Differentiating between Mycotic and Dissecting Aneurysms in a Case of Ruptured Distal Superior Cerebral Artery Aneurysm

OBJECTIVE: We present a case of subarachnoid hemorrhage (SAH) due to ruptured mycotic aneurysm found in the distal superior cerebellar artery (SCA). CASE PRESENTATION: A 64-year-old man was admitted to our hospital with sudden unconsciousness. He had a history of alcoholism but no family history of SAH. Computed tomography (CT) showed apparent SAH; however, CT angiography (CTA) showed no apparent cause of SAH except for two small aneurysms in the same branch of the left distal SCA. We suspected mycotic aneurysm and prescribed antibiotics. It was difficult to diagnose the condition as mycotic aneurysm because there were no vegetations or caries at the time of admission. Because there were two aneurysms in the same branch with partial dilatation and stenosis, we suspected dissecting aneurysm, but continued to administer antibiotics for possible mycotic aneurysm. After the first operation, we diagnosed mycotic aneurysm because a vegetation and valve degeneration was found. CONCLUSION: It is difficult to distinguish mycotic aneurysms from dissecting aneurysms because of similar appearance on imaging, especially if no vegetation is found. Nevertheless, it is important to start treatment for mycotic aneurysm. If there is the possibility of mycotic aneurysm, appropriate antibiotics should be administered, and endovascular treatment could be considered for patients with deteriorating conditions.