical planning.

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.

[Parosteal low-grade osteosarcoma with focal differentiation]

This case study deals with the case of a 16-year-old male patient with a low-grade parosteal osteosarcoma of the distal femur with focal differentiation. Case history, disease course, and surgery as well as the pathological workup with final diagnosis are presented. Relevant radiologic and pathologic differential diagnoses und diagnostic pitfalls are explained in detail and discussed. Additionally, postoperative treatment options are illustrated.

Custom-made intercalary endoprosthetic reconstruction for a parosteal osteosarcoma of the femoral diaphysis: A case report

The present report describes a case of a 44-year-old female patient who presented with a palpable mass of the left thigh. A diagnosis of parosteal osteosarcoma (POS) at the femoral diaphysis was made following a diagnostic workup. Previous reports of long bone diaphyseal POS are rare. A long diaphyseal segment of the femur containing the tumor was resected along with a healthy margin of soft tissues, and the damaged bone was reconstructed with a custom-made intercalary endoprosthesis. Subsequent pathological examination of the surgical sample confirmed the diagnosis of POS. No local recurrence or distant metastasis was observed, and the patient had a positive Musculoskeletal Tumor Society score of 28/30 (93.3%) at the 28-month post-surgery follow-up. The present study describes the clinical, radiological, and pathological features of this rare type of osteosarcoma.

Telangiectatic osteosarcoma: a review of literature

Telangiectatic osteosarcoma is a rare variant of osteosarcoma and hence its occurrence, presentation, and prognosis are poorly understood. With advancements in technology and available treatment options, the scenario of its diagnosis, management, and outcome has changed. Chemotherapy with surgery was challenged previously, but has now been proved to be beneficial. We reviewed the available literature and compared results to define the characteristics of the disease, its presentation, radiographic and pathologic features, optimal treatment, and prognosis.

[Parosteal osteosarcomas: unusual findings]

OBJECTIVE

To study and evaluate the unusual findings in the natural history of parosteal osteosarcomas. Parosteal osteosarcomas are well-differentiated tumours of low grade malignancy, but may dedifferentiate into a more aggressive lesion.

MATERIAL AND METHODS

We reviewed 7 parosteal osteosarcomas treated in La Paz Hospital between 2005 and 2009 (3 were dedifferentiated parosteal osteosarcomas). The authors analysed the clinical and radiological features, histology, treatment and outcomes in this patient group.

RESULTS

There were 5 men and 2 women, with a mean age of 32.14 years, range 24-47 years. Three of seven tumours (42.8%) were dedifferentiated osteosarcomas. All three patients received chemotherapy. One patient presented with pulmonary metastases. No patient died.

CONCLUSIONS

It is important to understand that the biological phenomenon of dedifferentiation can occur in parosteal osteosarcomas. The prognosis, treatment and survival changes radically.

Parosteal osteosarcoma mimicking osteochondroma: A radio-histologic approach on two cases

BACKGROUND

Parosteal osteosarcoma is a well-differentiated variant of osteosarcoma that affects the surface of the bone. The imaging pattern is very typical. We report two cases mimicking an osteochondroma, radiologically and histologically and propose an explanation.

METHODS

The review of 86 parosteal osteosarcomas of bone revealed this atypical pattern only once. A consultation case was received in the same time, and added to ours. Patients were 28 years old and 56 years old females. Imaging studies included two radiographs, two CTscans, one MRI examination and one bone scan and the results were compared to histology.

RESULTS

On imaging, both lesions presented as ossified lobulated masses attached with a broad base to the underlying cortex. No radiolucent cleft separated the masses and the host bone and cortex continuity between the mass and the femur was seen, with medullary communication. The marrow of the mass had a different density and intensity compared to normal marrow. So, there were features of an osteochondroma (cortex and medullary continuity) and of a parosteal osteosarcoma (ossified marrow). Pathological assessment on the final specimen confirmed the presence of low-grade parosteal osteosarcomas, after an erroneous diagnosis of osteochondroma on the initial biopsy.

CONCLUSIONS

Parosteal osteosarcoma can be rarely confused with osteochondroma. A radiologic-pathologic correlation is essential. Cortex continuity is the most misleading imaging feature that may occur in parosteal osteosarcomas. A knowledge of this misleading pattern will help diagnose the lesion from the beginning.

Treatment and outcome of parosteal osteosarcoma: biological versus endoprosthetic reconstruction

BACKGROUND AND OBJECTIVES

Due to its good prognosis despite local recurrence, more and less invasive methods for surgical treatment of parosteal osteosarcoma (POS) have been described. Aim of this retrospective single-center study was to investigate differences in outcome after biological and prosthetic reconstruction.

METHODS

A total of 28 patients with POS, 14 females, 14 males, mean age of 27 years (median, 24 years; range 15-59 years), mean follow-up of 130 months (median, 104 months; range, 9-383 months), underwent wide tumor resection and prosthetic reconstruction (12 patients, 42.9%), less extensive resection and biological reconstruction (11 patients, 39.3%), rotationplasty (three patients, 10.7%), or amputation (two patients, 7.1%).

RESULTS

There were two cases of local recurrence in patients with biological reconstruction and three cases of pulmonary metastases, leading to death of disease in two. Ten-year disease-specific survival was 91.1%. There was no significant difference between prosthetic and biological reconstruction in terms of local recurrence, metastasis, or functional outcome (mean MSTS Score, 85%). There were significantly more revisions in prosthetic reconstructions.

CONCLUSIONS

Given that the resection of the tumor has clear margins, both prosthetic and biological reconstruction show similar results; prostheses allow better local tumor control, however, require more revisions over time.