Reappraisal of morphological and immunohistochemical spectrum of intracranial and spinal solitary fibrous tumors/hemangiopericytomas with impact on long-term follow-up

Hemangiopericytomas (HPCs) and solitary fibrous tumors (SFTs) are unique entities in the central nervous system (CNS) and even rarer in the spine with propensity to recurrence and metastasis. Both these tumors were detected to share the NAB2-STAT6 fusion gene with frequent morphologic overlap that necessitated the need for the combined term SFT/HPC in the CNS by the World Health Organization (WHO) in 2016.This study aims to describe the clinical outcome of intracranial and spinal SFT/HPCs based on detailed histomorphologic and immunohistochemical features.A retrospective analysis of these tumors was conducted over a period of 10 years from January 2006 to January 2017 at our institute. Based on the elaborative assessment of morphology and immunohistochemistry, these tumors were categorized into three grades as per WHO criteria.A total of 13 cases were encountered involving mainly extra-axial and supratentorial regions. Among intracranial HPCs, anaplastic subtypes constituted significantly higher proportion (39%) when compared with peripheral HPCs. Peculiar morphological patterns like micropapillae and pseudoangiomatous arrangement of tumor cells were observed in high-grade tumors. A panel of immunomarkers were used to confirm the diagnosis and rule out other mimickers. Gross total resection was achieved in 54% (7/13) of the cases with local recurrence observed in 31% (4/13). Grade II tumors showed recurrence in 28% cases. No case showed distant metastasis.To conclude, not just clinical parameters but morphologic features such as unusual patterns, mitosis, and proliferative index also play a pivotal role in predicting the clinical behaviour of SFT/HPC.