Special Considerations: Giant Aneurysms, Bypasses, Previously Coiled Lesions, and Rare Locations
Giant aneurysms, defined as lesions measuring at least 2.5 cm in maximal dimension, demand great technical expertise and creativity if a surgeon hopes to achieve good results in a reliable fashion. There is no one method to treat these complex lesions, and the exact technique chosen must depend heavily on the specific situation. If local mass effect is a significant issue, then some treatment that will enable emptying and deflation of the lesion should be considered. This may include direct clipping, aneurysmorrhaphy with reconstruction, or trapping with distal revascularization. When mass effect is not a problem, a simple parent artery occlusion with distal revascularization may be sufficient. Although cranial neuropathy resulting from local pressure exerted by a small aneurysm has been shown to resolve with endovascular therapy, we have considered such compression in the setting of a giant aneurysm an indication for open surgical decompression.
In truth, an entire book could be written focusing on the management of giant aneurysms. In most cases, simple neck clipping will not be feasible. When attempting direct clipping, the thick necks of these aneurysms will often preclude simple clips from closing. The surgeon must be very careful to avoid creating a tear at the junction of the neck with the parent artery or an efferent branch as a large heavy clip attempts to force shut a thickened neck that resists closure. Although surgical exploration for possible clipping is often worthwhile, the surgeon should have a well-measured plan of attack that assumes attempted primary clip reconstruction may be unsuccessful.
When evaluating giant aneurysms, several points should always be considered. These include: patient age and comorbidities, the presence or absence of symptomatic mass effect, degree of calcification and atheroma at the aneurysm neck based on cross-sectional imaging, incorporation of efferent branches into the aneurysm neck, likely tolerance of temporary or permanent occlusion, possible role of bypass, size of the superficial temporal artery (STA) and occipital artery, and potential tolerance of deep hypothermic arrest.
Despite the inherent challenges, some giant aneurysms can be clipped primarily, and surgical exploration to attempt primary clipping represents a reasonable approach in selected cases ( Figs. 9.1, 9.2 ). Adjunctive techniques that we have found useful or essential in these cases include the liberal use of temporary clips, suction decompression, deep hypothermic circulatory arrest, and preliminary bypass to allow for prolonged temporary occlusion.
The first video in this chapter demonstrates the treatment of a giant ruptured paraclinoid aneurysm repaired using multiple fenestrated clips to reconstruct the internal carotid artery (ICA) during a short period of temporary occlusion . If the aneurysm in this case had not softened considerably with simple temporary clipping, then suction decompression could have been utilized.
In some cases, it appears that the aneurysm will be clippable, but only with a period of prolonged temporary occlusion that will likely exceed the patient’s tolerance for such occlusion. In these instances, we have utilized either deep hypothermic circulatory arrest or preliminary bypass to enable the prolonged occlusion.
In the most experienced of hands, deep hypothermic circulatory arrest procedures carry significant morbidity and mortality, exceeding 10% for the systemic complications relating to the cardiac procedure alone. Nevertheless, in selected instances, circulatory arrest will allow the surgeon the time necessary to properly dissect and clip a giant aneurysm. The cardiac surgeon can provide a “low-flow state” during which the preliminary dissection can be completed, leaving only the final critical stages of the dissection and clipping for the true arrest period. The arrest can be performed using either a closed- or open-chest technique, and periods of arrest exceeding one hour have been utilized safely and successfully. Nevertheless, we have preferred to keep the arrest period under 45 minutes whenever possible.
When performing an arrest procedure, the craniotomy opening should be meticulous in terms of hemostasis, as the patient will be fully anticoagulated for a prolonged period and the hypothermia will further compromise clotting. It is quite amazing to watch complete cessation of blood flow to the brain. As pulsation stops, the intracranial circulation empties, allowing for aggressive dissection of the aneurysm. Once the aneurysm has been clipped, the neurosurgeon must wait during the rewarming process prior to closing the craniotomy. Only when the heparin has been fully reversed and normal coagulation has been restored can the craniotomy be closed. We have included one example of a deep hypothermic circulatory arrest for a giant ruptured anterior communicating artery (ACommA) aneurysm with severe subarachnoid hemorrhage (SAH) ( Fig. 9.3 ).
To illustrate the use of preliminary bypass to enable prolonged temporary occlusion, we have included an example of a giant carotid ophthalmic aneurysm managed in this fashion, using a superficial temporal artery to middle cerebral artery (STA-MCA) bypass ( Fig. 9.4 ). The advantage of this technique includes the possibility of using permanent occlusion as a treatment option if the aneurysm cannot be primarily reconstructed. Nevertheless, the bypass takes time at the beginning of an already challenging procedure, and this must be weighed when considering the various treatment options.
When a giant aneurysm cannot be clipped primarily, we have found the use of various bypass techniques to be incredibly helpful in managing even the most complex of giant aneurysms. Multiple examples of such cases are included in the next section.