A 32-year-old Chinese female patient was admitted to the hospital with "fever, cough, and shortness of breath for 20 days." A chest CT that was performed at the local hospital indicated tuberculosis, and the lesions increased in size after anti-tuberculosis treatment. Later, the patient went to our hospital. The patient's physical examination showed that she had wheezing that could be heard and was scattered in both lower lungs, and 80 mm x 80 mm skin ulcers were seen on her right lower extremity. An auxiliary examination included a chest CT, which showed large patches, patchy increased densities in both lungs, and multiple bronchial stenoses in both of her lungs (Figure 1a). Her ANCA was positive, Anti-protease 3 (anti-PR3) antibody was increased; she had anemia and high white blood cell and platelet counts. She also had increased C-reactive protein, erythrocyte sedimentation rate, anti-nuclear antibody spectrum, and anti-cyclic citrullinated peptides. The level of antibody was normal. The patient's urine protein was 2+, and urine occult blood was 3+. Multiple sputum and alveolar lavage samples were negative for tuberculosis bacteria; the patient's clinical diagnosis was GPA. For her treatment, she was given methylprednisolone sodium succinate combined with CYC for anti-inflammatory and immune suppression. Because the patient was intolerant to CYC and experienced severe nausea and vomiting, she was treated with rituximab (RTX) combined with steroids. After 1 year, the patient developed new symptoms such as dizziness and headache. A cranial MRI showed that she had an irregular mass that was seen in the fourth ventricle, with a larger cross-section of approximately 21 mm x 24 mm, which spread along the bilateral lateral foramen of the fourth ventricle. The sinus bone and surrounding pia mater were intact, and tumorous lesions were suspected (Figure 1b and c). The clinician performed a craniotomy to excise the mass. During the operation, a gray and red mass in the fourth ventricle (25 mm x 20 mm x 20 mm in size, with an abundant blood supply and a tight adhesion with the surrounding tissues, invading the dorsal side of the brainstem) was removed and was submitted for a pathological evaluation. Macroscopy revealed a gray-red mass that measured 25 mm x 20 mm x 20 mm, was soft, and had local bleeding and necrosis but no capsule. The microscopic features included vasculitis, granuloma, and necrosis, manifested by the infiltration of plasma cells, lymphocytes, and neutrophils in the walls of arterioles, venules, and capillaries. The presence of fibrinoid necrosis was not obvious (Figure 2b and c), and a large number of epithelioid cells were around the blood vessels. Surrounding the formation of granulomatous vasculitis (Figure 2d and e), the necrosis included liquefaction necrosis that formed abscesses. The epithelioid cells around the abscesses were arranged in a fence to form granulomas, and there were a large number of neutrophils, lymphocytes, tissue cells, and a small amount of plasma cell infiltration (Figure 2a). Immunohistochemistry was positive for CD68 (Figure 2f) and was negative for glial fibrillary acidic protein (GFAP). Acid-fast staining and silver hexaamine staining were negative. After combining the patient's clinical history, serology, imaging, pathological diagnosis, she was diagnosed with fourth ventricle GPA. After 5 months of follow-up, the patient's lung lesions and skin ulcers had completely resolved, but her brain lesions had further progressed (clinical data is shown in Table 1).