Background: solitary fibrous tumour (SFT) has been documented in many other organs after its original pleural description. Orbital SFT is very rare and only 263 cases from the English literature are reported since 2021. The use of immunohistochemical markers is very helpful in the diagnosis especially CD34 positivity and STAT6 immunoreactivity.
Case report: A 50-year-old man presented with a 15 months history of progressive left exophthalmos. MRI showed a well-circumscribed, expansible soft tissue mass located above the right globe extending posterolaterally. The lesion was isointense to the extraocular muscles and cerebral cortex with strong enhancement with gadolinium. The patient underwent a left lateral orbitotomy. Total removal was achieved under a microscope and cryotherapy tool.
Results: By using an immunohistochemistry panel; the tumour was stained intensely for vimentin, CD34, and STAT6 and it was negative immunoreactivity to pancytokeratin (AE1/AE3), S100 protein, epithelial membrane antigen, glial fibrillary acidic protein, and FVIII. With 12 months follow-up, no recurrence was seen.
Conclusion: Orbit SFT is very rare. The generally accepted treatment for primary and recurrent orbital SFT is complete excision. The use of immunohistochemical markers is very helpful in the diagnosis. orbital SFTs are rare but can be reliably diagnosed based on the presence of characteristic morphologic features and STAT6 and CD34 immunohistochemistry. Nuclear staining of STAT6 is a useful diagnostic adjunct in conjunction with CD34 positivity to help delineate SFT from histologic mimics. Orbital SFTs are generally accepted as benign tumours with a favourable clinical course. However long term clinical follow-up is recommended.
Key words: Exophthalmos, Orbital neoplasm, lateral orbitotomy, Immunohistochemistry CD34+, STAT6, Solitary fibrous tumor