Orbital solitary fibrous tumor: encompassing terminology for hemangiopericytoma, giant cell angiofibroma, and fibrous histiocytoma of the orbit: reappraisal of 41 cases

Hemangiopericytomas and solitary fibrous tumors are uncommon neoplasms found in many locations, including the orbit. Both mesenchymal neoplasms share several clinicopathologic features, thus prompting intense debate as to whether they are variants of the same entity or merit separate designations in the orbit. These 2 entities, with the addition of giant cell angiofibroma of orbit, are of benign- to uncertain-behavior, CD34-positive, collagen-rich, specialized fibroblastic tumors, which may have overlapping or histologically identical features. In addition, so-called fibrous histiocytoma of orbit, a previous designation, has overlapping morphologic features with these tumors. To date, a large series of these collagen-rich fibroblastic tumors of the orbit has not been fully explored. Forty-one fibroblastic orbital tumors, originally diagnosed as hemangiopericytomas (n = 16), fibrous histiocytomas (n = 9), mixed tumors (hemangiopericytomas/fibrous histiocytoma) (n = 14), and giant cell angiofibromas of orbit (n = 2) between 1970 and 2009, were retrieved from our consultation files, the Ophthalmic Registry, at the Armed Forces Institute of Pathology. Slides and clinical records were reviewed, analyzed, and compared. Immunochemistry was performed for CD34, CD99, Bcl-2, Ki-67, and p53. Upon histologic review, all cases were reclassified as solitary fibrous tumor (41/41). The patients included 23 (56%) males, 17 (41%) females, and 1 unknown, with a mean age at presentation of 40.7 years (range, 16-70 years). The sites of involvement were the right orbit in 18 (44%) cases and the left in 16 (39%) cases. Tumors ranged in size from 0.4 to 5.0 cm (mean, 2.2 cm). Seventeen (41%) patients presented with an orbital mass, 8 (20%) with proptosis, 2 (5%) with painful mass, and 2 (5%) with painless mass. Duration of symptoms ranged from 3 to 96 months, with a mean of 23 months (median, 9 months). Microscopically, all lesions showed considerable similarity, varying in degree of cellularity, stromal collagen, and the presence of giant cells. Overlapping features with soft tissue giant cell fibroblastoma were observed. Immunochemistry revealed positivity for CD34 in all cases (100%), p53 in 85%, CD99 in 67.5%, and Bcl-2 in 47.5%. Although Ki-67 labeling was seen in all cases, it ranged from less than 1% in 54.3% of cases to 5% to 10% in 20% of cases. Taken together, the findings of this study suggest that orbital hemangiopericytoma and some cases previously designated as fibrous histiocytoma, giant cell angiofibroma of orbit, and solitary fibrous tumor have overlapping morphologic and immunohistochemical features and should be designated as solitary fibrous tumor. Adipocytes and unusual multivacuolated adipocytic cells may be present in these tumors, as well stromal myxoid change; and even stromal intramembranous ossification can be observed. There are overlapping features of orbital solitary fibrous tumor with another CD34-positive specialized fibroblastic tumor of soft tissue, giant cell fibroblastoma. Morphologic criteria for uncertain behavior to low-grade malignant ocular solitary fibrous tumors can be made by cytologic atypia and increased mitotic activity, but overall outcome for malignant solitary fibrous tumors of the eye should be further explored.