Postradiation Extraskeletal Osteosarcoma Masquerading as an Axillary Artery Pseudoaneurysm

Area of Science:

• Oncology
• Surgical Pathology
• Radiology

Background:

• A 68-year-old woman presented with right arm and shoulder pain, a palpable mass, and neurological deficits.
• Imaging revealed a large, calcified lesion in the right axillary region, initially suspected to be a pseudoaneurysm.
• The patient had a history of thoracoabdominal aortic aneurysm repair and prior radiation therapy to the right axilla for breast cancer.

Observation:

• Surgical exploration of the axillary mass revealed a solid tumor.
• The tumor was successfully resected while preserving the axillary artery and brachial plexus.
• The initial diagnosis of pseudoaneurysm was revised based on intraoperative findings.

Findings:

• Pathological examination confirmed the diagnosis of extraskeletal osteosarcoma.
• Extraskeletal osteosarcomas are rare, accounting for less than 1% of all osteosarcomas.
• This case is notable for its occurrence in the upper extremity/thoracic region, representing less than 5% of reported cases.

Implications:

• Extraskeletal osteosarcomas are aggressive soft tissue tumors distinct from bone.
• Multimodality treatment, including surgical resection and adjuvant chemoradiation, is the standard of care.
• This case highlights the importance of considering rare diagnoses in patients with complex medical histories and atypical presentations.