Dissecting Aneurysm of Anterior Inferior Cerebellar Artery Initially Presenting with Nonhemorrhagic Symptom.

We report a patient with a probable dissecting aneurysm of the anterior inferior cerebellar artery (AICA) initially presenting with a nonhemorrhagic symptom, which resulted in subarachnoid hemorrhage. A 61-year-old woman suddenly experienced nausea. Computed tomography (CT) on admission showed a high-density mass with a double lumen in the right cerebellopontine angle without subarachnoid hemorrhage. Five days after the onset, she suddenly lost consciousness. CT demonstrated subarachnoid hemorrhage. Emergency angiography revealed a probable dissecting aneurysm at the lateral pontomedullary segment of the right AICA. Although the initial symptom is not hemorrhage, an unruptured dissecting aneurysm of the AICA may have a high risk of rupture. Immediate radical treatment to prevent subsequent rupture is necessary for even an unruptured dissecting aneurysm of the AICA.