Discovered by using endoscopy, the CPA was divided into 4 levels: petrosal veinand arachnoid mater, acousticofacial bundle, trigeminal and abducens nerves, and lower cranial nerves(glossopharyngeal,vagus, and accessory).

• 内镜下由浅入深、由上至下可分为4层,即岩静脉层、面听神经层、三叉神经-外展神经层和低位颅神经层。