35.1 Introduction

The advent of endovascular techniques has changed the modes of treatment for intracranial aneurysms. Open surgical techniques, which were the treatments of choice competing with the potential course of aneurysm-related affections, are now being challenged by the less-invasive endovascular techniques. However, surgery remains the definitive treatment option for intracranial aneurysms, particularly for complex or broad-based lesions.1,2,3,4 The purpose of treatment is to completely occlude the aneurysm while preserving the flow in the involved parent, branching, and perforating arteries and avoiding affects on surrounding neural structures. Based on microsurgical principles of dissection and exposure, the quality of clip placement is mainly maintained and assured by direct intraoperative inspection. However, microscopic visualization is limited by the straight line of view. Complete occlusion of the aneurysm and preservation of all involved vessels cannot always be confirmed with the microscope. The incidence of unexpected residual filling of clipped aneurysms ranges from 4 to 19%,4,5,6,7,8,9 and the incidence of parent artery occlusion, from 0.3 to 12%.4,5,6,7,8 This high number of aneurysm remnants and accidentally occluded arteries remains challenging. A reduction of these adverse results is important to keep aneurysm clipping a competitive alternative to interventional procedures. The application of additional methods for imaging like intraoperative microvascular Doppler sonography and near-infrared indocyanine-green videoangiography for direct intraoperative neurovascular assessment have been introduced to the neurosurgical armamentarium and seem to be used on a regular basis.10,11,12,13,14,15,16,17,18 However, those imaging techniques are also limited to a straight line of view. The use of high-quality rigid endoscopes provides excellent wide-angle, close-up visualization of areas hidden from microscopic view. The enhancement of the visual field before, during, and after microsurgical aneurysm occlusion seems to be a safe and effective method to increase the quality of treatment.19,20,21,22,23,24,25,26

35.2 Indications/Contraindications

Aneurysm surgery remains a serious matter and even the most experienced neurovascular surgeons never consider it a routine job. To promote the greatest patient safety, the surgeon should consider every resource available to strengthen his or her confidence and results intraoperatively.

The usual way to assure complete aneurysm occlusion and flow in the involved vessels is by direct visual inspection. Under microscopic view, the restriction of the visual field to the direct line of sight often makes this difficult or impossible. For example, for the microscope, the possibility to look around anatomical structures or to inspect the backside of an aneurysm is limited by the boundary of the exposure and the extent of craniotomy. Microsurgical dissection and careful retraction of the aneurysm might provide some visual information of the backside and formerly hidden corners. On the other hand, even gentle aneurysm or vessel retraction and overexposure of the aneurysm may lead to intraoperative rupture. Endoscope-assisted techniques in the field of neurosurgery have proven to be beneficial in these situations, for the following: first, the endoscope provides increased light intensity in the depth of the operative field; second, it provides a clear close-up view of pathologic anatomical detail, and third, it offers extended viewing angles.19,20

From the classic microsurgical pterional or frontolateral approach, aneurysms such as those of the posterior communicating artery (PComA), anterior choroidal artery (AchoA), or internal carotid artery (ICA) are often located on the far side of the vessel. Aneurysms of the basilar tip area (basilar artery [BA], superior cerebellar artery [SCA], and posterior cerebral artery [PCA]) are often obstructed by anatomical structures. Especially with aneurysms in these locations, the authors suggest that additional endoscopic visualization is of value (Fig. 35.1, Table 35.1). But apart from that, it happens consistently that intraoperative findings are more complex than expected and a second perspective is helpful (Fig. 35.2). In this regard, it is important that endoscopic devices are available at every aneurysm surgery for use by the operating surgeon whenever needed.

Abbreviations: MCA, middle cerebral artery; AComA, anterior communicating artery; ICA, internal carotid artery; PComA, posterior communicating artery; BA, basilar artery; OphthA, ophthalmic artery; PerA, pericallosal artery; ACA, anterior cerebral artery; PICA, posterior inferior cerebellar artery; VA, vertebral artery; AchoA, anterior choroidal artery; SCA, superior cerebellar artery; PCA, posterior cerebral artery.

Source: Data from Fischer et al 2012.25

^a The results of a retrospective video analysis of 180 cases, in which an endoscopic postclipping control was performed. The quantity, distribution, and resulting clip rearrangements due to the endoscopic findings are listed.