Clinical Outcomes and Histopathologic Features of Orbital Hemangiopericytoma/ Solitary Fibrous Tumors

Purpose: Hemangiopericytoma is a mesenchymal tumor uncommonly found in the orbit. Histologically it is considered as part of a spectrum that also includes solitary fibrous tumor, with no clear differentiation between the two. Rate of transformation to metastatic disease vary between different series and have been reported in up to 15% of case. The purpose of this report is to review clinical and pathologic characteristics and treatments in recent patients with a diagnosis of both metastatic and non-metastatic orbital hemangiopericytomas/solitary fibrous tumors.

Methods: A retrospective review of all consecutive patients treated by the senior author (BE) between 2003 and 2016. The clinical and radiographic findings at presentation, the histologic features, as well as treatments, follow-up time and status at last contact were recorded.

Results: Six patients (4 men and 2 women) were identified. Average age at diagnosis was 51.5 years (range: 31–73, median: 50 years). Three patients had a primary tumor at presentation, one was treated with complete surgical excision and is alive without evidence of disease after15.8 months of follow-up. The other two patients with primary tumor were lost to follow-up. Three patients had a recurrent orbital disease at presentation; two developed metastatic disease to the lungs (2 patients) and liver (1 patient) and at the time of this report are alive and being treated with systemic chemotherapy. The other patient with recurrent orbital disease at presentation has unfortunately died of her disease. Histologic features of all patients included spindle cell tumors positive for CD34, STAT6 or both. Patients with metastatic disease had an increased mitotic activity and K_i-67 index compared with the rest of the patients in this series.

Conclusion: Hemangiopericytomas/Solitary fibrous of the orbit can be benign or malignant and with a clinical and biologic course that varies from a slow-growing mass, to an aggressive recurrent and possibly metastatic tumor. While immunohistochemical stains are helpful for correct diagnosis, mitotic rates and K_i-67 index may correlate with malignant potential of the tumor. Metastatic disease was not uncommon in our series.