a 39-year - old man presented to the emergency department of soonchunhyang university bucheon hospital with disorientation and severe headache . 3d - ct angiography of the brain ( somatom sensation 16 ; siemens , forchheim , germany ) revealed a large aneurysm arising from the junction of the right anterior cerebral and the anterior communicating arteries that was oriented downward ( fig . this finding prompted emergent neurosurgical intervention , during which the aneurysmal neck was clipped successfully ( fig . , the patient 's mental status had improved and he complained of right eye vision loss . on ophthalmologic examination , the patient 's visual acuity was no light perception ( nlp ) od and 1.0 os and his right pupil was nonresponsive . in retrospect , the patient recalled noticing a visual field defect encroaching from the inferior field in the right eye 10 days before admission , but he thought it was a manifestation of headache . the results of dilated fundus examinations were normal in both eyes , and the optic nerves in particular appeared normal . after three months , the vision in the patient 's right eye remained nlp , and atrophy of the right optic nerve had occurred . with recent advances of ct and magnetic resonance imaging , the diagnosis and treatment of cerebrovascular disease have become more accurate and effective . acute retrobulbar optic neuropathy due to an anterior communicating artery aneurysm is rare , and to our knowledge 3d - ct angiographic images of this condition have never been reported . although sudden unilateral visual loss combined with signs of retrobulbar optic nerve dysfunction suggests a diagnosis of optic neuritis , especially when associated with normal looking discs , vascular and compressive lesions may be considered in certain cases . conventional ct revealed vascular pathology , and the choice of advanced vascular imaging modality was left to the physician . although conventional digital subtraction angiography ( dsa ) is considered the most sensitive tool for detection of intracranial aneurysms , we did not perform dsa because it is an invasive study . furthermore , considering the potential delays in time required to assemble the angiography team and perform the angiogram , ct angiography is often faster and is comparably accurate . magnetic resonance angiogram is another option , and it has advantages for the evaluation of cerebrovascular lesions . however , in our case , ct angiography was perceived to be faster and less likely to induce claustrophobia . although endosaccular occlusion of the intracranial aneurysm was considered in the present case , urgent decompression of the aneurysm could not be achieved by this treatment because of the volume effect of the coils . in our patient , immediate decompression was mandatory and emergent surgical decompression with clipping of the aneurysm was identified as the treatment most likely to rescue vision . there are several explanations for monocular visual loss due to a ruptured anterior communicating artery aneurysm , including direct bleeding into the optic nerve , direct compression by the aneurysm , and interruptions of blood flow to arteries supplying posterior portions of the optic nerve as a result of either the subarachnoid hemorrhage itself , subsequent vasospasm , or the surgical clipping of the aneurysm . the previous recognition of an inferior visual field defect 10 days before the attack suggests that direct compression of the optic nerve by the aneurysm was contributory .
three - dimensional computed tomographic ( 3d - ct ) angiography is a widespread imaging modality for intracranial vascular lesions . 
 however , 3d - ct angiograms of an anterior communicating artery aneurysm associated with acute retrobulbar optic neuropathy have not been previously described . 
 we present 3d - ct angiograms of an aneurysm of the anterior communicating artery that caused subarachnoid hemorrhage and vision loss in a 39-year old man . 
 the 3d - ct angiograms were consistent with findings identified directly during surgery .