Solitary fibrous tumor of the orbit.

Solitary fibrous tumor (SFT) of the orbit is a very rare lesion that may be misdiagnosed as fibrous histiocytoma, hemangiopericytoma, or other orbital tumors. We present a 62-year-old man who presented with painless proptosis, 20 years following left eye enucleation for a presumed neurofibroma. On T2-weighted magnetic resonance imaging (MRI), a hypointense tumor almost filled his entire left orbit. There was no intracranial extension. The specimen obtained at orbital exenteration was consistent with the histologic, immunohistochemical, and electron microscopic findings of SFT. The tumor was positive for vimentin and CD34 staining but negative for S-100 protein and epithelial membrane antigen. Only nine other cases of SFT of the orbit have been documented in the literature. Recognition of SFT of the orbit as a distinct pathologic entity and further follow-up of published cases are needed to determine the prognosis of this rare lesion.