A Unique Case of Pediatric Orbital Nodular Fasciitis with a Confirmed USP6 Fusion Mutation.

Nodular fasciitis is a benign, pseudoneoplastic condition often misdiagnosed as sarcoma due to its rapid growth, high cellularity, and mitotic activity. Herein is reported a case of a 7-year-old patient with a painless, enlarging nodule in the left superolateral orbit. Ultrasound revealed a 7.5 mm cystic mass, which was excised via an upper eyelid crease anterior orbitotomy. Histopathologic studies showed benign spindle cells, and molecular testing identified a UBC::USP6 fusion, confirming the diagnosis of nodular fasciitis. Nodular fasciitis is most common in the limbs, trunk, and head or neck region, with fewer than 1% of cases occurring in the orbit. Molecular testing is critical in differentiating this condition from malignancies. Complete surgical excision is the preferred treatment, with a low recurrence rate of 1% to 2%. This is the first reported pediatric case of orbital nodular fasciitis with a UBC::USP6 fusion mutation.