Posterior mediastinal soft-tissue Rosai–Dorfman disease mimicking a neurogenic tumor

Rosai–Dorfman disease (RDD), a rare non-Langerhans cell histiocytic disorder that primarily involves lymph nodes, rarely manifests as isolated posterior mediastinal extranodal lesions. We report a woman in her 30s with incidentally detected paravertebral masses in the posterior mediastinum on routine screening. Contrast-enhanced CT showed progressive homogeneous enhancement of the lesions; MRI revealed T1 isointensity, mild T2 hyperintensity, and marked fat-suppressed T2 hyperintensity relative to muscle. A neurogenic tumor was initially suspected. Video-assisted thoracoscopic excision established RDD: large pale histiocytes with emperipolesis, S100 and CD68 positive, CD1a negative. The patient had an uncomplicated postoperative course, with no clinical or radiologic recurrence over 2 years of follow-up. This case underscores extranodal soft-tissue RDD as a rare mimic of posterior mediastinal neurogenic tumors, highlighting the need for mandatory radiologic-pathologic correlation to prevent misdiagnosis and guide surgical management and long-term surveillance.