Mycotic pseudoaneurysm in the internal carotid artery secondary to cranial base abscess diagnosed with optic neuritis: a case report.

-induced mycotic aneurysm is difficult to treat and often has poor outcomes with severe symptom progression. Early diagnosis is also difficult, and blood and cerebrospinal fluid tests often fail to reveal any findings. A 74-year-old man presented with recurrent nosebleeds in addition to symptoms of left optic neuritis. Contrast-enhanced computed tomography scan revealed a left internal carotid artery pseudoaneurysm protruding into the left Onodi cells, which was identified as the origin of bleeding. Endovascular left internal carotid artery occlusion was performed. One month postoperatively, external ophthalmoplegia and disorientation occurred. Although antibiotic treatment was continued for 1 month, consciousness loss and haematemesis occurred, and a new contralateral right internal carotid artery pseudoaneurysm ruptured, which resulted in death. At autopsy, infection centred on the skull base was pathologically found, although the sinus mucosal surface was normal. This case suggested a mycotic infection secondary to optic neuritis resulted in a left infectious pseudoaneurysm that spreads to the skull base and formed an aneurysm on the contralateral side 4 months thereafter. Therefore, the possibility that features of the Onodi cells contributed to the spread of inflammation inside and outside the skull and were involved in the formation of aneurysms inside and outside the dura mater was considered for the first time.