Solitary Fibrous Tumor/Hemangiopericytoma: A Companion Case Discussion of a Spectrum of Rare CNS Mesenchymal Tumors and Their Evolving WHO Classification

The combined term solitary fibrous tumor/hemangiopericytoma was recently introduced in the World Health Organization Classification of Tumors of the Central Nervous System 2016 revision. The consolidation came amid mounting evidence that these 2 mesenchymal tumors are closely related, or even identical, entities. These neoplasms demonstrate significant clinical and demographic overlap, often indistinguishable imaging features, and a shared nerve growth factor inducible-A-binding protein 2/signal transducer and activator of transcription 6 gene fusion. We presented 2 cases of this uncommon entity and discussed its evolving tumor classification.