Two cases of solitary fibrous tumor/hemangiopericytoma with different clinical features according to the World Health Organization classification: case report and review of the literature.

Solitary fibrous tumors (SFTs) and hemangiopericytomas (HPCs) have been classified as one entity by the World Health Organization in 2016 due to gene fusion between NAB2 and STAT6. In the Central Nervous System (CNS), a hypocellular, collagenized tumor with a classic SFT phenotype is considered grade I, whereas more densely cellular tumors mostly corresponding to the HPC phenotype are classified as grade II or III (anaplastic) depending in mitotic count (<5 vs. >5 mitoses per 10 high-power fields). Herein, we report two cases of targeted SFT/HPC in which pathological differences and WHO grading affect clinical features. A 75-year-old woman presented with headache and had an intradural extramedullary tumor at the C1 to C2 level. The tumor was well-circumscribed and attached only to the dura mater. It was totally removed and diagnosed SFT/HPC grade I. In contrast, a 68-year-old woman presented with numbness in the right upper limb and had an intradural extramedullary tumor at the medulla to C3 levels The tumor was irregularly marginated and strongly adherent to the spinal cord and involved the vertebral artery. It was sub totally removed and diagnosed SFT/HPC grade II. To the best of our knowledge, there are only 12 cases of SFT/HPC at the craniocervical junction, including the present two cases, of which four that were adherent to the spinal cord or involved the vertebral artery were grade II or III. Although the location of the tumor was almost the same, there were significant differences in the intraoperative findings according to the WHO grading. 2021 Journal of Spine Surgery. All rights reserved.