Postradiation Extraskeletal Osteosarcoma Masquerading as an Axillary Artery Pseudoaneurysm.

BACKGROUND: A 68-year-old woman with a thoracoabdominal aortic aneurysm recently status after first-stage elephant trunk procedure with right brachiocephalic artery endarterectomy and reimplantation of the innominate and left carotid using a 14 × 10-mm branch graft presented to clinic with increasing pain in her right arm and shoulder for 2 weeks. She also had a remote history of radiation to the right axilla for breast cancer. On physical examination, she had a tender mass under her clavicle, numbness in shoulder and right hand weakness. Computed tomography scan revealed a 5.3 × 4.3-cm coarsely rim calcified lesion in the right axillary region reported as a pseudoaneurysm.

METHODS: She was taken to the operating room for exploration. After obtaining proximal and distal control, the mass revealed to be a solid tumor. The mass was removed, taking care to avoid the axillary artery and medial and lateral cords of the brachial plexus.

RESULTS: Pathology revealed an extraskeletal osteosarcoma.

CONCLUSIONS: Extraskeletal osteosarcoma is an extremely rare primary bone cancer, making up <1% of all osteosarcomas. Less than 350 cases are described in the literature. Of the cases described in the literature, less than 5% involve the upper extremity and/or thorax. They are aggressive tumors located in the soft tissue and not an extension of bone. Treatment involves multimodality therapy with surgical resection and adjuvant chemoradiation.