Preoperative Considerations in Occipital Artery-high-riding Posterior Inferior Cerebellar Artery Bypass: A Report of Two Cases and a Literature Review.

Nonsaccular vertebral artery aneurysms involving the posterior inferior cerebellar artery (PICA) are rare. Treatment is considered a significant challenge because of their angiographic and anatomical features, especially in high-riding PICA. Therefore, meticulous preoperative angiographic and anatomical evaluation is necessary. Moreover, consideration of the distance between the cerebellar skull base and caudal loop of the PICA is important. We present two cases of occipital artery-high-riding PICA bypass and discuss important preoperative technical considerations.