Idiopathic distal anterior choroidal artery aneurysms are particularly rare. Their diagnosis and treatment strategy are difficult because of the particular characteristic of pathological anatomy. Our case presented with intraventricular hemorrhage mainly. His idiopathic aneurysm was located in the trigone of undilated ventricle. Computed tomographic angiography demonstrated both the precise aneurysm and parent artery even when there was no dilated parent artery for the first time. It is also the first time to resect this tiny aneurysm assisted by frameless stereotactic guidance during operation after absorption of intraventricular blood. Computed tomographic angiography and frameless stereotactic guidance benefit the diagnosis and treatment of this kind of aneurysms. Sacrificing plexual AChoA did not cause any neurologic deficit.