Results: A 47-year-old Japanese woman was admitted to hospital after a tumor was incidentally detected on a plain chest X-ray image. The tumor was located in the paravertebral region of the mediastinum and did not show any destruction of the thoracic vertebra radiologically. The tumor was clinically diagnosed as a benign neurogenic tumor and the tumor was easily removed surgically. Microscopically, the tumor mainly consisted of tumor cells with extensively vacuolated cytoplasm, arranged in cord-and nest-like fashion in a myxoid matrix background. Immunohistochemically, the tumor cells showed diffuse positivity for pancytokeratin (AE1/AE3), vimentin. The tumor cell nuclei were positive for brachyury, which is a key transcription factor of notochordal development.