Aneurysms of the posterior cerebral circulation account for only about 15 % of all intracranial aneurysms, and surgical treatment of these aneurysms was demanding until the introduction of endovascular therapy. The surgery-related morbidity and mortality—about 10 % in the best published series—was correspondingly high. One must assume that in the average series, the surgery-related morbidity and mortality may have been about 30 % or higher. Part of the high complication rate can be linked to the relative rarity of these aneurysms, because the particular approaches and techniques require special skills and awareness of specific pitfalls. Another reason for the unsatisfactory results of microsurgical treatment, however, has certainly been the highly eloquent territory supplied by the parent arteries of these aneurysms—that is, the brainstem. Drake and Peerless from London, Ontario, acquired the world’s largest experience in the surgical treatment of aneurysms of the posterior circulation [1].

The difficult surgical therapy for aneurysms of the basilar artery led to the acceptance of endovascular therapy as the treatment of first choice prior to the general acceptance of endovascular coiling. In the late 1990s, it was shown that the treatment-related morbidity and mortality after endovascular treatment was lower than after microsurgical operation. Thus, the endovascular treatment of basilar artery aneurysms was established 3–4 years before the general acceptance of endovascular therapy for ruptured aneurysms in the wake of the International Subarachnoid Aneurysm Trial (ISAT), the results of which were first published in 2002.

The acceptance of the superiority of endovascular treatment techniques applies not to all aneurysms in the posterior circulation, but particularly to aneurysms of the basilar artery. Of all ruptured and unruptured aneurysms of the posterior circulation, the aneurysms of the basilar bifurcation account for approximately 50 %. The next most common locations are the origin of the superior cerebellar artery (SCA) and the origin of the posterior inferior cerebellar artery (PICA), each with about 15 %. Other sites of saccular and fusiform aneurysms of the posterior circulation are the junction of the vertebral arteries and the origin of the anterior inferior cerebellar artery (AICA). Aneurysms occur rarely at the origin of the posterior communicating artery from the posterior cerebral artery, as well as in the peripheral portions of the posterior cerebral artery and the peripheral portions of the SCA, AICA, and PICA. These latter groups each account for a few percent of all aneurysms of the posterior circulation. Special situations are dissecting aneurysms, especially of the vertebral artery, fusiform vertebrobasilar aneurysms in the context of arterial ectasia and elongation (megadolichobasilar artery), and aneurysms of the feeder arteries of posterior fossa arteriovenous malformations. Each of these special situations accounts also for a few of all aneurysms of the posterior circulation.

Endovascular treatment of aneurysms of the basilar bifurcation and aneurysms at the origin of the SCA and AICA has become so well established that microsurgical competence has been lost and microsurgical therapy is no longer available as an alternative for these aneurysms. The situation for saccular aneurysms at the origin of the PICA from the vertebral artery is different; both endovascular and microsurgical therapies currently appear to be equivalent [2]. It remains unclear which treatment modality provides better short-term and long-term results, on the average. Finally, endovascular treatment of peripheral aneurysms is currently difficult. From the endovascular side, only obliteration of the carrier artery may be offered, which generally results in territorial cerebellar infarction. Therefore, peripheral aneurysms remain the domain of microsurgery.