"Tadpole tail sign" in high-grade synovial sarcoma of the ulnar nerve: a case report.

Synovial sarcomas of the peripheral nerve (SSPNs) are rare aggressive tumors with only a few cases documented in the literature. Among these, the involvement of the ulnar nerve was identified in seven patients, however without in depth radiological description. To the best of our knowledge, this is the first case report with high-resolution ultrasound, MR imaging and a histopathological description of a high-grade synovial sarcoma of the ulnar nerve. SSPNs are frequently misinterpreted as peripheral nerve sheath tumor making the diagnosis difficult and often challenging. Our case report highlights an unusual instance of a malignant synovial sarcoma originating from the ulnar nerve in a 28-year-old woman, which rapidly progressed with a worse outcome. We present the specific imaging and histological findings of this monophasic spindle cell type lesion with immunocytochemical markers, and describe a new "tadpole tail sign" on ultrasound, to allow its early recognition and prevent misdiagnosis.