Primary Osteosarcoma of the Skull Base Treated with Endoscopic Endonasal Approach: A Case Report and Literature Review.

Introduction Giant cell-rich osteosarcoma (GCRO) is a rare pathologic diagnosis, and most cases have involved the appendicular skeleton. We present a challenging diagnosis of GCRO of the skull base treated with an endoscopic endonasal approach. Case Presentation An 18-year-old female patient presented with acute monocular visual loss. Imaging revealed a large clival mass encasing the internal carotid arteries bilaterally with pituitary and optic nerve compression. The lesion was resected via a staged endoscopic endonasal approach and the patient's vision normalized postoperatively. The final pathological diagnosis was challenging and, after consultation with multiple North American centers, was concluded as GCRO. The tumor recurred and further surgery was performed, followed by adjuvant chemoradiation. Conclusion We highlight diagnostic challenges of GCRO of the skull base, and describe, with intraoperative pictures, successful surgical resection via an endoscopic endonasal approach. Based on our literature review, this is the first published case report of GCRO of the skull base.