Minimally Invasive Microsurgery for Cerebral Aneurysms
2015; Lippincott Williams & Wilkins; Volume: 46; Issue: 9 Linguagem: Inglês
10.1161/strokeaha.115.008221
ISSN1524-4628
AutoresJohnny Wong, Rachel Tymianski, Ivan Radovanovic, Michael Tymianski,
Tópico(s)Traumatic Brain Injury and Neurovascular Disturbances
ResumoHomeStrokeVol. 46, No. 9Minimally Invasive Microsurgery for Cerebral Aneurysms Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBMinimally Invasive Microsurgery for Cerebral Aneurysms Johnny Ho Yin Wong, PhD, Rachel Tymianski, Ivan Radovanovic, PhD and Michael Tymianski, MD, PhD Johnny Ho Yin WongJohnny Ho Yin Wong From the Division of Neurosurgery, Toronto Western Hospital, University Health Network, Toronto, Ontario, Canada (J.H.Y.W., R.T., I.R., M.T.); and Department of Surgery, University of Toronto, Toronto, Ontario, Canada (J.H.Y.W., I.R., M.T.). , Rachel TymianskiRachel Tymianski From the Division of Neurosurgery, Toronto Western Hospital, University Health Network, Toronto, Ontario, Canada (J.H.Y.W., R.T., I.R., M.T.); and Department of Surgery, University of Toronto, Toronto, Ontario, Canada (J.H.Y.W., I.R., M.T.). , Ivan RadovanovicIvan Radovanovic From the Division of Neurosurgery, Toronto Western Hospital, University Health Network, Toronto, Ontario, Canada (J.H.Y.W., R.T., I.R., M.T.); and Department of Surgery, University of Toronto, Toronto, Ontario, Canada (J.H.Y.W., I.R., M.T.). and Michael TymianskiMichael Tymianski From the Division of Neurosurgery, Toronto Western Hospital, University Health Network, Toronto, Ontario, Canada (J.H.Y.W., R.T., I.R., M.T.); and Department of Surgery, University of Toronto, Toronto, Ontario, Canada (J.H.Y.W., I.R., M.T.). Originally published30 Jul 2015https://doi.org/10.1161/STROKEAHA.115.008221Stroke. 2015;46:2699–2706Other version(s) of this articleYou are viewing the most recent version of this article. Previous versions: January 1, 2015: Previous Version 1 Intracranial aneurysms arise in ≈2% of the population, and their rupture causes 3% of all strokes.1 Their treatment requires safely achieving complete aneurysm occlusion while preserving blood flow in the parent, branching, and perforating vessels. For decades, this task was achieved using classic open approaches, such as the pterional craniotomy (PTC) described by Yasargil and Fox in 1975, which afforded safe and effective exposure of the Circle of Willis through the Sylvian fissure with minimal retraction on the frontal and temporal lobes.2 Supported by the introduction of the operating microscope, this approach gained popularity for treating tumors and aneurysms of the anterior circulation and the basilar tip.2–4However, the most significant advance in aneurysm treatment has been the advent of safe and effective endovascular techniques for the treatment of intracranial aneurysms, buoyed by clinical trials, such as International Subarachnoid Aneurysm Trial5 and Barrow Ruptured Aneurysm Trial (BRAT).6 Although both surgical and endovascular aneurysm occlusion technologies are effective for appropriately selected patients, endovascular treatment is also perceived to be less invasive as compared with classical open surgery. Indeed, technological developments in microsurgery, such as improved vascular imaging, intraoperative navigation, and fluorescence angiography,7 have focused on improving precision and effectiveness. However, more recently, the advent of endovascular techniques has spurred a shift of surgery to minimally invasive techniques with the goal of improving tolerability, cosmesis, and acceptability for patients. Ideally, this should translate to equivalent safety and efficacy as surgery through standard craniotomies, but with the benefit of reduced operative time, postoperative pain, and length of in-hospital stay and improved cosmesis.4,8 This article reviews the evolution of minimally invasive microsurgery (MIM) with keyhole or mini-craniotomies and the development of endoscope-assisted and purely endoscopic aneurysm surgery. These techniques are already well established in skull base neurosurgery, but are only now being increasingly applied to aneurysm operations.Classic Pterional CraniotomyAneurysm surgery requires exposure and adequate visualization of the circle of Willis at the skull base. Initially, surgeons used the frontolateral craniotomy as described by Dandy in 1938, involving extensive retraction of the frontal and temporal lobes to provide visualization of an aneurysm.9 With the advent of the improved illumination and magnification afforded by operating microscopes, Yasargil promoted the PTC involving less brain retraction but more bone removal of the sphenoid wing and dissection of the Sylvian fissure.2 This approach requires a long skin incision hidden behind the hairline, significant dissection and disruption of the temporalis muscle, and a craniotomy involving the frontal, squamous temporal, and greater wing of sphenoid bones with drilling of the sphenoid wing. The PTC gives access to the optic apparatus and the Circle of Willis once the Sylvian fissure is split.2,10 However, the extensive surgical manipulation and retraction of the temporalis muscle causes it delayed atrophy and scarring, producing facial asymmetry, discomfort with eyewear, and risks temporomandibular joint dysfunction, mastication pain, and injury to the frontal branch of the facial nerve.4 In addition, large areas of cerebral cortex are unnecessarily exposed. These factors contribute adversely to length of hospitalization and return to employment and activities of daily living.Pterional Variations: Keyhole or Mini-CraniotomiesTo address such drawbacks, several miniature versions, termed keyhole or mini-craniotomies, have been developed. These include supraorbital (SOC), lateral supraorbital (LSOC), mini-pterional (MPTC), and interhemispheric craniotomies (Figure 1). In essence, most are modeled on the PTC, but customize the opening location, trajectory, angle of approach, and extent of exposure to the exact position of the aneurysm, thereby minimizing unnecessary temporalis dissection and brain exposure (Table 1).Table 1. Comparison of Pterional and Mini-Craniotomy ApproachesClassic Pterional (PTC)Supraorbital (SOC)Lateral Supraorbital (LSOC)Mini-Pterional (MPTC)Skin incisionBehind hairline: beginning at root of zygoma (<1 cm from tragus) past midlineEye-brow; or behind hairline: beginning at 2 cm above zygomatic arch and to midlineBehind hairline: beginning at 2 cm above zygomatic arch to midpupillary lineBehind hairline: beginning at 2 cm above zygomatic arch and midpupillary lineTemporalis dissectionInterfascial; temporalis completely disconnectedInterfascial; minimal temporalis dissection anteriorlyMyocutaneous; temporalis incised superoanteriorlyInterfascial or myocutaneous; temporalis incised superoanteriorlyCraniotomy (location)Frontal, pterion squamous temporal bonesBetween supraorbital notch and frontozygomatic sutureBetween lateral orbital rim, greater sphenoid wing, and superior temporal lineSuperior temporal line, pterion, and squamous temporalCraniotomy (size)6×6 cm2.5×1.5 cm3×2.5 cm4×3 cmCraniotomy (sphenoid drilling)To superior orbital fissureNot requiredNot requiredTo superior orbital fissureBrain (cortical exposure)Frontal, temporal lobes, and Sylvian fissureFrontal pole and orbital gyriInferior frontal gyrus, edge of Sylvian fissureInferior frontal and superior temporal gyrus, Sylvian fissureSylvian fissure openingYesOptionalOptionalYesSurgical corridorMultiple corridorsSubfrontalSubfrontalTrans-sylvian/lateralSuitable aneurysms: well visualizedOphthalmic ICA, PComA, AChoroidalA, terminal ICA, MCA, AComAAComA, MCA, PComAAComA, MCA, PComA, AChoroidalA,MCA, terminal ICA, ophthalmic ICAAComA indicates anterior communicating artery; ICA, internal carotid artery; MCA, middle cerebral artery; and PComA, posterior communicating artery.Download figureDownload PowerPointFigure 1. Illustration of the most common keyhole craniotomies as compared with the standard pterional craniotomy.Supraorbital CraniotomyThe SOC was first described for aneurysms by Paladino et al and Van Lindert et al in 1998.11,12 An example is illustrated in Figure 2. It is a subfrontal approach to the anterior skull base giving access to both supratentorial and basilar aneurysms.13–15 It is performed either through an incision behind the hairline superficial to the temporalis fascia or an eyebrow or transciliary incision, preserving the supraorbital nerve and the nerve to frontalis. The craniotomy is as small as 25×15 mm, but gives an ample trajectory to the basal cisterns, lamina terminalis, and most midline and paramedian aneurysms.7,13 Specific risks include a frontal sinus breach with cerebrospinal fluid leakage and palsies of supraorbital and facial nerves with associated forehead numbness and weakness, respectively.Download figureDownload PowerPointFigure 2. Subfrontal minicraniotomy for exposing and clipping an anterior-communicating artery aneurysm. A, Typical bony opening. B, Exposure of the optic apparatus and contralateral A1 and A-com arteries. C, Exposure of the aneurysm neck. D, Clipping of the aneurysm.Lateral Supraorbital CraniotomyHernesniemi et al16 developed the LSOC approach through which he performed thousands of operations for anterior circulation aneurysms and tumors of the anterior fossa and sellar regions. Compared with SOC, it is a more posteriorly located skull opening with a less subfrontal angle involving a comparatively shorter incision behind the hairline and minimal temporalis dissection. It is typically ≈3×3cm in size, much smaller than the PTC, but gives access to the Sylvian fissure, basal cisterns, lamina terminalis, and the circle of Willis.16,17 LSOC limits access to the distal Sylvian fissure and retraction of the temporal lobe, which may be problematic with brain swelling or intracerebral hematoma.18Mini-Pterional CraniotomyThis approach was originally termed the sphenoid ridge keyhole craniotomy by Nathal et al, but Figueiredo et al later termed the technique mini-pterional.4,19 It involves an opening that essentially replicates the sphenoid-wing drilling of the PTC, but with a much reduced frontal and temporal bony opening and minimal disruption of the temporalis muscle, making some MPTCs as small as 2×1.5 cm. The skin incision is also short, similar to the LSCO. The MPTC provides access to the inferior frontal and superior temporal gyri, the Sylvian fissure dissection to the anterior ascendant ramus, and the aneurysms of the carotid and middle cerebral arteries.4,20 Limitations include restricted access to the distal Sylvian fissure, especially in the case of brain swelling or hemorrhage.18Interhemispheric CraniotomyFukushima et al21 described an anterior midline keyhole craniotomy for an interhemispheric approach in 1991 for aneurysms involving anterior cerebral artery (ACA), including anterior communicating artery (AComA) aneurysms. Although this is not a variation of the PTC, it may be suitable for high projecting AComA and distal ACA aneurysm.17Feasibility and Appropriateness of Different MIM ApproachesThe main criticisms of MIM surgery have been concerns that limitations of exposure and freedom to manipulate instruments could compromise patient safety. To address this, Figueiredo et al used cadaveric specimens to quantify the area of surgical exposure and the angular exposure in both the MPTC and PTC.4 The area of surgical exposure consisted of the most distal points exposed along the sphenoidal ridge, middle cerebral artery (MCA) and posterior cerebral artery bilaterally, and represented the working space available under the microscope, whereas the maximum angular exposure was calculated for the ipsilateral internal carotid artery (ICA), MCA, and AComA as targets, which represented the multiple directions and surgical avenues available. The results did not demonstrate any significant difference in the area nor angle of exposure between the 2 approaches.Similar conclusions were reached by Yeremeyeva et al who compared the exposure and surgical maneuverability around structures near the AComA complex between SOC, LSOC, and MPTC.22 All 3 craniotomies offered good visualization and potential for surgical manipulation of the specific arterial locations to which the approach was targeted. They noted that the views and maneuverability from all approaches were enhanced by adding an endoscope, particularly views of the contralateral structures. Kang et al compared the size and working angles with AComA, MCA bifurcation, and terminal ICA as targets in SOC and MPTC.23 Based on CT scans of 13 patients after aneurysm clipping, there was a significantly larger area of exposure and range of operating angles offered by MPTC than SOC, particularly for MCA bifurcation. SOC has a straighter trajectory to AComA, but has a greater distance to ICA terminus and MCA bifurcation than MPTC.23Overall, MPTC is most suited for aneurysms requiring a full Sylvian fissure split, for example, MCA, ICA bifurcation, and ophthalmic artery aneurysms.18,20 LSOC provides a narrower access to the Sylvian fissure and may be most suited to aneurysms of terminal ICA (posterior communicating artery [PComA], anterior choroidal artery), simple ACA, and AComA. Aneurysms of ACA and AComA may be more amenable to SOC.18 Additional factors considered in tailoring the approach are orientation and rupture status of the aneurysm, visualization of the proximal, distal, and perforating vessels, presence of brain swelling and hematoma, and surgeon comfort. The choice of incision location is up to both surgeon and patient.Clinical Outcomes of Mini-Craniotomy SurgeriesAmong the MIM variations, most experience over the past 20 years has been gained with the SOC. Aneurysms were located primarily in the MCA (29.2%–36.43%), AComA (23.0%–46.6%), and ICA and PComA (13.4%–27.7%).8,13,15,24,25 Early series focused on the feasibility of accessing a given aneurysm location through this approach,12–14 whereas subsequent reports compared clinical outcomes of patients with ruptured and unruptured aneurysms treated using the SOC as compared with PTC.8,11,15,24–27Functional outcomes were consistently comparable between SOC and PTC. Fischer et al reported their 20-year experience of 1297 aneurysm operations, in which SOC constituted 74.7%.15 Good outcome (mRS≤2) was reported in 96.6% and 72.2% for unruptured and ruptured aneurysms, respectively. Similarly, Radovanovic et al reported a matched case–control series of 30 consecutive unruptured and 24 ruptured aneurysm cases treated with SOC and PTC. Good outcome (mRS≤2) was achieved in all unruptured cases and 91.7% of SOC for ruptured cases, versus 86.9% of PTC.8 Comparable results were reported in studies of ruptured aneurysms by Chalouhi et al and Paladino et al, in which favorable outcomes (GOS≥4) occurred in 76.6% to 82.6% of SOC and 75% to 79.5% of PTC cases.11,24Intraoperative rupture (IOR), a factor that may adversely impact functional outcome from aneurysm surgery, was analyzed in a systematic review of 9488 aneurysms treated by SOC and PTC over 15 years.26 Overall, IOR rate was 5.8% in SOC versus 10.1% in PTC, but among 3039 ruptured aneurysms, there was a statistically higher IOR rate of 19.4% in SOC versus 13.8% in PTC (odds ratio 1.5, 95% confidence interval 1.003–2.119, P<0.05).26 In contrast, IOR rates for SOC were lower in ruptured aneurysms by Radovanovic et al (12.5%) and Chalouhi et al (10.6%), and no statistical difference was noted when compared with PTC in these more recent series.8,24 Caplan et al reported their experience of 82 unruptured aneurysms treated with the MPTC over 4.5 years, which included MCA (44%), PComA (27%), and paraophthalmic artery (27%).20 Of these, 84.2% of aneurysms were clipped, 13.4% were wrapped with cotton and fibrin glue, and average length of stay was 4.0 days. Welling et al performed a randomized trial evaluating the clinical, functional, and esthetic results between MPTC and PTC for ruptured and unruptured aneurysms.28 Between the 2 groups, similar mRS scores, mortality, IOR rates (14% for MPTC versus 17% PTC) were reported, but greater cosmetic satisfaction results (79% versus 52%, P=0.07) and significantly reduced degree of temporalis atrophy (14.9% versus 24.3%, P<0.01) were noted for MPTC.28Additional potential benefits of MIM may include reduced operative time, length of inpatient stay, and costs.8,29,30 Radovanovic et al noted that the duration of surgery using MIM was approximately half that of PTC for both ruptured and unruptured aneurysms, and for unruptured aneurysms, length of stay was reduced from an average of 4.3 to 2.3 days.8 This translated to significantly lower total treatment costs for unruptured aneurysms because of shorter length of stay. In fact, some patients within the unruptured cohort were treated on an ambulatory outpatient basis.8,31 Similar conclusions about reduced operating time and length of hospitalization were derived by Cha et al from a series of 61 patients in which LSOC was compared with PTC in cohorts having similar demographics and aneurysm locations.29 Thus, overall, MIM aneurysm surgery seems as safe and effective as PTC, but reduces temporalis atrophy, improves cosmesis, and saves on operating time, hospitalization, and costs.A summary of the major papers reporting clinical outcomes is provided in Table 2.Table 2. Clinical Outcomes for Aneurysm Surgery by Mini-Craniotomy ApproachesAuthors and YearNo. of PatientsNo. of Unruptured Aneurysm, %Intra-Operative Rupture Rate %Length of Stay, DaysGood Outcome, %*Peri-Operative ComplicationsSupraorbital craniotomy (SOC) Paladino et al, 19981137NA3%NA100%1 infection van Lindert et al, 199812139NA3%NANANone Czirják et al, 20011310222 (22%)2.0%NA96%1 PE Mitchell et al, 2005144741 (87%)4.3%NA96%2 infarcts, 1 seizure, 3 postop hematomas Reisch et al, 200527229117 (51%)1.7%NANA†6 infarcts† Chen et al, 200925880 (0%)26.1%NA89%10 infections Fischer et al, 201115793319 (40%)7.7%NA97%/72%‡19 residual aneurysms, 9 infections, 9 cerebrospinal fluid leaks, 14 postop hematomas Chalouhi et al, 201324470 (0%)10.6%NA77%1 post-op hematoma, 1 infection, 4 infarcts Radovanovic et al, 201485430 (56%)0%/12.5%‡2.1/18.2‡100%/83%‡2 CSF leak, 1 seizure, 1 anosmia, 1 infectionLateral supraorbital craniotomy (LSOC) Cha et al, 2012296161 (100%)NA7.9NA4 post-op hematoma Mori et al, 2014305353 (100%)NA2.499%1 MCA infarctMini-pterional craniotomy (MPTC) Caplan et al, 2014207272 (100%)NA3.96NA1 MCA infarct, 2 post-op hematoma Welling et al, 201528289 (32%)14NA86%2 post-op hematomaNA indicates not available.*Good outcomes defined as mRS ≤2 or GOS ≥4.†Outcomes and complications specific for aneurysm surgery unavailable. GOS available for entire cohort, including other pathologies.‡Denotes results separated for unruptured cohort and ruptured cohorts, respectively.Endosope-Assisted Aneurysm SurgeryNeuroendoscopy has increased in popularity with improved instrumentation. Its utility as an adjunct to microsurgical operations has been promoted by Perneczky and Fries.32,33 Modern neuroendoscopes provide excellent illumination in the depth of the surgical field, clear depiction of anatomic details, and extended viewing angles with the ability to see around corners, especially with angled lenses.34 Therefore, they may complement the standard operating microscope, which is restricted to illumination and magnification along a line of sight.33From a neuroanatomical perspective, the endoscope is ideal for visualizing aneurysms arising medially from the ICA, where the direct line of sight is obstructed by ICA or optic apparatus.35 Using 0°- and 45°-4 mm and 30°-2.7 mm endoscopes on cadaveric specimens, Peris-Celda et al evaluated the additional endoscopic exposure and available working room at common aneurysm sites.35 Endoscope-assistance was useful for superior hypophyseal, PComA, and anterior choroidal aneurysms and may decrease the need for gyrus rectus resection for AComA aneurysms. Improved visualization was observed in all anterior circulation aneurysms, except MCA with angled endoscopes, whereas the basilar apex benefitted from the smaller 2.7 mm scope to permit larger working space for dissection.The first report of endoscope-assisted aneurysm surgery was by Fischer and Mustafa in 1994 using a flexible endoscope.36 Subsequent clinical series have used a rigid neuro-endoscope with 0°, 30°, 70°, and 110° view angles.33,34,37–40 In endoscope-assisted craniotomies, the majority of the dissection and exposure is performed with the operating microscope, regardless of whether PTC or a mini-craniotomy is used. The endoscope has 3 applications during aneurysm surgery: inspection before clipping, clipping under endoscopic view, and postclipping evaluation.34 Use of the neuroendoscope before clipping permits a greater appreciation of the regional anatomy, particularly of structures obscured from direct microscopic view. This may reduce unnecessary maneuvers to retract and dissect around the aneurysm and may also reduce the duration of temporary clipping. Clipping under endoscopic view requires a holding device to allow bimanual manipulation during clipping and may only be necessary if visualization of the aneurysm is limited with the operating microscope. Post-clipping evaluation ensures that the aneurysm is completely obliterated, and the perforating vessels and surrounding neural structures are intact where the clip may obstruct direct microscopic view.33,34Several case series have evaluated the usefulness of endoscopy assistance for aneurysm surgery in association with PTC.33,37,38,40 Greater anatomic clarification was identified with endoscopy in 81.5% to 94.9% of aneurysms, but interestingly, information obtained exclusively through endoscopy was found in only 16.7% to 19.0% of aneurysms.33,37 Clip repositioning was required in 6.9% to 11.4% of aneurysms because of incomplete neck obliteration, parent artery or perforator occlusion, and compression of surrounding neural structures.33,37,38 Kalavakonda et al reported one IOR when the endoscope was used without temporary occlusion and recommended that close visualization of a ruptured aneurysm should be performed only during temporary occlusion.37Endoscope-assisted aneurysm surgery has been applied to the SOC.34,39 Fischer et al reported 180 aneurysms in which the endoscope was used before clipping (150 cases), during clipping (4 cases), and after aneurysm clipping (130 cases).34 No adverse events related to endoscopy were observed. However, 38 aneurysms (21.1%) required clip rearrangement because of incomplete aneurysm occlusion or neck remnant (15%) and parent or branch vessel occlusion and perforator inclusion (6.1%). The authors commented that without endoscopy, the incomplete clipping and perforator occlusion rates would have been 18.9% and 8.3%, respectively. A larger series of 989 ruptured and unruptured aneurysms treated with endoscope-assisted SOC was also presented by Reisch et al.39 Favorable outcome scores (mRS≤2) for ruptured and unruptured aneurysm cohorts were present in 72.2% and 96.6%, respectively. Suboptimal or incorrect clip position was detected in 19.1% of aneurysms, which were subsequently corrected.There are some disadvantages associated with endoscope-assisted microsurgery. Using both the microscope and endoscope necessitates switching between the 2 modalities. The introduction and withdrawal of the endoscope from the surgical field should be monitored under microscopic vision.33 Decreased awareness of the endoscope may result in inadvertent movements causing contusions on the brain and, at worst, rupture of the aneurysm if the endoscope is displaced within close proximity. Maintaining endoscopic and microscopic vision simultaneously requires incorporating the images through picture-in-picture features on the microscope oculars or endoscope monitors.37 Further limitations of neuroendoscopy include the lack of stereoscopic 3-dimensional vision, which is incomparable to the operating microscope, and the inability to operate bimanually without a fixed endoscope holder.38Intraoperative angiography using indocyanine green (ICG) has gained widespread acceptance to evaluate incomplete clipping and occlusion of surrounding vessels. After injection into a peripheral vein, ICG fluorescence is induced as the dye circulates through the cerebral vessels under near-infrared illumination and images are collected through an optical filter.41 Until recently, ICG angiography (ICG-A) was available only with a microscope integrated with near-infrared camera to capture ICG fluorescence. Therefore, ICG-A was affected by the same line-of-sight problems inherent to the operating microscope. Endoscopic ICG-A has now been developed by Bruneau et al and Nishiyama et al, which combines the benefits of endoscopy and ICG-A.41,42 Preliminary experience comparing microscopic with endoscopic ICG-A was published by Mielke et al on a case series of 26 patients with 30 ruptured and unruptured aneurysms.43 No adverse event relating to the application of ICG or endoscopy was found, but several observations were made: (1) endoscopic detection of intra-arterial fluorescence was 10× longer than microscopic detection, thus giving the opportunity to move the endoscope and view the artery–aneurysm complex from multiple angles; (2) less contrast is required for endoscopic ICG-A. In 11 cases (42.3%), additional information was provided by endoscopic ICG-A, such as confirmation of neck remnants and flow in vessels obscured on microscopic ICG-A. As this technology evolves, endoscopy will become a more useful adjunct to improving the safety of aneurysm surgery.41–43 A listing of the advantages and disadvantages of endoscope-assisted aneurysm surgery is provided in Table 3.Table 3. Advantages and Disadvantages of Endoscope-Assisted and Purely Endoscopic Aneurysm SurgeryAdvantagesDisadvantagesEndoscope-assisted aneurysm surgeryExcellent illumination at depth of surgical fieldLack of stereoscopic 3-dimensional visionClear anatomic details and magnificationInability to operate bimanually without a fixed endoscope holder or an assistant driving endoscopeNo line of sight restrictionsRisk of causing brain contusions during introduction and withdrawal of endoscope in and out from the surgical fieldAbility to see around corners (with angled lenses)Vision obscured from fog or blood; need for repeated cleaning of endoscopePossibly greater maneuverability to adjust angles of visionRequires both microscope and endoscopic equipment; set-up may be cumbersome in operating roomUseful forSwitching between microscope and endoscope images unless picture-in-picture feature available (i) Visualization of aneurysms obstructed by ICA or optic apparatusManagement of aneurysm rupture; blood obscuring endoscope (ii) Confirmation of clip placement, complete aneurysm obliteration, and parent/perforator artery patencyICG angiography in its infancyPurely endoscopic aneurysm surgeryAdvantages as per endoscope-assisted aneurysm surgery, plusDisadvantages as per endoscope-assisted aneurysm surgery, plus: No need for switching between microscope and endoscope Purely endoscopic techniques still in infancy; learning curve required May be used with endonasal or even smaller mini-craniotomy approaches Narrow operating corridors restrict fine motor function at depth of surgical field May avoid frontal lobe retraction, gyrus rectus resection for AComA aneurysms with endonasal approach Lack of specifically designed endoscopic instruments for aneurysm clippingAComA indicates anterior communicating artery; ICA, internal carotid artery; and ICG, indocyanine green.Purely Endoscopic Aneurysm SurgeryPurely endoscopic craniotomy for aneurysm clipping is still in its infancy. Currently, few case reports exist using endoscopic transcranial and endonasal approaches. Perneczky reported 7 aneurysms clipped with exclusive use of the endoscope through a PTC opening.44 More recently, Radovanovic performed a purely endoscopic aneurysm clipping through a 2×2 cm craniotomy with no complications and good cosmetic result.45Endoscopic endonasal clipping of medially projecting paraclinoid aneurysms have been published in sporadic case reports.46,47 Proximal control was obtained at the cavernous ICA through wide sphenoid sinus opening, whereas distal control required extensive transplanum drilling.46 Satisfactory clinical and radiological outcomes were obtained without complications. In cadaveric studies, Lai et al confirmed the feasibility of using an endoscopic endonasal technique with bimanual access to the paraclinoid ICA and AComA complex and the ability to place an aneurysm clip for proximal and distal control.48,49 As an approach, endoscopic endonasal surgery has the benefit of panoramic vision of the surgical field without frontal lobe retraction, gyrus rectus resection for AComA, and avoiding extensive anterior clinoidal drilling and optic nerve manipulation for paraophthalmic aneurysms.48,49However, several important caveats should be noted: (1) long narrow corridors restrict fine motor function at the target and may impair dissection of vessels and manipulation of the aneurysm clip; (2) depth perception is limited by the 2-dimensional view obtained through current endoscopes; (3) specifically designed endoscopic instrumentation for aneurysm surgery are not yet available; (4) management of an IOR may be problematic with significant bleeding obscuring the view of the endoscope; (5) aneurysm recurrence and retreatment will be made even more difficult with the presence of a previous aneurysm clip; (6) endoscopic surgery requires a specific skill set that involves a learning curve and a gradual transition from simple to complex skull base pathologies.40,49 A listing of the advantages and disadvantages of purely endoscopic aneurysm surgery is provided in Table 3.ConclusionsThe use of minimally invasive approaches to treat ruptured and unruptured aneurysms continues
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