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case_images: Timeline of disease diagnosis and treatment.
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case_images: The timeline of the disease diagnosis and treatment are presented in  Figure 1 . The patient first visited a local hospital on May 2019 owing to headache, nausea, and vomiting, and magnetic resonance imaging (MRI) revealed a tumor in the PF ( Figures S1A-C ). Ommaya reservoir implantation and subtotal resection of the tumor was performed at the local hospital ( Figures S1D-F ), and an initial pathological diagnosis of anaplastic ependymoma (WHO grade III) was established.
case_images: Histological and immunohistochemical analysis of the sphenoid sinus lesions. (A) Sheets of monotonous cells presenting as uniform, bland nuclei with evenly distributed chromatin, perivascular pseudorosettes and necrotic zones were observed on hematoxylin and eosin staining analysis. The tumor cells showed (B) dot-like epithelial membrane antigen (EMA) immunoexpression and (C) diffuse cytoplasmic glial fibrillary acidic protein (GFAP) immunoexpression suggestive of ependymal differentiation. (D) Ki-67 labelling index in the sphenoid sinus tumor was 60%, which showed a high proliferation fraction of the tumor cells. The tumor cells showed (E) immunonegative H3 K27-me3 staining and (F) immunopositive CXorf67 staining. Vascular endothelial cells in the tumor section were used as the positive control for H3 K27-me3 staining.
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case_images: Unfortunately, an MRI performed in February 2021 revealed scalp and sacrococcygeal metastases ( Figures S2A-D ). Later in March 2021, the patient underwent metastases (scalp and sacrococcygeal) resection at the local hospital, followed by whole-spine radiotherapy ( Figures S2E-H ). Histological examination revealed a tumor measuring 4x3x1.5 cm, with sheets of monotonous cells presenting as uniform, bland nuclei with evenly distributed chromatin on hematoxylin and eosin staining ( Figure 2A ). The tumor cells showed dot-like epithelial membrane antigen immunoexpression ( Figure 2B  ) and diffuse cytoplasmic glial fibrillary acidic protein immunoexpression ( Figure 2C  ) suggestive of ependymal differentiation. Ki-67 showed a high proliferation fraction of the tumor cells ( Figure 2D ). Immunohistochemical staining was negative for H3 K27-me3 staining ( Figure 2E ) and positive for CXorf67 staining ( Figure 2F ).
case_images: Illustration of mechanisms for extraneural metastasis of ependymoma.
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case_images: The results revealed sphenoid sinus, osseous, and pulmonary metastases ( Figures S3A-D ). Figure S4  ). Furthermore, transnasal endoscopic surgery was performed to resect the sphenoid sinus metastasis ( Figures S3E-G ), and the specimen was sent for pathological examination and genomic analysis.