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Surgery for Posterior Circulation Aneurysms


Clinical Pearls

  • Superior cerebellar artery aneurysms are often favorable for clipping because they tend to project laterally off of the midline, which places them directly in the well-visualized carotid-oculomotor triangle. They are associated with less morbidity than basilar apex aneurysms mainly because thalamoperforating vessels are often not involved.

  • Basilar apex aneurysms can be approached from many angles. If working through the Sylvian fissure, a full dissection separating the frontal and temporal lobes is helpful to maximize visualization and angles of freedom.

  • Careful preoperative inspection of the CT angiogram can help the surgeon determine the relationships among the parent artery, the aneurysm, and bone structures. In the case of basilar apex aneurysms, it is important to know if the aneurysm lies below, at, or above the clivus in order to formulate a surgical strategy.

  • The far lateral craniotomy is the workhorse surgical approach for posterior inferior cerebellar artery origin aneurysms. The exposure offers a view of the intradural vertebral artery for proximal control and provides adequate working space in the angle between the lateral medulla and inferior cerebellum to facilitate clipping.

  • The natural history of posterior circulation aneurysms is that they are more prone to rupture than aneurysms arising from the anterior circulation.

Background

Posterior circulation aneurysms (those located on the vertebral artery, basilar artery, and their branches) are often challenging lesions to treat surgically. They intrude among the lower cranial nerves and the brainstem in anatomically constrained corridors. Oftentimes significant bone must removed, such as portions of the occipital condyle, in order to maximize operative exposure and working angles. Unlike aneurysms of the anterior circulation, proximal control can be challenging, as in the case of basilar apex aneurysms. Although challenging, surgical treatment of these lesions can be approached methodically and with good results in properly selected patients. In addition to the anatomic and technical challenges associated with these aneurysms, their scarcity also makes it difficult to teach, and learn, how to master these lesions. In terms of incidence, they are relatively rare compared to their anterior circulation counterparts. Combined with the development of endovascular treatment techniques, even fewer are considered for surgical treatment. In clinical practice, the widespread preference for endovascular treatment often results in the few “complex” lesions that are not amenable to coiling or flow diversion being referred for surgical treatment. Therefore trainees and faculty alike must take maximum advantage of every case possible to gain the hands-on experience necessary to develop the unique skill set necessary for the safe surgical treatment of these aneurysms.

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