• Masahiro Oishi, Hironori Fujisawa, Katsuhiro Tsuchiya, and Yoshio Nakajima.
• Department of Neurosurgery, National Hospital Organization Kanazawa Medical Center, Ishikawa, Japan. Electronic address: ma-oishi@med.kanazawa-u.ac.jp].
• World Neurosurg. 2020 Sep 1; 141: 500-506.e1.

BackgroundHemangiopericytoma (HPC) is a rare mesenchymal tumor of the brain that occurs in the central nervous system as a solitary fibrous tumor. Surgical treatment of HPC is known to be beneficial, but results on the role of complete resection and adjuvant radiation are conflicting. However, it is often difficult to detect a central nervous system solitary fibrous tumor/HPC before surgery. We describe a presumed left trigeminal schwannoma that was histopathologically shown to be an HPC.Case DescriptionA 65-year-old man presented with paresthesia of the second and third branches of the left trigeminal nerve. Magnetic resonance imaging showed a tumoral lesion in the left cerebellopontine angle and Meckel's cave. We suspected a schwannoma and performed surgery, which resulted in only a partial resection because of tumor bleeding and unexpected intraoperative histologic findings. We could not achieve a definitive diagnosis. However, we observed local recurrence and disseminated lesions 5 and 6.5 years later, respectively. We performed a second surgery and were able to definitively diagnose the lesion as a grade III HPC based on the positive expression of STAT6 during immunostaining.ConclusionsAs solitary fibrous tumor/HPC requires gross total resection for effective resolution, it is imperative to consider it in the differential diagnoses of similar tumors. If an unusual pathologic image is found, we recommend rapid immunostaining for STAT6 to reach a definitive conclusion regarding the tumor type. This case highlights the importance of considering HPC when screening or diagnosing central nervous system lesions, especially in this rare location.Copyright © 2020 Elsevier Inc. All rights reserved.

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