Surgical and Endovascular Management of Patients With Giant Cerebral Aneurysms

Introduction

Giant cerebral aneurysms (GCAs) have been defined by convention as aneurysms that are 2.5 cm or greater in diameter. These lesions constitute approximately 5% of intracranial aneurysms and are the result of progressive enlargement of a small aneurysm . Descriptions of aneurysms as large as 8.5 cm in diameter exist in the literature . Despite advances in both surgical and endovascular techniques, the GCA continues to be a formidable pathologic condition to manage primarily because of dysplasia of the aneurysm wall (calcification or random thickening) and the involvement of the surrounding structures through compression or adhesion.

The most common presentation of a GCA is an aneurysm mass that results in compression of nearby structures. That such growth and displacement can occur before presentation is evidence to the resiliency of the optic apparatus that abuts the ophthalmic and anterior communicating segments where these lesions appear more frequently. Transient ischemic attacks (TIAs) or strokes from distal embolization of intraluminal thrombus is a less common presentation. Seizures can result from cortical compression or deposition of hemosiderin around the GCA which is often the presentation of GCAs of the middle cerebral artery.

Historically these lesions were thought to have a benign course, but now it is well established that GCAs have a malignant clinical course and should be treated with the goal of complete obliteration, reduction of the mass effect, and reconstruction of the cerebral vasculature . This chapter will focus on conventional microsurgical and endovascular management of GCAs. Regardless of the method of treatment, it is imperative that the cerebrovascular neurosurgeon remembers what Dr. Charles Drake observed in his study of giant aneurysms: “Every giant aneurysm is a unique entity and must be treated as such .”

Microsurgery

The basis for microsurgery of these formidable lesions has its foundation in three principles that apply to all GCAs in any location:

• 1.

  preparation and adequate exposure,

• 2.

  complete vascular control,

• 3.

  aneurysm decompression before clip placement.

In addition, each individual locus in the cerebral vasculature has its own subset of additional necessities for a successful surgery and a good patient outcome. During surgical reconstruction of a GCA, one must always entertain multiple treatment possibilities before committing to a surgical solution. Although clip reconstruction is a desired outcome, calcified atheroma and thrombosis may render these solutions impossible without parent vessel occlusion (PVO). For this reason, revascularization or trapping strategy should always be a potential component of the surgical plan for the GCA. Although it has been routine to preserve the superficial temporal artery during the treatment of these aneurysms, improvements in imaging and endovascular techniques have allowed for some refinement. The use of selective trial balloon occlusion (TBO) in the preoperative evaluation of the patient can provide improved knowledge of the necessary conduit for bypass and can also approximate a time window for temporary occlusion. Skull base approaches are invaluable in maximizing the workspace for the surgeon and should be carefully considered to allow for full GCA visualization, minimal manipulation of surrounding structures, and a relaxed and direct entry of the bypass conduit. Table 156.1 delineates useful techniques (by location) that should be implemented when treating GCAs.

Table 156.1

Summary of Surgical Strategies for Giant Cerebral Aneurysms (GCAs)

Anterior and posterior aneurysms present different surgical challenges that require various solutions. Some of the strategies are higher risk or more technically demanding than others, and it is imperative that these possibilities are entertained, if not routinely performed.

Green, routinely performed and accepted as a surgical option; yellow, increased risk or challenging surgical technique; red, high surgical morbidity/mortality and should be considered as the last option or not at all.

ACA , anterior cerebral artery; AChor , anterior choroidal artery; AComm , anterior communicating artery; ICA , internal carotid artery; MCA , middle cerebral artery; OA , occipital artery; OphA , ophthalmic artery; OZO , orbitozygomatic osteotomy; P1 , most proximal portion of PCA; PCA , posterior cerebral artery; PComm , posterior communicating artery; rec. Heub. , recurrent artery of Heubner; SCA , superior cerebellar artery; STA , superficial temporal artery; TBO , trial balloon occlusion; VB , vertebrobasilar.

The basic tenant of proximal and distal control is especially important in surgery for GCAs. It is mandatory to have access to all afferent and efferent vessels involved in the aneurysmal segment, and the consideration of cervical carotid exposure is important.

After exposure and circumferential dissection of the GCA, decompression of the aneurysm before the final clip placement is crucial. This frequently requires temporary artery occlusion/trapping, opening of the aneurysm dome, evacuation of intra-aneurysmal contents, and deflation to complete the reconstruction of the parent vessel. Without this maneuver, it is unlikely that the clip will fully occlude the orifice of the aneurysm entrance. Without complete closure the clip may also be driven on to the parent vessel, resulting in stenosis or occlusion. It is important to realize that the first clip is not the final clip.

The use of an ultrasonic aspiration device is useful in rapidly achieving removal of the aneurysm contents (clot or atheroma) that are preventing clip application. It is highly important that the contents are removed expediently, such that the focus of evacuation is on the aneurysm neck and not the fundus. Clearing the fundus does not facilitate clip placement and takes away precious temporary artery occlusion time. At times, complete dome resection may be necessary leaving a “tuft” of soft flexible neck tissue for clip reconstruction. This eliminates the “umbrella” effect in which a nonpliable, calcific, thrombotic, or previously coiled dome prevents an aneurysm clip from closing by rigidly holding the neck tissue open. This may be seen in lesions in which the aneurysm dome adheres to the overlying brain tissue.

Despite advances in clip technology, there may be persistent bleeding from the aneurysm after initial clip placement. Although direct observation may suggest adequate clip length across the neck, the possibility of redundant aneurysmal sac tissue in the clip blades should be considered. A fenestrated clip to “jump” the redundancy and to apply pressure directly on the redundant region may supply additional closing strength; this is a variant of a booster clip.

In lesions that do not contain partial thrombus, decompression of the intrasaccular contents for proximal carotid GCAs often requires the suction/decompression technique that was described initially at our institution. The proximal carotid artery being a common location, it is imperative that anyone treating these aneurysms be experienced in this technique or a variation of it. The neurosurgeon must remember that for these proximal lesions the control is in the neck. In conjunction with a distal temporary clip in place the aneurysm will collapse and permit clipping or emptying of the aneurysm contents as necessary. The contribution of the ophthalmic artery is often underappreciated. Failure to control “the ophthalmic” during suction/decompression may allow for reversal of flow during temporary clipping and filling of the aneurysm or bleeding during aneurysm repair. Initially suction and decompression was described as a direct carotid puncture with a 16-gauge angiocatheter connected to suction to reverse flow in the internal carotid artery (ICA) ( Fig. 156.1 ).

With more institutions building “hybrid suites” that have biplane angiography in an operating room, it has been increasingly common to obtain proximal control utilizing endovascular techniques ( Fig. 156.1 ). Although this replaces the neck dissection and carotid puncture, the use of anticoagulants and the intraluminal injury to the carotid artery are new risks introduced by these techniques. The comfort with either technique may vary by facility. There is no definitive evidence supporting one over the other.