Solitary fibrous tumor of the conjunctiva with heretofore undescribed pathologic findings

A 37-year-old female presented with a conjunctival mass discovered 3 years prior. An excisional biopsy revealed a patternless proliferation of round and spindle-shaped cells with an eosinophilic fibrillary cytoplasm and vesicular nuclei with occasional inclusions. Psammoma bodies were arranged around the dilated irregularly-shaped vessels. Differential diagnoses included conjunctival solitary fibrous tumor (SFT), nevus, glomangioma, ectopic meningioma, and mesectodermal leiomyoma. The tumor cells were immunoreactive for CD34, CD99, bcl-2 and vimentin, and were negative for smooth muscle actin, desmin, glial fibrillary acidic protein, S-100 protein, epithelial membrane antigen, and human melanoma black-45. Ultrastructurally, the tumor cells had rough endoplasmic reticulum, free ribosomes, and scattered mitochondria without basal lamina or cellular junctions, which are features of fibroblasts. A diagnosis of SFT was rendered based on the light microscopic, immunohistochemical, and electron microscopic findings. We report here on the second case of a SFT arising in the conjunctiva, which clinically and histologically mimics conjunctival nevus, glomangioma, ectopic meningioma, and a hybrid neurogenic-myogenic tumor such as mesectodermal leiomyoma.