Orbital solitary fibrous tumor

We present the case of a 46-year-old man who complained of progressive right lower eyelid swelling associated with diplopia when looking down. A nontender mass over the right lower palpebral conjunctiva with vessel engorgement and limited downward gaze were found. Magnetic resonance imaging (MRI) demonstrated a well-defined nodular lesion occupying the inferior area of the orbit. After surgery, a pathological examination revealed that the lesion was a well-encapsulated fibrous tumor composed of spindle cells with a whorl-like arrangement and collagen formation. Immunohistochemical staining was positive for vimentin, CD34, and CD99. The Ki-67 level was relatively low, diagnostic of a solitary fibrous tumor. Our case showed a typical presentation of an orbital solitary fibrous tumor with slow progression, MRI images of a homogenous isodense lesion in T1, heterogeneous isodense lesion in T2, and positive vimentin, CD99, and CD34 on cytological analysis. This case shows that a combination of history, radiology, and pathology results is crucial to differentiate soft-tissue tumors in the orbit.