Rare presentation of primary synovial chondrosarcoma arising in the shoulder: a case report.

Synovial chondrosarcoma (CHS) is a rare malignant tumor arising from the synovial tissue and is often associated with synovial chondromatosis. Herein, we present a unique case of primary synovial CHS in the shoulder joint without evidence of synovial chondromatosis. A 60-year-old man presented to our hospital with a complain of left shoulder pain that persisted for 6 years, which was initially misdiagnosed as synovitis. Radiography revealed an osteolytic lesion involving the humerus and the scapula. Histologically, the tumor exhibited features of grade 2 synovial CHS, infiltrating the trabecular bones and intra-articular space. Wide resection led to a 9-year recurrence-free survival. This case underscores the challenges in diagnosing and managing synovial CHS, particularly in cases with atypical presentations lacking synovial chondromatosis, necessitating careful follow-up and adequate surgical intervention.