Solitary fibrous tumor of the orbit.

Painless unilateral proptosis is a frequent manifestation of numerous orbital neoplastic and non-neoplastic processes. Various mesenchymal tumors of both fibrohistiocytic and vascular origin are well-described causes. Solitary fibrous tumors (SFTs) are rare spindle-cell neoplasms usually found associated with serosal surfaces, especially the pleura, but they have recently been described in a number of extrapleural sites including the orbit. The authors describe the case of an 18-year-old man who presented with a 6-month history of painless proptosis in the right eye. A visible nontender mass in the right supermedial orbit producing ptosis of the upper lid was present. Magnetic resonance imaging (MRI) showed a well-circumscribed soft tissue mass located above the right globe with no obvious invasion of adjacent orbital structures. Uneventful surgical excision through a right frontal-orbitotomy approach was performed. Histological evaluation showed a solid, highly vascular tumor mass composed of spindle cells arranged in short ill-defined fascicles. Intense immunohistochemistry staining for CD34 and B-cell lymphoma 2 (BCL-2) differentiated the lesion from the more common hemangiopericytoma. Though considered benign, local recurrence and extraorbital extension of orbital SFTs have been described. Malignant behavior, including distant metastases, has been documented in as many as 20% of pleural cases with mortality rates as high as 50%. The natural history of this tumor in the orbit is unclear. The authors report the 35th case of orbital solitary fibrous tumor and discuss the differential diagnosis, histopathology, radiological features, and clinical course.