Clinical Profile:

A 27 year old woman came with the complaints of a gradually increasing painful swelling over the right elbow since one year. The lesion is hard , well circumscribed, immobile on the  the anterior and medial aspect of right elbow joint. There are areas of discoloration over the mass.

Radiological findings:

Plain radiograph:

Sonography :

MRI :

Radiological diagnosis:

Osteogenic sarcoma

Pathological diagnosis and treatment:

The patient underwent an incisional biopsy from the elbow swelling and also an sonography guided biopsy from an axillary deposit. 

Histology showed a periosteal osteosarcoma.

She was advised  forequarter amputation and was referred to a specialist cancer center.

Timeline

Discussion

Osteosarcoma is a primary bone malignancy characterized by malignant cells of mesenchymal origin depositing immature osteoid matrix. It is one of the most common neoplasms of the musculoskeletal system, accounting for approximately one-fifth of all primary malignant bone tumours. (1)

Osteosarcoma encompasses various types of bony lesions, with the typical manifestation which is a high-grade sarcoma arise intramedullary. A few of the disease entities arise on the outer cortical surface; such lesions are termed surface osteosarcomas which are further divided into parosteal osteosarcoma, periosteal osteosarcoma, and high-grade surface osteosarcoma. Parosteal osteosarcoma represents the well-differentiated end of surface osteosarcoma, which typically consists of a slow-growing lesion that assumes a significantly better prognosis than conventional osteosarcoma. However, it rarely manifests as a dedifferentiated fashion, which is usually more abrupt and is associated with poorer prognosis. (1)

Parosteal osteosarcoma has slight female predominance and more frequently encountered in the third decade of life. Posterior aspect of distal femoral metaphysis is the most common site followed by proximal tibial and proximal humeral metaphysis. Those three locations combined account for more than 80% of all cases of parosteal osteosarcoma. The commonest presentation is pain and swelling. Systemic metastasis is rare in parosteal osteosarcomas. (1)

Histologically, parosteal osteosarcoma typically presents with irregular bony trabeculae and bland-appearing spindle cells within the fibrous stromal tissue. Markedly, atypical cells and atypical mitoses are not present. (1)

The diagnostic criteria to designate a surface osteosarcoma as parosteal osteosarcoma is that radiographically the lesion should have arisen from the surface of the bone, histologically, the tumor should be well differentiated (Grade 1 or 2); it should be characterized by well-formed osteoid within a spindle-cell stroma and medullary involvement if any should be <25% of the medullary cavity. (2)

Surface osteosarcomas can mimic benign conditions such as

osteochondroma and myositis ossificans. All clinicoradiologically doubtful lesion needs to be biopsied to confirm the diagnosis.

Cartilage cap of parosteal osteosarcoma, if present, lacks the columnar arrangement of cells and shows mild cellular atypia thus differentiating it from osteochondroma. (2)

Radiographically, it appears as a sessile, ossified, lobulated mass which attaches to the underlying bone via a broad pedicle but does not penetrate the cortex to involve the medulla. In addition, there was little or no periosteal new bone formation. A peculiar radiolucent cleft separates the majority of the ossified mass from the cortex of the femur. This cleft (1 to 3 mm in width) stops abruptly at the stalk of the tumor and has been referred to as the cleavage plane or string sign of parosteal sarcoma. This sign is present in only 30% of cases (3)

Surgery remains the treatment of choice. Wide excision with more than a 1-cm surgical margin is considered adequate, while incomplete excision almost inevitably leads to local recurrence.  In cases of marginal excision, a positive microscopic surgical margin warrants a second operation.  For recurrent disease, re-excision or amputation may provide a possible cure in cases that lack tumor dedifferentiation.  To achieve complete excision, a preoperative diagnosis and radiological evaluation of the extent of disease are required. When areas of dedifferentiation are suspected and proven by biopsy, neoadjuvant chemotherapy may improve the clinical outcome. (4)

References:

1. Prabowo Y, Kamal AF, Kodrat E, Prasetyo M, Maruanaya S, Efar TS. Parosteal Osteosarcoma: A Benign-Looking Tumour, Amenable to a Variety of Surgical Reconstruction. Int J Surg Oncol. 2020 May 28;2020:4807612. doi: 10.1155/2020/4807612. PMID: 32550023; PMCID: PMC7275216.

2. Kumar VS, Barwar N, Khan SA. Surface osteosarcomas: Diagnosis, treatment and outcome. Indian J Orthop. 2014 May;48(3):255-61. doi: 10.4103/0019-5413.132503. PMID: 24932030; PMCID: PMC4052023.

3. Yochum Rowe -Essentials of Skeletal Radiology-primary bone tumors page no. 1192.

4. Yogi Prabowo, Achmad Fauzi Kamal, Evelina Kodrat, Marcel Prasetyo, Samuel Maruanaya, Toto Suryo Efar, "Parosteal Osteosarcoma: A Benign-Looking Tumour, Amenable to a Variety of Surgical Reconstruction", International Journal of Surgical Oncology, vol. 2020, Article ID 4807612, 6 pages, 2020. https://doi.org/10.1155/2020/4807612

Acknowledgement :

We are grateful to the Department of Pathology  at our institution for providing us with an image from the histological findings as also its description.