Ultrasound of Synovial Tumors and Tumorlike Conditions

The synovial membrane is prone to metaplasia and proliferation that is often benign, with extremely rare malignancy. Clinical presentation is nonspecific, and ultrasound, combined with radiography, is the first-line imaging technique. It detects synovial proliferation, effusion, and bone erosion with high sensitivity. It also guides biopsy, compensating for its low specificity. We review the ultrasound features of the main synovial tumors and tumorlike conditions, with a focus on the unique findings that enable a confident diagnosis or a limited differential diagnosis, and the ultrasound-guided synovial biopsy technique.