**5.5 Arachnoidal dissection**

Although sometimes difficult due to extensive adhesions, this step is mandatory for exploring the optochiasmatic region. The opening in the Sylvian valley is made just above the ipsilateral optic nerve, the most constant landmark and the place where the arachnoid is the furthest from the cortex. Next, the opening is extended both laterally and medially using a thin aspirator and microsurgical scissors. Evacuation of the CSF will further relax the brain and offer a large operating field. Dissection resumes medially for ACoA aneurysms and laterally for PCoA aneurysms, whereas it continues along the artery itself for internal carotid artery lesions. Once the valley has been opened, the bifurcation of the ICA is visible, and the neck of the aneurysm can be distinguished. The neck is then dissected and isolated from the surrounding normal vasculature. For middle cerebral artery aneurysms, the ICA should be dissected laterally, as well as the proximal portion of the MCA. This type of opening has some drawbacks, as it first brings the surgeon to the tip of the aneurysmal sac and the proximal control is lacking at this moment. But a delicate dissection proximal to the aneurysm will shortly offer the visibility over the M1 segment, where a temporary clip could be safely placed. The interoptic triangle allows access toward basilar apex aneurysms; however, accessing the neck of the aneurysm itself is much more challenging, especially since the first element that "greets" the surgeon in this approach is the aneurysmal fundus.

The parent vessel has to be exposed proximally to the aneurysm to ensure blood flow control in the case of intraoperative rupture. The main vessel should be adequately exposed before the neck of the aneurysm, which, in turn, should be dissected before the fundus. The perforators adjacent to the lesion must be separated from the neck before placing the permanent clip. If the aneurysm sac is too wide and complex to be clipped, prudent use of the bipolar coagulator can adjust its diameter. Immediately after the clip is placed, the permeability of surrounding vessels and perforators must be demonstrated. If intraoperative rupture occurs, lowering arterial pressure, tamponing, temporary clipping of parent vessel, and aspirating the aneurysmal sac will favor neck definition and placement of definitive clip.

#### **5.6 Clipping**

Once the aneurysm has been successfully dissected from the surrounding vessels, a permanent clip is placed at the aneurysmal neck. It has to be parallel to the parent artery in order to avoid stretching or occluding it. The length and shape of the clip should be adapted to the morphology of the aneurysm and must trap the neck entirely, without also trapping perforators or adjacent structures. Sometimes, it is necessary to reduce the volume of the aneurysm by applying a temporary clip proximal to the aneurysm. Timing in this step is crucial, as more than 10 min of temporary occlusion of a major vessel such as the MCA or ICA can lead to severe consequences. Once the aneurysm has shrunk enough, the permanent clip can be carefully applied (**Figure 2**).

#### **5.7 Intraoperative aneurysmal rupture (IAR)**

This is a dreadful but preventable incident, more hazardous if it occurs early, such as during induction of anesthesia or while opening of the dura. Arguably

**155**

as early as possible.

**5.9 Postoperative control**

**5.8 Closure**

**Figure 2.**

*author of this chapter).*

*Preventing Rupture: Clipping of Unruptured Intracranial Aneurysms*

the most challenging of IARs may be those of basilar apex aneurysms. The aims in this scenario are hemostasis, avoiding further aneurysmal damage, preventing accidental injury to main vessels and perforators, and, finally, clipping the aneurysm. Certain steps should be followed to avoid IAR: careful positioning of the head to minimize brain traction; vigilant induction of anesthesia and ensuring that hypertension bouts do not occur; a sufficiently wide craniotomy that guarantees appropriate access, as well as adequate brain relaxation (using diuretics or a preoperative lumbar drainage); and last but not least, sharp instruments are safer for dissection than blunt instruments. Ensuring proximal control before aneurysmal neck dissection can diminish the risk of IAR. Also, using the anatomical paths through the arachnoidal planes will also lower the chance of IAR. In our practice, we apply temporary clips if we anticipate a difficult dissection, for example, giant aneurysms, polylobulated aneurysms, or those that have recently bled. Even so, the occlusion via temporary clip should not exceed a cumulative 20–25 min with repeated placements. However, temporary clips are the most useful in IAR if placed

*Representation of an unruptured aneurysm before (A) and after clipping (B) (drawings provided by the first* 

Without exception, this is performed after thorough hemostasis. For this, we employ hemostatic materials (Surgicel® or Gelfoam®) and the judicious use of the bipolar coagulator. Patience is essential, as rushing this step can compromise the entire operation. In nearly all our surgeries, we use autologous periosteum to perform dural plasty. In our opinion, near-watertight closure of the dura with a 5/0 thread (either with continuous or separate sutures) is sufficient. The bone is inserted back into place and fixed either with titanium mesh and screws or sutures with thick threads passing through small burr holes. Placing an external drainage under the aponeurosis for a period of 24 h is mandatory. The skin closure is per-

We usually perform a CTA after closure, with the patient still sedated and intubated. It is much safer to make sure that the vessels are angiographically permeable, or to correct any abnormality under the same anesthesia, than to wait for the patient to awake and develop ischemic complications. We have also used intraoperative

formed either continuously or with separate sutures or staples.

*DOI: http://dx.doi.org/10.5772/intechopen.88038*

*Preventing Rupture: Clipping of Unruptured Intracranial Aneurysms DOI: http://dx.doi.org/10.5772/intechopen.88038*

**Figure 2.**

*New Insight into Cerebrovascular Diseases - An Updated Comprehensive Review*

left in place to protect the brain.

surgeon in this approach is the aneurysmal fundus.

**5.5 Arachnoidal dissection**

suspending the dural flap, we ensure a wide enough opening. The rest of the dura is

Although sometimes difficult due to extensive adhesions, this step is mandatory for exploring the optochiasmatic region. The opening in the Sylvian valley is made just above the ipsilateral optic nerve, the most constant landmark and the place where the arachnoid is the furthest from the cortex. Next, the opening is extended both laterally and medially using a thin aspirator and microsurgical scissors. Evacuation of the CSF will further relax the brain and offer a large operating field. Dissection resumes medially for ACoA aneurysms and laterally for PCoA aneurysms, whereas it continues along the artery itself for internal carotid artery lesions. Once the valley has been opened, the bifurcation of the ICA is visible, and the neck of the aneurysm can be distinguished. The neck is then dissected and isolated from the surrounding normal vasculature. For middle cerebral artery aneurysms, the ICA should be dissected laterally, as well as the proximal portion of the MCA. This type of opening has some drawbacks, as it first brings the surgeon to the tip of the aneurysmal sac and the proximal control is lacking at this moment. But a delicate dissection proximal to the aneurysm will shortly offer the visibility over the M1 segment, where a temporary clip could be safely placed. The interoptic triangle allows access toward basilar apex aneurysms; however, accessing the neck of the aneurysm itself is much more challenging, especially since the first element that "greets" the

The parent vessel has to be exposed proximally to the aneurysm to ensure blood flow control in the case of intraoperative rupture. The main vessel should be adequately exposed before the neck of the aneurysm, which, in turn, should be dissected before the fundus. The perforators adjacent to the lesion must be separated from the neck before placing the permanent clip. If the aneurysm sac is too wide and complex to be clipped, prudent use of the bipolar coagulator can adjust its diameter. Immediately after the clip is placed, the permeability of surrounding vessels and perforators must be demonstrated. If intraoperative rupture occurs, lowering arterial pressure, tamponing, temporary clipping of parent vessel, and aspirating the aneurysmal sac will favor neck definition and placement of

Once the aneurysm has been successfully dissected from the surrounding vessels, a permanent clip is placed at the aneurysmal neck. It has to be parallel to the parent artery in order to avoid stretching or occluding it. The length and shape of the clip should be adapted to the morphology of the aneurysm and must trap the neck entirely, without also trapping perforators or adjacent structures. Sometimes, it is necessary to reduce the volume of the aneurysm by applying a temporary clip proximal to the aneurysm. Timing in this step is crucial, as more than 10 min of temporary occlusion of a major vessel such as the MCA or ICA can lead to severe consequences. Once the aneurysm has shrunk enough, the permanent clip can be

This is a dreadful but preventable incident, more hazardous if it occurs early, such as during induction of anesthesia or while opening of the dura. Arguably

**154**

definitive clip.

**5.6 Clipping**

carefully applied (**Figure 2**).

**5.7 Intraoperative aneurysmal rupture (IAR)**

*Representation of an unruptured aneurysm before (A) and after clipping (B) (drawings provided by the first author of this chapter).*

the most challenging of IARs may be those of basilar apex aneurysms. The aims in this scenario are hemostasis, avoiding further aneurysmal damage, preventing accidental injury to main vessels and perforators, and, finally, clipping the aneurysm. Certain steps should be followed to avoid IAR: careful positioning of the head to minimize brain traction; vigilant induction of anesthesia and ensuring that hypertension bouts do not occur; a sufficiently wide craniotomy that guarantees appropriate access, as well as adequate brain relaxation (using diuretics or a preoperative lumbar drainage); and last but not least, sharp instruments are safer for dissection than blunt instruments. Ensuring proximal control before aneurysmal neck dissection can diminish the risk of IAR. Also, using the anatomical paths through the arachnoidal planes will also lower the chance of IAR. In our practice, we apply temporary clips if we anticipate a difficult dissection, for example, giant aneurysms, polylobulated aneurysms, or those that have recently bled. Even so, the occlusion via temporary clip should not exceed a cumulative 20–25 min with repeated placements. However, temporary clips are the most useful in IAR if placed as early as possible.

#### **5.8 Closure**

Without exception, this is performed after thorough hemostasis. For this, we employ hemostatic materials (Surgicel® or Gelfoam®) and the judicious use of the bipolar coagulator. Patience is essential, as rushing this step can compromise the entire operation. In nearly all our surgeries, we use autologous periosteum to perform dural plasty. In our opinion, near-watertight closure of the dura with a 5/0 thread (either with continuous or separate sutures) is sufficient. The bone is inserted back into place and fixed either with titanium mesh and screws or sutures with thick threads passing through small burr holes. Placing an external drainage under the aponeurosis for a period of 24 h is mandatory. The skin closure is performed either continuously or with separate sutures or staples.

## **5.9 Postoperative control**

We usually perform a CTA after closure, with the patient still sedated and intubated. It is much safer to make sure that the vessels are angiographically permeable, or to correct any abnormality under the same anesthesia, than to wait for the patient to awake and develop ischemic complications. We have also used intraoperative

fluorescence angiography to not only verify the occlusion of the aneurysmal sack but also the patency of the surrounding normal vessels.

## **6. Hemodynamic consequences of aneurysm clipping**

The hemodynamic characteristics of intracranial aneurysms are thought to play a pivotal role in their development, evolution, and eventual rupture, interfering and modifying the local biology of the vascular wall [61–63]. The theory suggests that the wall is exposed to a higher degree of sheer stress than it can physiologically withstand. This leads to a local weakening and abnormal remodeling, which in time will form an aneurysm. Its growth can be a result of local proliferation of mural cells, a distention of the cellular and intercellular structures, or possibly a mixture of the two. A meticulous in vitro study affirmed that growth cannot be entirely the result of simple fluid physics [64], a non-Newtonian model being more precise in ascertaining the altered hemodynamics in intracranial aneurysms [65]. However, as it is impossible to perform direct measurements on hemodynamic stress in patients or living experimental models, methods implying computational fluid dynamics are used to estimate these phenomena [65–67].

Aneurysmal rupture results from the mechanical weakening of the arterial wall that is subsequently unable to contain the force of the flowing blood [68]. The wall sheer stress is defined as the tangential frictional force that the blood exerts upon the endothelium, being the highest at the neck and the apex of the aneurysm [65]. The innerworkings of endovascular procedures are closely linked to these hemodynamic conditions, as the presence of a coil determines alterations in wall shear stress and blood flow that conclude with the intraluminal thrombosis of the aneurysm [69]. In MIA, wall sheer stress is apparently increased in UIAs distal to a ruptured aneurysm after treatment, whether surgical or endovascular, leading to a theoretical rise in the risk of rupture [66]. Moreover, also in MIA, ruptured aneurysms may possess a more irregular shape, larger size, and dometo-neck ratio, as well as a lower minimum wall shear stress than with their unruptured counterparts [70].

After clipping, a series of local and distal changes in hemodynamics may occur. Nevertheless, these are not as intensely analyzed as for untreated aneurysms. Successful surgical obliteration of the aneurysm results in the complete cessation of blood flow inside the lumen. However, it is not clear what impact the presence of the aneurysmal clip itself has on the wall shear stress or its effects on the vascular wall. A residual neck (i.e., a portion of the neck that was not occluded by the blades of the clip) may in time lead to aneurysmal regrowth, depending on the size of the remnant as well as its location [71]. Apparently, a distal remnant is at a higher risk for aneurysmal regrowth than a proximal residue. Therefore, it is crucial to ensure an adequate placement of the clip during surgery and to adjust its position if required. The alterations in dynamic flow can also be observed systemically after clipping or coiling, especially in the period after vasospasm caused by aneurysmal rupture [72]. In the study conducted by Inoue et al., patients treated by coiling presented a significantly lower cardiac index, as well as a significantly higher systemic vascular resistance index than the group managed via clipping, although this might have been the result of systemic therapy for managing vasospasm and aggressive volume loading rather than of the procedure itself, especially as the patients in the coiling group arrived in a worse neurological state than those of the clipping group. Needless to say, more studies are required to discern the actual impact that clipping has on the cerebral vasculature, especially concerning aneurysmal regrowth, reoccurrence, and rerupture.

**157**

UIAs [79].

*Preventing Rupture: Clipping of Unruptured Intracranial Aneurysms*

The cerebrovascular diseases causing such controversy in regard to treatment are few in number [73]. The reasoning behind this continuous debate is that the prophylactic management of UIAs must be justified by a suitable procedurerelated outcome when compared to the anticipated natural history [74]. Despite clipping once being the management centerpiece, the swift refinement of endovascular procedures and innovation of flow diversion devices have steadily replaced surgery as the first line of therapy for UIAs. However, certain countries still favor clipping due to its longevity, effectiveness, and the lower risk of recanalization than endovascular techniques, as well as lower procedure-related costs [75–77]. Consequently, whereas older patients who are unsuitable for surgery may benefit the most from endovascular procedures, clipping is considered preferable for younger patients with lower-grade aneurysms and that may be able to tolerate this intervention [76, 78]. The unruptured intracranial aneurysm treatment score (UIATS) provides a fast and easy method of triaging between the two treatment options; however, it has not yet been prospectively tested on patients harboring

Studies such as ISAT, ISUIA, and UCAS are among the most cited concerning aneurysm treatment and natural history. The first of these revealed superior 1-year clinical outcomes for ruptured aneurysms by coiling in comparison to clipping, yet these results cannot be accurately extrapolated to clipping of UIAs [80]. The conditions in the unruptured setting are more advantageous, as the purpose of therapy is to ensure lifelong protection against aneurysm rupture, whereas the treatment of ruptured lesions is to allow survival of the patient during the acute phase of SAH without rebleeding or postoperative morbidity. Likewise, MCA aneurysms, which are generally considered more easily approached by surgery, were grossly underrepresented in this study. Several authors obtained much higher rates of complete obliteration via clipping than through endovascular procedures for aneurysms in this location [77, 81, 82]. This is more likely a consequence of the particular configurations of MCA aneurysms, rendering it more difficult to completely occlude the neck via endovascular procedures (wide-necked, possessing a small dome-to-neck ratio, the neck encompassing one of the arterial branches, etc.) [77]. Moreover, these aneurysms are generally adjacent to or surrounded by small perforators that may prohibit the use of stents. This technique also has the fundamental drawback of postprocedural thromboembolic events that may ensue at a higher frequency [83, 84]. In the largest multicenter study of very small UIAs treated via surgery, Bruneau et al. showed that the lesions found distal to the M1 segment were the safest to treat [85]. Despite additional enquires being required to reach a definitive conclusion, it is still worth regarding surgical clipping as the principal treatment modality for UIAs of the MCA.

Aneurysms of the anterior communicating artery are the most frequently reported in a large number of studies, possessing a higher risk of rupture than other locations while also being amenable to both endovascular and microsurgical techniques [36, 74, 86–89]. The term may actually be overly broad, also including aneurysms of the A1 and A2 junctions of the anterior cerebral artery or belonging entirely to these two segments, but being indistinguishable from true ACoA aneurysms on angiographic studies [88]. This location represents a genuine challenge for either approach. On the one hand, microvascular clipping is made difficult by depth, presence of perforators, and placement along the midline, implying increased cerebral traction in the absence of adequate relaxation [87, 89]. On the other hand, certain intrinsically unfavorable characteristics of aneurysms found in this location, such as a small dome, wide neck, multiple adjacent perforators, acute vessel angles, complex morphology, or posterior projection, can hinder

**7. Clipping of solitary unruptured aneurysms**

*DOI: http://dx.doi.org/10.5772/intechopen.88038*
