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Parosteal osteosarcoma

Summary

Parosteal osteosarcoma is the most common form of surface osteosarcoma.

This tumor mostly occurs in young adults.
This slow growing mass presents with mild symptoms such as a vague ache or limited range of motion due to interference with a joint.
The tumor is applied to the surface at the end of the long bones. It has a very dense appearance, and may gradually wrap partly around the bone.
This tumor is treated with wide surgical removal. Chemotherapy is sometimes used depending on the grade of the tumor.
Complete Information on this Tumor
Introduction and Definition: 

Parosteal osteosarcoma is the most common form of surface osteosarcoma. It accounts for 5% of osteosarcoma cases. This lesion is frequently low grade.

Incidence and Demographics: 
This lesion is thought to originate from the periosteal layers of the bone. Patient's in their 20s and 30s are most commonly effected, with more female that males patients. The median age of patients is 27 years old.
Symptoms and Presentation: 

The tumor presents with a slow growing mass and mild pain. Occasionally, patients have no pain whatsoever. The most common locations are the distal femur near the back of the knee and the proximal humerus near the shoulder.

X-Ray Appearance and Advanced Imaging Findings: 
A large lobular dense mass appears on the surface of the bone near the joint. The lesion may initially be attached to the bone with a wide stalk, or appear as amount of dense material on the surface. The tumor may gradually extend itself out into the soft tissues and around the bone, and may almost encircled the bone if allowed to grow long enough. The medullary space of the bone is usually not involved but may become involved leg. The tumor may be very dense and appeared to be more dense than the adjacent bone. Usually, periosteal reaction is mild or absent.
Laboratory Findings: 
Noncontributory
Differential Diagnosis: 
Other surface lesions include myositis ossificans, periosteal osteosarcoma, osteochondroma.
Preferred Biopsy Technique for this Tumor: 
incisional
Histopathology findings: 
Parosteal osteosarcoma is a low-grade tumor microscopically. Approximately 80% of tumors are grade 1 and 20% are grade 2.2 Accordingly, it has a well differentiated spindle cell stroma, minimal atypia and a low mitotic rate. The tumor originates from the outer fibrous layer of periosteum. The fibroblastic stroma may have foci of trabecular bone or cartilage.
Treatment Options for this Tumor: 
Parosteal osteosarcoma has a relatively good prognosis compared to conventional osteosarcoma. Wide excision is the preferred treatment and there is normally no role for chemotherapy. Unfortunately, parosteal osteosarcoma can dedifferentiate into a higher grade tumor.
Preferred Margin for this Tumor: 
Wide. A marginal margin may be adequate if histologically negative
Outcomes of Treatment and Prognosis: 
Complete surgical removal of the low grade a variant of this tumor resulted in an excellent prognosis. Long-term survival of more than 80% of patients with this tumor is expected. Contaminated margins or positive margins are naturally associated with a high risk of recurrence and have a strong negative impact on overall prognosis.
Special and Unusual Features: 
In contrast to most osteosarcoma,parosteal sarcoma is often low grade. Therefore, complete surgical removal with a wide margin is curative, and chemotherapy is not used. However, a small proportion of these tumors contained high-grade areas and must be treated accordingly.
Suggested Reading and Reference: 
References Bloem, JL and HM Kroon, Osseous Lesions, Radiologic Clinics of North America, 31(2):261-277, March 1993. 2 Inwards, CY and KK Unni, Classification and Grading of Bone Sarcomas, Hematology/Oncology Clinics of North America, 9(3):545-569, June, 1995. Bullough, Peter, Orthopaedic Pathologv (third edition), Times Mirror International Publishers Limited, London, 1997. Huvos, Andrew, Bone Tumors: Diagnosis. Treatment and Prognosis, W.B. Saunders, Co., 1991. 1/22/98