Orbital Rhabdomyosarcoma With Unusual Histopathology in a Young Adult

A 22-year-old man presented with 1 month of worsening left upper eyelid ptosis and diplopia. Best-corrected visual acuity was 20/20 OU. Examination was notable for left eye proptosis, hypoglobus, supraduction deficit, and ptosis with reduced levator function. Magnetic resonance imaging showed a 2.2-cm enhancing extraconal superior orbital mass, which was excised via an anterior orbitotomy through an eyelid crease incision (Figure, A). Histopathology showed primitive, malignant cells arranged in sheets and nests, forming an alveolilike pattern, and an absence of strap cells, suggestive of alveolar rhabdomyosarcoma (Figure, B). However, myogenin staining was patchy, and the tumor lacked FOXO1 fusion, consistent with embryonal rhabdomyosarcoma.¹ The patient underwent chemotherapy and radiotherapy for microscopic residual disease. Rhabdomyosarcoma is the most common orbital malignancy in childhood with a mean age at onset of 7 to 8 years; less than 1% of reported cases occur in adults.² FOXO1 fusion–negative status, primary site in the orbit, and embryonal histopathology are favorable prognostic factors.³