Aneurysms

Microsurgery

Surgical treatment of intracranial aneurysms originated in the 1930s, prior to which the treatment of choice was hunterian ligation of the parent vessel. The morbidity and mortality were quite high before the advent of the operating microscope. Refinement of microscopic technology and development of micro-surgical techniques have established clip ligation as a time-honored, durable, and standard treatment for intracranial aneurysms. A thorough knowledge of the cisternal and vascular anatomy and microsurgical navigation through the cisterns, with egress of cerebrospinal fluid (CSF) affording brain relaxation, has established surgical clip ligation as a minimally invasive, low-risk, and efficacious treatment option for these lesions. The pterional approach, described by Yasargil and Fox (3), is the most widely used approach compared with bifrontal and frontolateral craniotomies for access to the anterior circulation. A criticism of this approach has been the limited resection of the gyrus rectus necessary for exposure and control of the anterior communicating (ACOM) artery complex despite the lack of evidence of adverse neurological sequelae. Also, the cosmetic results from a standard pterional approach can be disturbing owing to temporalis muscle atrophy. This has given impetus to the development of minimally invasive surgical techniques (4-6).

The goal of microsurgical techniques developed during the last few decades has been to reduce iatrogenic trauma and improve postoperative outcomes. This has been enhanced by the increased sophistication of microscopes, neuronavigation systems, stereotactic techniques, and intraoperative endoscopes. Concomitantly, there has been an evolution of diagnostic and preoperative imaging techniques allowing precise localization of lesions and providing exquisite anatomic details for operative planning. These developments have led to the keyhole concept of microneurosurgery.

A transorbital keyhole approach to ACOM artery aneurysms has recently been described (7). The rationale behind this technique is to render the dissection of the ACOM complex completely extracerebral, obviating the need for or minimizing the gyrus rectus resection. Also, temporalis muscle dissection is minimized. The eyebrow keyhole approach is another attempt at reducing the invasiveness of standard microsurgery (8). The skin incision is made in the lateral two-thirds of the eyebrow, followed by a small supraorbital craniotomy. This is especially useful cosmetically in people with receding hairlines. Paladino et al. (8) used this approach with an endoscope to visualize the neck better to treat 37 patients with 40 intracranial aneurysms with no mortality and excellent cosmetic results.

The disadvantages of the keyhole approach are the narrow viewing angles, limited space for manipulating microinstruments, and reduced operating field light intensity. One method of improving the light intensity with keyhole cran-iotomies is the use of endoscopes. The first endoscopic neurosurgical procedure was performed in 1910 to cauterize the choroid plexus in hydrocephalic infants (9). Since then, endoscopic technology has undergone major advances (10,11). The introduction of the rigid rod lens scope has revived interest in neuroen-doscopy. There are a growing number of applications for treating lesions in the intraventricular and subarachnoid spaces. Recently, Kalavakonda et al. (12) described the use of an endoscope in assisting microsurgery for aneurysms in 55 patients with 79 aneurysms. The endoscope reportedly provides additional views not available with a standard microscope. In 26 aneurysms, the authors reported that endoscopic assistance provided a better view than would have been possible with the microscope alone. However, in more than half the cases, the endoscope did not seem to provide useful information.

The use of navigation systems in aneurysm surgery is limited. 3D subtraction angiography and 3D computed tomographic angiography (CTA) are emerging technologies that may be useful for preoperative planning in patients with intracranial aneurysms (13,14). However, their use in determining the size and placement of craniotomies is limited. In our experience, these advances have been more useful in determining the viability of endovascular options and more often in revealing anatomic details that suggest surgical clip ligation may be better suited for a particular aneurysm.

It has been suggested that keyhole microneurosurgery may contribute to improved postoperative results through shorter hospitalization times by reducing complications such as bleeding, infection, CSF leak, and neurological deterioration with brain retraction (8). Although it certainly is a useful addition to the armamentarium for microsurgery, its routine use is not recommended. Simplicity and cosmetic results are important in craniotomies, but it should not be at the expense of safety and efficacy.

Endovascular Treatment

Endovascular treatment of intracranial aneurysms began in the 1960s and 1970s. Serbinenko (1), with the creation of a latex detachable balloon for endovascular obliteration, is arguably the father of endovascular therapy. In 1981, Debrun et al. (2) used detachable balloons for parent vessel occlusion in patients with giant aneurysms and began the North American experience. Subsequently balloon occlusion of aneurysms was replaced by coil embolization. Guido Guglielmi invented detachable coils, which revolutionized the endovas-cular treatment of aneurysms through the development of Guglielmi detachable coils (GDCs; Boston Scientific/Target Therapeutics, Fremont, CA) (15). The major advantage of this system is the softness and compliance of the coil, allowing packing of the aneurysm dome. Other benefits include controlled delivery and retrievability. However, the GDC technique has some limitations. Large and giant aneurysms, as well as wide-necked and complex aneurysms, are difficult to pack densely with this technique. This led to the development of adjuncts to coiling, such as balloon remodeling (16) and stenting (17-20). In the remodeling technique, the balloon not only functions as an external barrier and prevents coils from escaping into the parent artery, but also allows for tighter packing of the dome with coils. The development of new flexible, intravascular stents has further improved the density of packing. Stents function as scaffolds, preventing the coils from escaping into the parent vessel. (Fig. 1) The safety and efficacy of this technique have been reported recently (17-21). Recently, the Neuroform microdelivery stent system (SMART Therapeutics, San Leandro, CA) has been approved for use with embolic coils specifically for the treatment of wide-necked saccular aneurysms. Its efficacy remains to be established.

Endovascular therapy has generated not only great enthusiasm but also great controversy because of its potential therapeutic benefits vs lack of long-term data to establish its durability. The International Subarachnoid Aneurysm Trial Collaborative Group (ISAT) reported the results of its randomized trial of coiling vs clipping of intracranial aneurysms (22). In this study, 9559 patients with subarachnoid hemorrhage (SAH) were seen in multiple centers. Of these, 7416 patients were excluded form the study and 2143 were randomized. At the end of 1 yr, 190 of 801 patients (23.7%) allocated to endovascular treatment were dependent or dead compared with 243 of 793 (30.6%) allocated to surgery. The relative risk reduction was 22.6%, with an absolute risk reduction of 6.9%. The conclusions reached from the trial's data were that endovascular coiling is significantly more likely to result in survival free of disability 1 yr after SAH than neurosurgical treatment. Longer term follow-up, however, is vital to answer the question of durability of benefit (22).

This study has come under criticism for a number of reasons, including selection bias, the large number of patients who were not randomized, short follow-up, and subjective outcome assessment. The overwhelming majority of patients randomized had small aneurysms (93%) on the anterior circulation (97.3%) and were good grade (88%) (22). Outcomes after aneurysm treatment should be determined by the rate of periprocedural complications and the success in the reduction of rebleeding. One of the great drawbacks of endovascular therapy with the current technology is the incomplete obliteration of the dome of the aneurysm which can directly result in increased rebleeding rates. Therefore, a

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