A 50-year-old female presented with nausea and vomiting. She had a history of ulcerative colitis and had used steroids for over 30 years. She also had undergone aortic root surgery and mechanical valve insertion for an aneurysm of the ascending aorta at the age of 48, and hence, was taking a Vitamin K antagonist. A clinical examination showed an impairment of consciousness (Glasgow Coma Scale [GCS] score: E3V4M6). Her systolic blood pressure had increased to >200 mmHg. Her body temperature was normal. Laboratory studies showed a slightly elevated white blood cell (WBC) count and anemia. Her WBC was 11300/μL (normal, 3500–9000) and her hemoglobin level was 11.1 g/dL (normal, 11.5–16.6). In addition, her C-reactive protein level was 0.17 mg/dL (normal, <0.3). In coagulation tests, it was found that the patient’s prothrombin time-international normalized ratio was elevated to 2.47, and her D-dimer level had also increased to 5.7 μg/mL (normal, <1.0). Two sets of blood cultures and a urinary culture were negative. Brain computed tomography (CT) revealed a subcortical hemorrhage in the left occipital lobe and acute hydrocephalus due to intraventricular hemorrhaging []. No fluid or bone destruction was seen in the paranasal sinuses []. 3DCT angiography revealed a cerebral aneurysm in the distal left PCA []. During the examination, the patient suddenly became comatose. Emergency intubation and bilateral external ventricular drainage were performed under general anesthesia. On day 2, her consciousness level improved (GCS score: E1VtM4), and digital subtraction angiography was performed. The left vertebral angiography revealed a wide-necked aneurysm in the left parietooccipital artery (POA) [ and ]. Its maximum diameter was 5.6 mm. To prevent rebleeding, direct surgery was performed on the same day. The patient’s head was fixed in the prone position using a Sugita frame and the left occipital craniotomy was carried out. The location of the hematoma was confirmed by ultrasonography. A corticotomy was made in the superior occipital gyrus and the hematoma was approached []. The aneurysm was identified after removing the hematoma. The proximal and distal portion of parent artery were exposed and the location of the neck of the aneurysm was confirmed []. The parent artery had adhered to the neck of the aneurysm and an intra-aneurysmal thrombosis was found. As neck clipping would have been difficult due to the fragility of the neck of the aneurysm, the aneurysm was removed, and end-to-end anastomosis of the normal parts of the proximal and distal POA was performed [ and ]. A histopathological examination revealed that the elastic fibers had disappeared from the aneurysm wall and only fibrotic tissue was seen [ and b]. On the outside of the aneurysm, neutrophils and lymphocytes gathered and necrotic tissue was seen []. There were coenocytic hyphae in the necrotic tissue. Immunohistochemical analysis performed with Grocott’s stain revealed that the coenocytic hyphae varied in width and exhibited right-angled branching, which are characteristics of zygomycetes []. These findings were consistent with Mucormycosis. Postoperative CT and magnetic resonance imaging only revealed a small hematoma in the left occipital lobe, but no cerebral infarction. As status epilepticus occurred on postoperative day (POD) 1, the propofol-induced general anesthesia was maintained, and anticonvulsant drugs were administered. The patient’s cerebrospinal fluid (CSF) showed a slightly elevated cell count (117/μL) and a normal glucose level (96 mg/dL) on POD 7. Tests for serum β-D-glucan and Aspergillus antigen were negative on POD 9. After a definitive diagnosis was made based on a histopathological examination on POD 10, we administered 600 mg/day voriconazole. The patient’s consciousness level gradually improved and she was extubated on POD 10. Heparinization was performed to prevent thromboembolic events from POD 18. The source of the infection was not found during transesophageal echocardiography performed on POD 21 or contrast-enhanced whole-body CT conducted on POD 22. Six blood cultures and a CSF culture obtained after surgery were all negative. The patient’s condition suddenly worsened after vomiting on POD 31 and she died on POD 32. An autopsy revealed pneumonia in the dorsal section of the right lung. Aspiration pneumonia might have been the cause of death. No systemic fungal infection was found.