Adult Rhabdomyosarcoma of Ethmoid Sinus Recurring as an Orbital Mass.

Alveolar rhabdomyosarcoma (RMS) is a primitive, malignant, round cell neoplasm derived from mesenchymal tissue that exhibits partial skeletal muscle differentiation. We describe a rare case of alveolar RMS of ethmoid sinus, recurring as an orbital mass. A 23-year-old man with the chief complaint of anosmia and mild proptosis was diagnosed with RMS of the left ethmoid sinus and orbit following an endoscopic biopsy of the mass. He was treated with chemotherapy and radiotherapy. At 12 months after diagnosis, while still on maintenance chemotherapy, he presented to our eye hospital with a large medial canthal mass and lateral globe displacement. Orbital computed tomography revealed an extraconal mass in the medial orbit of the left eye, extending posteriorly and compressing the medial rectus muscle. Notably, the ethmoid sinus was clear. Incisional biopsy was performed and the recurrence of alveolar RMS was confirmed. Alveolar RMS of the ethmoid sinus may recur as an orbital mass, even if the sinus where it originated is clear at the time of recurrence.