This report describes a 68-year-old woman who presented with progressive, painless protrusion of the left eye. Findings included unilateral proptosis, superonasal displacement, motility restrictions, and dilated, tortuous conjunctival vessels. MRI and CT scans revealed a well-defined 41 × 19 mm orbital tumor extending along the lateral rectus muscle. Incisional biopsy revealed a spindle cell tumor with a fascicular to storiform pattern in a myxoid to collagenous stroma, showing mild to moderate cellular atypia and skeletal muscle infiltration. Immunohistochemistry was positive for smooth muscle actin and calponin, but negative for caldesmon and desmin. Next-generation sequencing identified an HMGA2-NAV3 gene fusion and amplifications of CDK4, MDM2, and GLI1. The findings were consistent with a low-grade myofibroblastic sarcoma (LGMS). The tumor was treated with en bloc orbital resection. No recurrence was observed after 18 months. This case highlights the role of histological and immunohistochemical evaluation in diagnosing this rare cause of unilateral proptosis.
Bendtsen et al. (Mon,) studied this question.