Orbit Solitary Fibrous Tumor: A Proposed Risk Prediction Model Based on a Case Series and Comprehensive Literature Review

Abstract

Solitary fibrous tumors (SFTs) of the orbit are rare. In order to further characterize the clinical and pathologic features of solitary fibrous tumor arising at this anatomic site, 12 cases of orbital SFTs were analyzed in conjunction with a review of 263 cases reported from the English literature in order to develop a risk prediction model. SFTs of the orbit were equally distributed between males (n = 5) and females (n = 7) with a mean patient age of 46.8 years (median 44.5 years; range 18-76 years) at initial diagnosis. The patients typically presented with swelling or mass around the orbit, with proptosis (n = 10), ptosis (n = 5), and visual changes (n = 6). Tumors were orbital (n = 10) or upper eyelid (n = 2). Mean tumor size was 2.5 cm (median 2.6 cm). Microscopically, the tumors were characterized by cytologically bland spindle cells with patternless growth, hypocellular and hypercellular areas, variable amounts of collagen, and ectatic, branching blood vessels. By immunohistochemistry, all cases had a strong nuclear STAT6 expression. All patients were initially managed with excision or biopsy, three with presurgical embolization. The two patients with biopsy only had persistent disease (mean 37.2 months), but a third patient developed distant bone metastasis at 86.9 months. Overall mean follow-up was 73.1 months: 9 patients are alive or dead without disease (mean 77.9 months), two patients with persistent disease, and one patient with metastatic disease at last follow-up (102 months). Incorporating cases sufficiently reported in the literature, a risk prediction model based on age > 45 years, tumor size > 3 cm, tumor necrosis, mitoses of > 4/2 mm², moderate to high cellularity, and moderate to severe pleomorphism allows for risk stratification for the development of local recurrence and distant metastasis. In conclusion, orbital SFTs are rare, but can be reliably diagnosed based on the presence of characteristic morphologic features and STAT6 immunohistochemistry. Orbital tumors tend to show a higher frequency of local recurrence than distant metastasis, which can be predicted by a risk stratification model unique to orbital tumors. With late disease common, long term clinical follow-up is recommended.

Keywords: Follow-up studies; Immunohistochemistry; Orbital neoplasms; Risk assessment; STAT6; Solitary fibrous tumors.

Fig. 1

a) Clinical photo showing left globe displacement and a superior eyelid swelling. b) Coronal T1 SE FS MRI of an extraconal medial right orbit bright signal mass (arrow). C) Computed tomography of a large retrobulbar mass (arrow) resulting in significant proptosis. d) Embolic material (arrow) can be seen in this medial left orbit mass

Fig. 2

a) Very well circumscribed tumor with a predominantly heavy, keloid-like collagen deposition. b) This solitary fibrous tumor expanded into the adjacent fat, but seemed to incorporate it, rather than being a lipomatous variant. c) Cellularity could vary from one area to another within the same tumor. d) Hypocellular regions with a more edematous appearance to the stroma

Fig. 3

Various patterns in SFT. a) Hemangiopericytoma-like vessels with a non-descript spindled cell proliferation. b) Short, tight, cellular fascicles could be seen. c) Classical appearance of bland spindled cells set within a collagenized stroma with open vessels. d) Myxoid change within the stroma could be seen in some tumors

Fig. 4

a) Strong, diffuse nuclear STAT6 reaction in a classical SFT. b) Strong and diffuse cytoplasmic CD34 immunoreactivity. c) Embolic material within a classical SFT pattern. d) STAT6 (left side) immunoreactivity is lost in the rest of the tumor adjacent to areas of embolization